* Department of Microbiology, Immunology and Cell Biology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia 265069177; NIOSH-HELD-ASB, 1095 Willowdale Rd., MS L-4218, Morgantown, West Virginia 26505
1 To whom correspondence should be addressed at Department of Microbiology, Immunology and Cell Biology, Health Sciences Center North, P.O. Box 9177, West Virginia University, Morgantown, WV 265069177. Fax: 3042937823. E-mail: rschafer{at}hsc.wvu.edu.
Received March 21, 2005; accepted June 7, 2005
![]() |
ABSTRACT |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
![]() |
INTRODUCTION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Propanil is an amide class herbicide that induces thymic atrophy and splenomegaly. Numerous studies have established that exposure to propanil can inhibit the function of a variety of immune cell populations including macrophages, T cells, and natural killer cells (Barnett and Gandy, 1989; Barnett et al., 1992
; Xie et al., 1997
; Zhao et al., 1998
). Murine studies have demonstrated that propanil inhibits the antibody response in the spleen to the model T cellindependent type 2 (TI-2) antigen DNP-Ficoll and the T-dependent (TD) antigen sheep red blood cells (SRBC) (Barnett and Gandy, 1989
; Barnett et al., 1992
). 2,4-D is a chlorinated phenoxy compound designed as a synthetic form of the plant hormone auxin (Munro et al., 2002
). Reports on the immunotoxic effects of 2,4-D are inconclusive. Studies using a mouse model demonstrated that oral exposure to 2,4-D at the time of vaccination with SRBC increased the number of antibody-producing cells (ASC) in the spleen (Blakley, 1986
). Conversely, another report found that exposure to a mixture of 2,4-D and the herbicide picloram decreased the number of plaque-forming cells in the spleen following SRBC vaccination (Blakley, 1997
). Thus, additional studies are needed to determine the effects of 2,4-D on the humoral immune response.
S. pneumoniae kills approximately 1 million children aged 5 years or younger annually and remains one of the most common causes of pneumococcal death worldwide. Because of its prevalence, it is a well-characterized model for studying the humoral immune response. Vaccination with HKSP elicits a TD antibody response and a TI-2 antibody response (Wu et al., 1999). Pneumococcal surface protein A (PspA) is a TD antigen on S. pneumoniae that acts as a virulence factor by inhibiting the functions of complement (Tu et al., 1999
). Phosphorylcholine (PC) is a cell wall polysaccharide and the immunodominant antigen that elicits the TI-2 antibody response. In addition, PC is a virulence factor that functions by transporting the bacterium across the epithelial and endothelial membranes (Cundell et al., 1995
; Tuomanen et al., 1995
). Current vaccine strategies use a 23-valent polysaccharide vaccine or a 7-valent conjugate vaccine, both of which produce a robust anti-polysaccharide response (Bogaert et al., 2004
). The kinetics of the serum antibody response and the predominant isotypes produced to PspA and PC are well characterized (Wu et al., 1999
, 2000
).
Our laboratory focuses on studying potential synergistic effects on the immune system after exposure to a mixture of propanil and 2,4-D. Previous studies have shown that exposure to either propanil or 2,4-D alone induced thymic atrophy and reduced the number of double positive (CD4+CD8+) thymocytes (de la Rosa et al., 2005). In the bone marrow, exposure to either herbicide alone decreased the number of pre-B (B220+CD43+IgMlow) cells and IgM+ B (B220+CD43-IgMhi) cells (de la Rosa et al., 2003
). However, exposure to the mixture of propanil and 2,4-D caused greater-than-additive decreases in the same cell populations in the thymus and bone marrow, suggesting that interactions of the mixture increased the toxicity of the individual chemicals (de la Rosa et al., 2003
, 2005
).
Based on the previous reports on the immunotoxic effects of propanil and 2,4-D, it was originally hypothesized that exposure to the herbicides would inhibit the humoral immune response after vaccination with HKSP and that exposure to the mixture would be more immunotoxic than the individual compounds. However, in contrast to the hypothesis, the results demonstrated that propanil and 2,4-D differentially affected the immune response to HKSP and there were no apparent interactions between the two herbicides. Exposure to propanil significantly increased the number of PC-specific ASC in the spleen. 2,4-D had no effect on the PC response in the spleen but significantly decreased the number of PC-specific ASC in the bone marrow. The decrease in ASC in the bone marrow after exposure to 2,4-D correlated with a significant decrease in the PC-specific serum antibody titers. There was no effect on the response to PspA by any of the treatments. In addition, these results extend our knowledge of the humoral immune response to vaccination with HKSP by characterizing the primary antibody response to PC in the bone marrow and the spleen in conjunction with the serum antibody response.
