Development of dermatitis in CD18-deficient PL/J mice is not dependent on bacterial flora, and requires both CD4+ and CD8+ T lymphocytes

Shayne C. Barlow1, Hui Xu2, Casey T. Weaver3, J. Russell Lindsey1, Trenton R. Schoeb1 and Daniel C. Bullard1

Departments of 1 Genetics, 2 Dermatology and 3 Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA

Correspondence to: D. Bullard; E-mail: pike{at}uab.edu
Transmitting editor: T. Tedder


    Abstract
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
CD18-deficient PL/J mice develop dermatitis characterized by hyperkeratosis, and a mixed dermal and epidermal inflammatory infiltrate. The development of this disease requires low-level CD18 expression and at least two PL/J loci. Currently, the mechanisms by which decreased ß2 integrin expression on leukocytes promotes skin inflammation in PL/J mice are unknown. In these studies, we investigated the role of microbial infection and T lymphocytes in the pathogenesis of this disease. We found that germ-free CD18–/– PL/J mice developed dermatitis indistinguishable from that of mice raised in pathogen-free conditions. Adoptive transfer of CD18–/– PL/J splenocytes into skin disease-resistant CD18+/– PL/J mice failed to induce skin inflammation. However, transfer of CD18+/– splenocytes blocked the progression and ultimately led to resolution of skin disease in the majority of CD18–/– recipients. Depletion of both CD4+ and CD8+ T cells mice prior to onset of the disease significantly delayed the appearance of inflammatory skin disease. In contrast, single depletions of these T cells did not inhibit disease development. These studies show that dermatitis in CD18-deficient PL/J mice is not the consequence of infection, does not require bacterial superantigens, and is mediated by both CD4+ and CD8+ T lymphocytes. Furthermore, they suggest that one possible mechanism for skin disease development in these mice may involve the absence or dysfunctional activity of a regulatory T cell population. These mice may therefore be useful in identifying potential mechanisms of pathogenesis and genetic predisposition in human inflammatory skin diseases.

Keywords: adhesion molecule, CD18, germ-free, psoriasis, T lymphocyte


    Introduction
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The ß2 integrins are expressed exclusively on leukocytes, and participate in many immune and inflammatory processes. These molecules are heterodimeric transmembrane proteins composed of one of four {alpha} subunits (CD11a–d) and a common ß subunit (CD18 or Itgb2) (1). In humans and cattle, spontaneous mutations of the CD18 gene result in the disease leukocyte adhesion deficiency 1, which is characterized by increased circulating leukocyte counts, recurrent infections and impaired wound healing (2,3). Two different lines of gene-targeted mice have now been developed to further study the role of the ß2 integrins in leukocyte-mediated processes. One of these lines, Itgb2tm1bay, is a hypomorphic CD18 mutation that results in low-level expression of the ß2 integrins (4). Mice homozygous for this mutation on a 129/Sv or C57BL/6 strain background appear phenotypically normal, although they do have leukocytosis and show a moderate impairment in neutrophil adhesion in several inflammatory models (5).

We previously reported a contrasting phenotype in CD18 (Itgb2tm1bay) mutant PL/J mice (6). Mice homozygous for this mutation, unlike heterozygotes, spontaneously develop dermatitis with several similarities to human inflammatory skin diseases such as psoriasis (6). The disease is completely penetrant in highly backcrossed mice, and is characterized by erythema, scale and crust formation, and alopecia. Histologically, there is epidermal proliferation, hyperkeratosis, parakeratosis, neutrophil accumulations, and a mixed dermal and epidermal infiltrate including CD4+ and CD8+ lymphocytes. Genetic analyses suggested that at least two other PL/J loci control skin disease susceptibility and severity. Low-level CD18 expression was also required for the development of any skin inflammation, since CD18NULL (Itgb2tm2bay) PL/J mice did not show any evidence of this skin disease (7). At this time, the pathogenetic mechanisms that mediate the initiation and progression of skin inflammation in this model are not known.