![]() |
MATERIALS AND METHODS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Chemicals.
Propanil (3,4-dichloropropionanilide, 99% pure) was purchased from Chem Service (West Chester, PA). Commercial-grade 2,4-D amine (47.2% dimethylamine salt of 2,4-dichlorophenoxyacetic acid, 52.8% inert ingredients, Universal Cooperatives, Inc., Minneapolis, MN) was purchased from Southern States Cooperative (Morgantown, WV).
Bacterial preparation and immunization.
S. pneumoniae strain R36A (a gift from Meenal Elliott, West Virginia University) an avirulent, nonencapsulated strain, was used for all experiments. Strain R36A was chosen because it is a commonly used strain of S. pneumoniae, and the kinetics of the serum antibody response and the predominant isotypes to PC and PspA have been well established (Wu et al., 1999, 2000
). Strain R36A was grown to mid-log phase in Todd-Hewitt broth (Becton Dickinson, Sparks, MD) +.05% yeast extract (Becton Dickinson) and stored at 70°C. For immunization, stock was cultured in a candle jar for 18 h at 37°C on blood agar plates (Becton Dickinson). A few characteristic colonies were selected and suspended in 200 ml Todd-Hewitt broth +.05% yeast extract. Bacteria were grown at 37°C to an absorbance reading at 650 nm of 0.4. Bacteria were heat killed for 4 h at 60°C. A final concentration of 109 CFU/ml was established in PBS based on colony counts. Sterility was confirmed by culture. Heat-killed stock was stored at 20°C in 1-ml aliquots. Mice were immunized intraperitoneally (ip) with 2 x 108 CFU.
Exposure of mice to herbicides.
Mice (56/ group) were treated with either single doses of herbicides (propanil or 2,4-D) or a 1:1 mixture of both herbicides by ip injection within 1 h of HKSP vaccination. Mice were treated with a range of concentrations of herbicide based on milligrams of herbicide/ kilogram of body weight (mg/kg). Propanil was dissolved in peanut oil and animals were treated with 25, 50, 100, or 150 mg/kg. 2,4-D was diluted in sterile PBS and mice were treated with 150 mg/kg. The 2,4-D concentration was based on the amount of active 2,4-D in the commercial preparation. The route of exposure and the doses used were based on previous studies that demonstrated a mixture interaction at 150 mg/kg propanil and 150 mg/kg 2,4-D on thymocyte populations (de la Rosa et al., 2005). Control animals were treated with the vehicle peanut oil only, as previous studies had determined that there was no difference between animals treated with the peanut oil vehicle compared to the PBS vehicle.
Preparation of spleen and bone marrow cell suspensions.
Mice were euthanized with 100 µl Nembutal sodium solution (50 mg/ml, Abbott Laboratories, North Chicago, IL) on days 3, 5, 7, 10, and 14 after herbicide exposure and vaccination. Spleen wet weights were recorded. Spleens were mechanically dissociated through Spectra nylon mesh (Spectrum Labs, Rancho Dominguez, CA) in complete cell medium containing RPMI-1640 (BioWhitaker, Walkersville, MD), 10% heat inactivated fetal bovine serum (FBS, Hyclone Laboratories, Inc, Logan, UT), 10 mM HEPES (Sigma, St. Louis, MO), 1 mM L-glutamine (Gibco, Rockville, MD), 5 x 105 M 2-mercaptoethanol (Sigma), 100 U/ml penicillin (Gibco), and 100 µg/ml streptomycin (Gibco). To collect bone marrow cells, one hind leg was removed from each animal. Femur and tibia were flushed with complete media for single cell suspensions. Red blood cells in the spleen and bone marrow populations were lysed with Tris-buffered ammonium chloride. Cell suspensions were washed twice and counted by hemacytometer in Trypan blue.
Flow cytometric analysis.
Cells were stained with the appropriate combinations of rat anti-mouse B220-APC (RA3-6B2), rat anti-mouse CD23-PE (B3B4), rat anti-mouse CD21-FITC (7G6), rat anti-mouse CD4-FITC (GK1.5), or rat anti-mouse CD8-PE (536.7) (all from BD PharMingen, San Diego, CA). All steps were performed in PBS supplemented with 1% FBS and 0.04% sodium azide (Sigma). Briefly, 1 x 106 cells were stained in a total volume of 25 µl of antibodies at the appropriate concentrations for 25 min on ice in the dark. After incubation, cells were washed twice and fixed in 0.04% paraformaldehyde overnight at 4°C (Fisher Scientific, Pittsburgh, PA). The following day cells were washed twice to remove the paraformaldehyde and resuspended in 1 ml of staining medium. For each sample, 10,000 cells were collected for analysis on a Becton-Dickinson FACScan (Becton Dickinson Immunocytometry Systems, Mansfield, MA). Analysis was performed using WinMDI software (Joseph Trotter, Scripps Institution, San Diego, CA). Population percentages, obtained from flow cytometric analysis, were used to calculate the absolute cell number by multiplying the percentage of cells in a population by the total number of cells harvested per organ. Marginal zone B cells are defined as B220+CD21/35hi CD23neg/low, follicular B cells are defined as B220+CD21/35int CD23hi (Oliver et al., 1997
). B cells are defined as all cells that are B220+ and include marginal zone B cells and follicular B cells.
Measurement of antibody secreting B cells (ASC) in the bone marrow and spleen.
Acrowell 96-well filter plates (Pall Life Sciences, Ann Arbor, MI) were coated with 50 µl PC-BSA (Biosearch Technologies, Novato, CA) (10 µg/ml) or 50 µl PspA (10 µg/ml) (PspA was a generous gift from Clifford Snapper, Uniformed Services University of the Health Sciences) overnight at 4°C. In all subsequent steps, plates were washed with PBS +.01% Tween-20. Plates were blocked with 200 µl/well complete medium + 25% FBS for 2 h at 37°C. Plates were washed, and cells (100 µl/well) were then added at a concentration of 5 x 106 cells/ml or 1 x 106 cells/ml. All samples were plated in triplicate. Plates were incubated for 46 h at 37°C in a 5% CO2 incubator. Plates were washed and goat anti-mouse alkaline phosphatase (AP) conjugated IgG, IgG1, IgG2a, IgG2b, IgG3, or IgM antibodies (Southern Biotechnology Associates, Birmingham, AL), diluted 1/2000 in PBS + 1% BSA +.05% Tween-20, were added to the appropriate wells (100 µl/well). Plates were incubated overnight at 4°C and washed. SIGMAFAST 5-bromo-4-chloro-3-indolyl phosphate/nitro blue tetrazolium tablets (Sigma-Aldrich, St. Louis, MO) were dissolved in distilled water and added at 100 µl/ well. Color development was stopped by washing with distilled water. The number of spots/well was counted using a dissection microscope (Olympus Optical Co., Melville, NY). The number of ASC was calculated by using the mean number of spots from triplicate wells. Data are expressed as the number of ASC per 1 x 106 B cells or as the number of ASC per spleen or bone marrow.
Measurement of PC- and PspA- specific titers.
Serum samples were prepared via blood collected from the heart. Immulon 2 plates (for PC) or Immulon 4 plates (for PspA) (ThermoLabsystems, Franklin, MA) were coated overnight at 4°C with 5 µg/ml PC-BSA or 10 µg/ml PspA (50 µl/well). Plates were washed and then blocked with 3% BSA + PBS at 37°C for 2 h. Plates were washed and 100 µl/well of twofold dilutions of sera in PBS +1% BSA were added starting at 1/400 for the IgG and IgM ELISAs and 1/250 for the IgG subclasses. Plates were then incubated for 1 h at 37°C and washed. AP conjugated antibodies (100 µl/well) were added for 1 h at 37°C. Plates were washed and phosphatase substrate tablets (Sigma-Aldrich) were dissolved in PNPP (p-nitrophenyl phosphate, disodium salt) substrate buffer. Plates were developed and absorbance was read at 405 nm on a µQuant spectrophotometer (Bio-Tek instruments, Winooski, VT) using KCJunior software (Bio-Tek instruments). To determine the titer, a standard pooled serum sample was diluted and plated on each ELISA plate. The titer for each sample was determined by comparison to the standard sera when the OD 405 nm for the standard was 0.200 at a 1:3200 dilution for IgM and IgG or at 1:2000 for IgG2b and IgG3. These dilutions were chosen because they are in the linear part of the curve for the respective isotypes.
Measurement of ex vivo PC-specific antibody production.