The ß2 integrins play central roles in host defense, leukocyte adhesion to endothelium and lymphocyte co-stimulation, and are thus thought to be important in the development of a number of inflammatory skin diseases, including psoriasis, atopic dermatitis and alopecia areata (810). These diseases are thought to result primarily from a dysregulated T cell response in skin (1119). In addition, some forms of psoriasis, such as guttate psoriasis, have also been associated with bacterial infections (20,21). In these patients, it is thought that organisms such as Streptococcus spp. may result in a superantigen response generating activated T cells that cross-react with self-antigens (22). It is possible that altered expression of one or more of the ß2 integrins in the presence of specific genetic modifiers may result in similar immunologic alterations and lead to the development of skin disease in PL/J mice. In these studies we sought to determine whether bacterial infection and/or T cells are involved in the pathogenesis of dermatitis in CD18-deficient PL/J mice. Our findings indicate that skin disease expression is not related to infection, but is mediated by both CD4+ and CD8+ T lymphocytes. In addition, they suggest that low-level expression of the ß2 integrins in PL/J mice may alter the development or function of a regulatory T cell population, which is capable of suppressing skin inflammation.


    Methods
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
Germ-free experiments
Breeding pairs of germ-free Black Swiss mice were purchased from Taconic Farms (Germantown, NY), shipped in germ-free shipping cartons and transferred into flexible film isolators that had been previously sterilized with Exspor (Alcide, Redmond, WA). All isolators were stocked with autoclaved cages, food (LM-485 Autoclavable Rodent Diet; Teklad, Madison, WI), tap water, hardwood chip bedding and other supplies. CD18 mutant (Itgb2tm1bay)+/– PL/J N6 mice were mated and pregnancies were timed by observing for vaginal plugs. At term, the gravid females were euthanized by cervical dislocation and aseptically prepped for abdominal surgery. A ventral midline incision was performed, the uterus was clamped at the level of the cervix and removed, and the entire uterus including pups was transferred into the flexible film isolator through a germicidal trap. Once inside the isolator, the pups were fostered onto recently postpartum Black Swiss mothers. Pups were identified by coat color.

Microbial monitoring of germ-free mice
For the first 2 weeks following the establishment of each isolator, a pooled sample of feces, soiled bedding, sipper tube drinking water and a swab of the isolator’s interior was collected every other day, removed from the isolator, vortexed and cultured. Each sample was inoculated into brain heart infusion broth (37°C, with and without 5% CO2) and thioglycollate medium (37°C, anaerobic) for bacteria, and Sabouraud dextrose broth (25 and 37°C, aerobic). When the animals reached the appropriate age, two animals per isolator were sacrificed for: (i) similar cultures of skin, stomach and large intestine for bacteria and fungi; (ii) serologic testing for cilia-associated respiratory bacillus, mouse cytomegalovirus, Clostridium piliforme, Encephalitozoon cuniculi, lymphocytic choriomeningitis virus, mouse adenovirus, mouse hepatitis virus, mouse rotavirus, mouse thymic virus, minute virus of mice, mouse parvovirus, mouse pox, Mycoplasma pulmonis and pneumonia virus of mice; (iii) testing for ecto- and endoparasites; and (iv) histopathologic examination of all major organs, with generous use of Gram and silver impregnation stains to detect microbial colonization of skin, gastrointestinal and other habitats. Once the isolators were proven germ-free by these tests, they were subsequently monitored weekly by: (i) collection of pooled samples of feces, soiled bedding, sipper tube drinking water and a swab of the isolator’s interior; (ii) culture of the sample on brain heart infusion broth, thioglycollate medium and Sabouraud dextrose broth; and (iii) examination of smears made from the pooled sample, and stained with crystal violet and/or Gram stain. Additionally, at least every other month one or more animals was sacrificed, and evaluated by bacterial and fungal cultures and histopathologic examinations.