Spleen cells were cultured in vitro with no additional stimulation for 5 days at 37°C and 5% CO2 at a concentration of 5 x 105 cells/ml in 500 µl complete medium in 48-well tissue culture plates (Costar, Corning Inc., Acton, MA). All cultures were performed in duplicate. The protein synthesis inhibitor cycloheximide was added to replicate samples at a concentration of 75 µg/ml (50 µl/well) to distinguish the amount of antibody produced de novo in culture from preformed antibody secreted during the culture period (Dhanjal et al., 1992). Supernatants were collected and antibody ELISAs were performed as described above. De novo antibody synthesis was determined by subtracting the absorbance readings from cycloheximide-treated cells from absorbance readings from non-cycloheximidetreated cells.
Statistics.
One-way analysis of variance (ANOVA) was performed for all statistical analyses using a Dunnett's t-test to compare herbicide-treated animals with control animals. A significance level of p 0.05 was used for all tests. Identification of possible mixture interactions was determined by means ofa partial factorial design. A mixture interaction was defined as the sum of the responses of the individual components of the mixture being significantly different from the response of the mixture treatment. Statistical analysis was performed using JMP software (SAS Institute Inc., Cary, NC). All experiments were performed three or more times with similar results. The figures are representative data from one experiment.
![]() |
RESULTS |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Initial experiments in vehicle control animals immunized with HKSP demonstrated that IgM ASC were detectable at day 3 (30 ± 10 ASC/1 x 106 B cells, Fig. 1A) and peak 5 to 7 days post-exposure (144 ± 73 ASC and 252 ± 42 ASC, respectively, Fig. 1A). There was no statistical difference between day 5 and day 7. By day 10, the number of splenic ASC in control animals had decreased twofold (83 ± 35 ASC). The predominant isotypes produced were IgM, IgG2b, and IgG3, and all had similar kinetics (Fig. 1A, 1B, and 1C, respectively). Comparable results were obtained when the number of ASC per spleen were determined (Fig. 1D, 1E, and 1F). IgG1 and IgG2a were below the limit of detection by ELISPOT at all time points.
|
Previous studies had demonstrated that propanil treatment induces splenomegaly (Barnett and Gandy, 1989). The spleen weights were determined after herbicide exposure and HKSP vaccination. Propanil and the mixture of propanil and 2,4-D, but not 2,4-D alone, caused an increase in spleen weight at 7 and 10 days post-exposure (Fig. 2). However, flow cytometric analysis of the major cell populations in the spleen at all time points determined that there were no significant changes in any of the treatment groups in the number of total B220+ B cells, CD21/35hi CD23neg/low marginal zone B cells, CD21/35int CD23hi follicular B cells, CD4+ T cells, and CD8+ T cells (Table 1, representative data from day 7 post-exposure and vaccination). The total number of bone marrow cells was also comparable for the vehicle (28.5 ± 1.8 x 106), propanil (27.6 ± 3.5 x 106), 2,4-D (25.4 ± 3.8 x 106), and mixture-treated groups (27.4 ± 3.2 x 106).
|
|
|
|
|
|
|
![]() |
DISCUSSION |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Propanil magnified the splenic PC-specific ASC response without altering the kinetics of the response or shifting the isotype composition. The earliest observed increase due to propanil exposure was 5 days post-exposure. Maximal effects were observed at day 7, and ASC decreased by day 10. Both T helper 1 (Th1) and Th2 cytokines alter the antibody response. IFN-, a Th1 cytokine, promotes IgG3 production and TGF-ß, a Th2 cytokine, promotes a shift to IgG2b production (Stavnezer, 1996
). The retention of the predominant PC-specific isotypes IgG3 and IgG2b suggests that propanil does not skew the cytokine profile of the immune response. The kinetics of the splenic antibody response in propanil and vehicle-treated animals were similar, suggesting that proliferation and activation is not unregulated as would be indicated by a continued increase in ASC at day 10.
Despite a severalfold increase in the number of PC-specific ASC in the spleen, and an increased ex vivo production of PC-specific antibody by splenocytes from propanil-treated animals in comparison to the control, the serum antibody titers were comparable for the two groups. There are several possible explanations for this result. First, it is possible that the increased amount of antibody produced in propanil-treated animals remains localized to the spleen. Second, the antibodies produced in the spleen in propanil-treated mice may be rapidly catabolized if serum antibody levels are at a saturated concentration; therefore no increase in serum titers would be detected. However, the second possibility is unlikely because mixture-treated animals also had increased splenic ASC but reduced serum titers. Several earlier reports established the bone marrow as the primary source of serum antibodies (reviewed in Benner et al., 1981). Exposure to propanil had no effect on the number of bone marrow PC-specific ASC. In contrast to propanil, 2,4-D decreased PC-specific ASC in the bone marrow and the decrease correlated with a decrease in PC-specific titers. Splenic ASC were comparable to control animals after 2,4-D exposure. Taken together, the results suggest that 2,4-D decreased serum PC-specific titers by decreasing bone marrow ASC, and they demonstrate the importance of bone marrow ASC for PC-specific titers during the primary response to HKSP. The ability of a chemical to decrease the number of plasma cells in the bone marrow could have long-term implications for maintaining circulating levels of protective antibody after immunizations.
In contrast to the results presented here, propanil exposure has previously been reported to suppress the number of plaque-forming cells after immunization with the TI-2 antigen DNP-Ficoll, and the TD antigen SRBC (Barnett and Gandy, 1989; Barnett et al., 1992
). The nature of the antigen may be important for the immunomodulation of the immune response by propanil. DNP-Ficoll and PC are both model TI-2 antigens. However, in the present study, PC is presented in the context of whole HKSP, a complex particulate immunogen. It was previously demonstrated that the requirements for the humoral response to PC, after immunization with HKSP, is substantially different than after immunization with purified polysaccharide preparations (Wu et al., 1999
). Although the PC antibody response is classically considered to be T-independent, Wu et al. (1999)
demonstrated that the IgG isotype responses to PC after immunization with HKSP was decreased in T cell receptor ß knockout mice. In addition, they demonstrated that CD4+ T cells and CD8+ T cells contributed to an optimal antibody response, and the PC response was significantly decreased in CD40L knockout mice (Wu et al., 1999
). Further studies demonstrated that noncognate T cell help was required for an optimal PC response after HKSP immunization (Wu et al., 2002
). Therefore, propanil could affect one of the components necessary for the response to PC after immunization with HKSP that is not required after immunization with soluble DNP-Ficoll.
The time of exposure to the herbicide may also be important to the subsequent effects on the immune response. In the previous studies that demonstrated propanil suppressed the plaque-forming cell response to SRBC and DNP-Ficoll, the antigens were administered 3 days after propanil exposure (Barnett and Gandy, 1989; Barnett et al., 1992
). In the present study, propanil was administered at the time of HKSP vaccination. This may suggest that propanil is acting as an adjuvant to affect innate immune mechanisms and enhance the immune response to PC.
The antibody response to vaccination with HKSP is influenced by the early innate immune response. S. pneumoniae has pathogen-associated molecular patterns on its surface that can stimulate signaling pathways through pattern recognition receptors such as toll-like receptor-2 (TLR2) (Yoshimura et al., 1999). It was recently demonstrated that the IgG2b and IgG3 antibody response to PC after immunization with heat-killed S. pneumoniae type 14 is decreased in TLR-2 knockout mice (Khan et al., 2005
). The complement pathways are also important for the innate immune response to S. pneumoniae that can influence the subsequent adaptive immune response (Brown et al., 2002
). Conjugation of the complement component C3d to pneumococcal capsular polysaccharide, has been demonstrated to enhance the antibody response to the polysaccharide dependent on the dose of antigen (Test et al., 2001
). Similarly, preliminary studies in our laboratory suggest that the dose of HKSP is important, as mice vaccinated with suboptimal doses of HKSP did not have an increase in ASC. The effect of propanil on specific components of the innate immune response has not been investigated.