Adoptive transfer experiments
CD18+/– or –/– PL/J N6 mice were used for all adoptive transfer studies. Donor animals were anesthetized with 3% methoxyflurane in a bell jar apparatus. The abdomen was aseptically prepped, a ventral midline incision was performed and the spleen was removed. The spleens of the necessary number of animals were pooled, aseptically forced through a 45-µm filter and washed twice with ice-cold HBSS. The pellet was resuspended in an appropriate volume of HBSS, depending on yield, and lymphocytes were isolated using Ficoll-Paque (Amersham Pharmacia, Uppsala, Sweden) according to manufacturer’s directions. For most experiments, 5–15 x 106 isolated cells were washed twice and resuspended in PBS, and injected i.v. into the recipient mice via the lateral tail vein. Some recipient animals were irradiated using a GammaCell 40 (137Ce) irradiation source. Non-lethally irradiated animals were treated with 600 rad, a dose determined to be non-lethal based on previous tests of this mouse strain (unpublished data). Mice were evaluated 1–2 times/week for 4–6 months and assigned a score based on the clinical severity of dermatitis. Disease was scored by the following scale: 1 = red or dry skin in obvious areas with no hair loss; 2 = red, dry skin with alopecia on the head, ears may or may not show signs of necrosis; and 3 = hair loss extends to areas other than head, scale and crust formation (7).

T cell depletions
Anti-mouse CD4, CD8 and TCRß mAb antibodies were obtained from hybridomas GK1.5, Lyt2 and HB218 respectively (ATCC, Manassas, VA). Five-week-old CD18–/– PL/J N6 mice were injected i.p. with 100 µg of each antibody daily for 4 days, then every fourth day for 1 month for a total of 12 doses. Mice received a regimen of either all three antibodies (n = 8), anti-CD4 and anti-CD8 antibodies (n = 5), anti-CD4 antibodies (n = 5) or anti-CD8 antibodies (n = 5). Animals were observed twice weekly for the development of dermatitis. Thirteen age-matched, non-treated homozygous CD18 mutant PL/J mice were used as controls.

Immunohistochemistry
Skin sections were snap frozen in OCT compound, sectioned onto glass slides, fixed in absolute ethanol and glacial acetic acid, and washed in PBS. The slides were treated with 3% H2O2 to quench endogenous peroxidase activity. The slides were then blocked with rabbit serum for 20 min and incubated with either anti-CD4 or -CD8 rat anti-mouse antibodies (PharMingen, San Diego, CA). The slides were then incubated with biotinylated rabbit anti-rat antibody followed by avidin–horseradish peroxidase conjugate and with diaminobenzidine tetrahydrochloride using the Vectastain Elite ABC kit (Vector, Burlingame, CA) according to the manufacturer’s directions. The slides were counterstained with hematoxylin, dehydrated, and cover slipped with Permount mounting medium (Fisher Scientific, Pittsburgh, PA).

Flow cytometry
Peripheral blood was obtained by retro-orbital puncture under 3% methoxyflurane general anesthesia, blocked with anti-CD16/CD32 Fc antibody 2.4G2 and stained with either phycoerythrin (PE)-labeled CD3, PE-labeled CD8 or FITC-labeled CD4 (PharMingen, San Diego, CA). Erythrocytes were then lysed with ammonium chloride lysis buffer and washed twice with PBS. The leukocytes were fixed in paraformaldehyde and analyzed with a Becton Dickinson FACSCalibur (San Diego, CA) flow cytometer. Non-specific staining was determined using isotype-matched control antibodies. The mean number of positively staining cells in peripheral blood was calculated after subtracting out the non-specific background levels. The percent remaining cells was then determined by dividing the mean number of the positive cell counts for the treatment group by the counts obtained from a CD18–/– PL/J (control) mouse and multiplying by 100. For weeks 8, 10 and 15, only half of the mice in the CD4/CD8/TCRß group were evaluated.


    Results
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
The hallmark of CD18 deficiency in humans and cattle is increased susceptibility to infection (3,23,24). It has been suggested that several skin diseases such as guttate psoriasis can be the result of immunologic alterations influenced by bacterial infection (20,25,26). It is possible that the lowered CD18 expression in PL/J mice may predispose them to bacterial infections and result in the dermatitis phenotype. Previous microbiologic analyses by various culture and histologic staining techniques did not reveal the presence of pathogenic organisms, but could not rule out the influence of microorganisms in the pathogenesis of the disease (6). To evaluate the role of bacteria in the initiation and development of dermatitis, we cesarean derived CD18–/– (Itgb2tm1Bay) PL/J mice into flexible film isolators and raised them in a sterile environment. We found that homozygous CD18 mutant PL/J mice developed dermatitis with identical severity and histologic characteristics to that of standard microisolator-raised CD18–/– PL/J mice (Fig. 1). The time of onset of disease was also similar to that in our previous report and in mice raised in specific pathogen-free conditions in our normal colony (weeks ± SEM = 8.3 ± 0.4 for germ-free mice versus 10.2 ± 0.6 for specific-pathogen-free, P = 0.149; Fig. 2). These findings demonstrate that the skin disease is not caused by bacterial infection or by immunologic changes associated with bacterial infection, but rather is controlled primarily by lowered ß2 integrin expression and other PL/J loci.