Propanil may alter the immune response through interactions with the endocrine system. Propanil induces thymic atrophy primarily through the induction of glucocorticoids; however, inhibition of glucocorticoid production does not completely abrogate thymic atrophy (Cuff et al., 1996; de la Rosa et al., 2005
). In addition, glucocorticoids are reported to inhibit Th1 responses and enhance Th2 responses (Ashwell et al., 2000
; Miyaura and Iwata, 2002
). Propanil did not alter the major isotype response to PC, which suggests that the T-cell response and subsequent production of cytokines driving B-cell switching were not affected. This further suggests that additional mediators may play a role in the immunotoxic effects of propanil. Propanil also decreases the preB-cell and IgM+ B-cell populations in the bone marrow via an unknown mechanism (de la Rosa et al., 2003
). Similar to exposure to propanil, 17ß-estradiol exposure has been shown to induce thymic atrophy and decrease immature B-cell populations in the bone marrow (Erlandsson et al., 2003
). Chronic exposure to 17ß-estradiol has been reported to increase ASC to bacterial and autoantigens in C57BL/6 mice (Verthelyi and Ahmed, 1998
). In addition, exposure to 17ß-estradiol was demonstrated to increase activation of the marginal zone B-cell population and lead to the production of autoantibodies by the marginal zone B cells (Grimaldi et al., 2001
). Marginal zone B cells are crucial in the generation of the immune response to TI-2 antigens (reviewed in Zandvoort and Timens, 2002
). Mice deficient in marginal zone B cells have a deficient antibody response to TI-2 antigens (Guinamard et al., 2000
). If propanil induced the production of 17-ß estradiol it could enhance the antibody response to PC through the effects of 17-ß estradiol on the marginal zone B-cell population. Preliminary studies in our laboratory have demonstrated that propanil does not increase the number of PC-specific splenic ASC in ovariectomized mice, suggesting an important potential role for 17ß-estradiol.
The mechanism by which 2,4-D decreased the bone marrow PC-specific ASC is unknown. However, there are several possibilities. Homing of plasma cells from the spleen to the bone marrow is dependent on the expression of the chemokine receptor CXCR4 on splenic plasma cells and its ligand, CXCL12, in the bone marrow (Erickson et al., 2003). The splenic ASC in 2,4-Dtreated mice could be defective in the expression of CXCR4. It is also possible that production of CXCL12 in the bone marrow could be defective. Finally, support of plasma cells in the bone marrow could be affected as a result of damage to the bone marrow microenvironment.
In contrast to the effect on the TI-2 antigen PC, exposure to propanil, 2,4-D or the mixture had no effect on the response to the TD antigen PspA. The number of PspA-specific ASC in the spleen and the serum titers to PspA were comparable to the controls for all of the treatment groups. This could suggest that the effects of both propanil and 2,4-D occur early after vaccination when the TI-2 antigen response is being generated. If propanil has effects on the innate immune system or on marginal zone B cells, which are critical to the response to TI-2 antigens, as discussed above, the effects may not affect the subsequent response to the TD antigen PspA. A second possibility is that the time of exposure to the herbicides during the immune response to each antigen is critical. In the experiments presented here, herbicide exposure occurred on the day of HKSP vaccination. The peak response to PC was determined 7 days post-exposure, whereas the peak response to PspA is at day 14. If the herbicides mediate their effect during the time antigen-specific B cells are undergoing activation or expansion, and the effect is short-term, then the later response to PspA may not be affected. Similar to PspA, propanil exposure does not increase the number of splenic IgM ASC to SRBC, another TD antigen, when administered at the time of SRBC immunization (de la Rosa, unpublished results).
As the use of herbicides escalates, it is necessary to have an accurate understanding of the risks associated with their use. This report illustrates the importance of studying immunotoxic effects using naturally occurring microbial pathogens and the diverse effects that different compounds can have. The enhanced antibody response after exposure to propanil has implications for the potential of this class of compounds to be environmental factors in autoimmune disease. In contrast, other compounds, such as 2,4-D, may impair the ability of the host to mount an appropriate protective immune response after vaccination.
![]() |
ACKNOWLEDGMENTS |
---|
![]() |
REFERENCES |
---|
![]() ![]() ![]() ![]() ![]() ![]() ![]() |
---|
Barnett, J. B., and Gandy, J. (1989). Effect of acute propanil exposure on the immune response of C57Bl/6 mice. Fundam. Appl. Toxicol. 12, 757764.[CrossRef][ISI][Medline]
Barnett, J. B., Gandy, J., Wilbourn, D., and Theus, S. A. (1992). Comparison of the immunotoxicity of propanil and its metabolite, 3,4-dichloroaniline, in C57Bl/6 mice. Fundam. Appl. Toxicol. 18, 628631.[CrossRef][ISI][Medline]
Benner, R., Hijmans, W., and Haaijman, J. J. (1981). The bone marrow: the major source of serum immunoglobulins, but still a neglected site of antibody formation. Clin. Exp. Immunol. 46, 18.[ISI][Medline]
Blakley, B. R. (1986). The effect of oral exposure to the n-butylester of 2,4-dichlorophenoxyacetic acid on the immune response in mice. Int. J. Immunopharmacol. 8, 9399.[CrossRef][ISI][Medline]
Blakley, B. R. (1997). Effect of roundup and tordon 202C herbicides on antibody production in mice. Vet. Hum. Toxicol. 39, 204206.[ISI][Medline]
Bogaert, D., Hermans, P. W., Adrian, P. V., Rumke, H. C., and De Groot, R. (2004). Pneumococcal vaccines: An update on current strategies. Vaccine 22, 22092220.[CrossRef][ISI][Medline]
Brown, J. S., Hussell, T., Gilliland, S. M., Holden, D. W., Paton, J. C., Ehrenstein, M. R., Walport, M. J., and Botto, M. (2002). The classical pathway is the dominant complement pathway required for innate immunity to Streptococcus pneumoniae infection in mice. Proc. Natl. Acad. Sci. U.S.A. 99, 1696916974.
Cuff, C. F., Zhao, W., Nukui, T., Schafer, R., and Barnett, J. B. (1996). 3,4-Dichloropropionanilide-induced atrophy of the thymus: Mechanisms of toxicity and recovery. Fundam. Appl. Toxicol. 33, 8390.[CrossRef][ISI][Medline]
Cundell, D. R., Gerard, N. P., Gerard, C., Idanpaan-Heikkila, I., and Tuomanen, E. I. (1995). Streptococcus pneumoniae anchor to activated human cells by the receptor for platelet-activating factor. Nature 377, 435438.[CrossRef][ISI][Medline]
de la Rosa, P., Barnett, J., and Schafer, R. (2003). Loss of pre-B and IgM(+) B cells in the bone marrow after exposure to a mixture of herbicides. J. Toxicol. Environ. Health A 66, 22992313.[ISI][Medline]
de la Rosa, P., Barnett, J. B., and Schafer, R. (2005). Characterization of thymic atrophy and the mechanism of thymocyte depletion after in vivo exposure to a mixture of herbicides. J. Toxicol. Environ. Health A 68, 8198.[Medline]
Dhanjal, M. K., Towler, A. E., Tuft, S., Hetzel, C., Richards, D., and Kemeny, D. M. (1992). The detection of IgE-secreting cells in the peripheral blood of patients with atopic dermatitis. J. Allergy Clin. Immunol. 89, 895904.[ISI][Medline]
Erickson, L. D., Lin, L. L., Duan, B., Morel, L., and Noelle, R. J. (2003). A genetic lesion that arrests plasma cell homing to the bone marrow. Proc. Natl. Acad. Sci. U.S.A. 100, 1290512910.
Erlandsson, M. C., Jonsson, C. A., Islander, U., Ohlsson, C., and Carlsten, H. (2003). Oestrogen receptor specificity in oestradiol-mediated effects on B lymphopoiesis and immunoglobulin production in male mice. Immunology 108, 346351.[CrossRef][ISI][Medline]
Farenhorst, A., and Prokopowich, B. (2003). The effect of propanil co-application on 2,4-D sorption by soil. J. Environ. Sci. Health B 38, 713721.[ISI][Medline]
Faustini, A., Settimi, L., Pacifici, R., Fano, V., Zuccaro, P., and Forastiere, F. (1996). Immunological changes among farmers exposed to phenoxy herbicides: Preliminary observations. Occup. Environ. Med. 53, 583585.[Abstract]
Grimaldi, C. M., Michael, D. J., and Diamond, B. (2001). Cutting edge: Expansion and activation of a population of autoreactive marginal zone B cells in a model of estrogen-induced lupus. J. Immunol. 167, 18861890.
Guinamard, R., Okigaki, M., Schlessinger, J., and Ravetch, J. V. (2000). Absence of marginal zone B cells in Pyk-2-deficient mice defines their role in the humoral response. Nat Immunol. 1, 3136.[CrossRef][ISI][Medline]
Khan, A. Q., Chen, Q., Wu, Z. Q., Paton, J. C., and Snapper, C. M. (2005). Both innate immunity and type 1 humoral immunity to Streptococcus pneumoniae are mediated by MyD88 but differ in their relative levels of dependence on toll-like receptor 2. Infect. Immun. 73, 298307.
Meister, R. T., and Sine, C. (Eds.). (2003). Crop Protection Handbook (vol 86). Meister Publishing Company, Willoughby, OH.
Miyaura, H., and Iwata, M. (2002). Direct and indirect inhibition of Th1 development by progesterone and glucocorticoids. J. Immunol. 168, 10871094.