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Fig. 1. Germ-free experiments. (A) Normal CD18+/+ PL/J skin (hematoxylin & eosin). (B) Skin from germ-free CD18–/– PL/J mouse. (C) Skin from non-germ-free CD18–/– PL/J mouse.

 


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Fig. 2. Age of disease onset for germ-free and T cell-depletion manipulations. Age of disease onset in weeks for untreated CD18–/– PL/J mutant mice, cesarean-rederived germ-free CD18–/– PL/J mutant mice, and CD18–/– PL/J mice depleted of CD4+, CD8+ and/or TCRß+ T lymphocytes at 5 weeks of age. *Significantly delayed disease onset compared to the other groups (P <= 0.01). Two mice in the CD4+/CD8+/TCRß+-depleted group and three mice in the CD4+/CD8+ did not develop dermatitis during the study period. Mice that did not develop disease were not included in the statistical analysis.

 
T lymphocytes are the primary inflammatory cells in the dermis and epidermis in CD18-deficient PL/J dermatitis in the early stages of the disease (6). To address the roles of T cells in the initiation and progression of skin disease in this model, we performed both adoptive transfer and T cell depletion analyses. Adoptive transfer of lymphocytes can induce or accelerate the development of disease in other models of inflammatory diseases, such as non-obese diabetic mice, experimental allergic encephalomyelitis and the C3H/HeJ mouse model of alopecia areata (2729). In the first series of experiments, we adoptively transferred splenocytes from affected CD18–/– PL/J mice into CD18+/– PL/J recipients treated with or without non-lethal irradiation. We found that no regimen of transferring CD18–/– splenocytes from affected mice could induce disease in CD18 heterozygotes, even though some recipients received 75 x 106 cells (data not shown).

Next, we transferred lymphocytes from CD18+/– PL/J mice into unaffected CD18–/– PL/J mice prior to the development of skin inflammation. Although there was no statistical difference in the age of onset, the clinical course of dermatitis was different when compared to untreated controls (Fig. 3). In these experiments, some of the recipient mice began to develop the initial signs of dermatitis similar to the control CD18–/– PL/J mice, but these mild lesions quickly resolved. This phenotype was much more pronounced in recipients that were non-lethally irradiated, with 100% of the mice (five of five) showing disease resolution. In unirradiated mice, only one out of four mice followed this pattern and the rest developed disease identical to the untreated controls.



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Fig. 3. Clinical course of dermatitis in adoptive transfer recipients compared to non-treated CD18–/– PL/J controls. CD18–/– PL/J mice were sublethally irradiated and injected with 8–10 x 106 splenocytes from CD18+/– PL/J mice. The injected mice developed mild dermatitis ~4 weeks after the adoptive transfers, but the disease resolved and did not return.

 
We next evaluated the specific roles of T lymphocytes in the initiation of skin disease using antibody-mediated T cell depletion. In the first experiment, we treated 5-week-old, unaffected CD18–/– PL/J mice with anti-CD4, -CD8 and -TCRß antibodies. These mice were observed twice weekly for age of onset and clinical course of dermatitis, and compared to untreated controls. CD18–/– PL/J mice depleted of mature T cells developed skin inflammation at a significantly later age than untreated –/– controls (mean ± SEM week of onset of T cell depleted mice = 23.9 ± 1.1 versus non-depleted mice = 10.2 ± 0.6, P < 0.001; Fig. 2). A representative 20-week-old T cell-depleted CD18–/– PL/J mouse and an age-matched non-treated CD18–/– PL/J control are shown in Fig. 4. Two additional depleted mice that had not developed disease were sacrificed for tissue collection on weeks 20 and 29. Skin sections from these mice were stained for CD4+ and CD8+ lymphocytes, and demonstrated a minimal presence of either cell type in the dermis or epidermis, a pattern similar to that observed in skin sections from normal CD18+/+ PL/J mice (Fig. 5). In contrast, skin sections from age-matched, non-treated CD18–/– PL/J mice revealed a marked infiltrate of both CD4+ and CD8+ lymphocytes in the dermis and epidermis (Fig. 5). These findings are consistent with a primary role for T cells in initiating the pathogenesis of dermatitis in this model. To evaluate the effectiveness of our T cell depletions in this experiment, we measured overall numbers of CD3+ expressing cells in peripheral blood (Table 1). This analysis showed that >75% of the circulating CD3+ T lymphocytes were depleted in mice up to 6 weeks following the initiation of treatment.