Munro, I. C., Carlo, G. L., Orr, J. C., Sund, K. G., Wilson, R. M., Kennepohl, E., Lynch, B. S., Jablinske, M., and Lee, N. L. (2002). A comprehensive, integrated review and evaluation of the scientific evidence relating to the safety of the herbicide 2,4-D. J. Am. Coll. Toxicol. 11, 559663.
Oliver, A. M., Martin, F., Gartland, G. L., Carter, R. H., and Kearney, J. F. (1997). Marginal zone B cells exhibit unique activation, proliferative and immunoglobulin secretory responses. Eur. J. Immunol. 27, 23662374.[ISI][Medline]
Short, P., and Colborn, T. (1999). Pesticide use in the U.S. and policy implications: A focus on herbicides. Toxicol. Ind. Health 15, 240275.[CrossRef][ISI][Medline]
Stavnezer, J. (1996). Immunoglobulin class switching. Curr. Opin. Immunol. 8, 199205.[CrossRef][ISI][Medline]
Test, S. T., Mitsuyoshi, J., Connolly, C. C., and Lucas, A. H. (2001). Increased immunogenicity and induction of class switching by conjugation of complement C3d to pneumococcal serotype 14 capsular polysaccharide. Infect. Immun. 69, 30313040.
Tu, A. H., Fulgham, R. L., McCrory, M. A., Briles, D. E., and Szalai, A. (1999). Pneumococcal surface protein A inhibits complement activation by Streptococcus pneumoniae. J. Infect. Immun. 67, 47204.
Tuomanen, E. I., Austrian, R., and Masure, H. R. (1995). Pathogenesis of pneumococcal infection. N. Engl. J. Med. 332, 12801284.
Verheul, A. F., Versteeg, A. A., Westerdaal, N. A., Van Dam, G. J., Jansze, M., and Snippe, H. (1990). Measurement of the humoral immune response against Streptococcus pneumoniae type 14derived antigens by an ELISA and ELISPOT assay based on biotin-avidin technology. J. Immunol. Methods 126, 7987.[CrossRef][ISI][Medline]
Verthelyi, D. I., and Ahmed, S. A. (1998). Estrogen increases the number of plasma cells and enhances their autoantibody production in nonautoimmune C57BL/6 mice. Cell Immunol. 189, 125134.[CrossRef][ISI][Medline]
Wu, Z. Q., Khan, A. Q., Shen, Y., Schartman, J., Peach, R., Lees, A., Mond, J. J., Gause, W. C., and Snapper, C. M. (2000). B7 requirements for primary and secondary protein- and polysaccharide-specific Ig isotype responses to Streptococcus pneumoniae. J. Immunol. 165, 68406848.
Wu, Z. Q., Shen, Y., Khan, A. Q., Chu, C. L., Riese, R., Chapman, H. A., Kanagawa, O., and Snapper, C. M. (2002). The mechanism underlying T cell help for induction of an antigen-specific in vivo humoral immune response to intact Streptococcus pneumoniae is dependent on the type of antigen. J. Immunol. 168, 55515557.
Wu, Z. Q., Vos, Q., Shen, Y., Lees, A., Wilson, S. R., Briles, D. E., Gause, W. C., Mond, J. J., and Snapper, C. M. (1999). In vivo polysaccharide-specific IgG isotype responses to intact Streptococcus pneumoniae are T cell dependent and require CD40- and B7-ligand interactions. J. Immunol. 163, 659667.
Xie, Y. C., Schafer, R., and Barnett, J. B. (1997). The immunomodulatory effects of the herbicide propanil on murine macrophage interleukin-6 and tumor necrosis factor-alpha production. Toxicol. Appl. Pharmacol. 145, 184191.[CrossRef][ISI][Medline]
Yoshimura, A., Lien, E., Ingalls, R. R., Tuomanen, E., Dziarski, R., and Golenbock, D. (1999). Cutting edge: recognition of Gram-positive bacterial cell wall components by the innate immune system occurs via Toll-like receptor 2. J. Immunol. 163, 15.
Zandvoort, A., and Timens, W. (2002). The dual function of the splenic marginal zone: essential for initiation of anti-TI-2 responses but also vital in the general first-line defense against blood-borne antigens. Clin. Exp. Immunol. 130, 411.[CrossRef][ISI][Medline]
Zhao, W., Schafer, R., and Barnett, J. B. (1998). Cytokine production by C57BL/6 mouse spleen cells is selectively reduced by exposure to propanil. J. Toxicol. Environ. Health A 55, 107120.[CrossRef][ISI][Medline]
|