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Fig. 4. Lymphocyte depletions at 20 weeks. Twenty-week-old CD18–/– PL/J mouse treated with mAb against CD4+, CD8+ and TCRß+ T lymphocytes (left), and 20-week-old untreated CD18–/– PL/J mouse (right).

 


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Fig. 5. CD4+ and CD8+ T lymphocytes in treated and untreated mice. Immunohistochemical staining for CD4+ T lymphocytes in skin from a CD18+/+ PL/J mouse (A), a 20 week-old CD18–/– PL/J mouse treated with mAb against CD4+, CD8+ and TCRß+ T lymphocytes (B), and an untreated 20-week-old CD18–/– PL/J mouse (C). Immunohistochemical staining for CD8+ T lymphocytes in skin from a CD18+/+ PL/J mouse (D), a 20-week-old CD18–/– PL/J mouse treated with mAb against CD4+, CD8+ and TCRß+ T lymphocytes (E), and an untreated 20-week-old CD18–/– PL/J mouse (F).

 

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Table 1. Effectiveness (%) of the T cell depletions
 
We next performed in vivo lymphocyte depletions in 5-week-old CD18–/– PL/J mice using either CD4 or CD8 antibodies to remove these specific subsets of lymphocytes. We found that single depletion of CD4+ or CD8+ T lymphocytes did not prevent or prolong the onset of skin disease (Fig. 2, P = 0.837 and 0.895 respectively). In contrast, depletion of both CD4+ and CD8+ T lymphocytes resulted in a significant delay in the development of dermatitis. Two of the five mice developed disease significantly later than non-treated controls (mean ± SEM week of onset of CD4/CD8 depleted mice = 17.8 ± 2.5 versus non-depleted mice = 10.2 ± 0.6, P = 0.001), while another two had not developed disease by week 28 when the study was ended. The fifth mouse died at week 20 with no disease. Interestingly, four of the five CD4+ lymphocyte-depleted mice developed disease within 2 weeks of initiation of the depletions, suggesting that a population of disease-suppressing CD4+ T cells may be present and that the disease is driven by CD8+ T cells. However, CD8+ T cell-depleted mice developed dermatitis similar to non-treated controls (Fig. 2), suggesting that CD4+ cells may also mediate disease in this model. The effectiveness of these depletions was evaluated by using CD4+ or CD8+ antibody staining of peripheral blood lymphocytes (Table 1). In the single depleted mice, skin inflammation developed prior to the return of lymphocyte counts to wild-type levels. In mice depleted of both CD4+ and CD8+ T cells, disease onset was significantly delayed beyond 8 weeks post-treatment initiation, despite the return of both cell subset populations to near the levels observed in non-treated controls.


    Discussion
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 
CD18 mutant PL/J mice are a useful model for studying both the genetics and pathogenesis of inflammatory skin diseases such as psoriasis, atopic dermatitis and alopecia areata. In these studies we investigated the cellular mechanisms involved in initiation of this disease. We show that the development of inflammatory skin disease is not the result of bacterial infection, since germ-free CD18 mutant PL/J mice developed disease identical to that of mice in standard filtered cage housing. We also found, using in vivo T cell-depletion strategies, that this disease appears to be T cell mediated.

CD18 mutant PL/J mice depleted of both CD4+ and CD8+ T cells showed delayed disease onset, even after both T cell subsets had returned to near wild-type levels. Depletions of either CD4+ or CD8+ T lymphocytes in CD18 mutant PL/J mice, unlike depletion of both cell types, did not significantly delay the onset of disease. Interestingly, CD4 depletions resulted in a rapid onset of dermatitis in four of the five mice, suggesting that CD8+ T cells can efficiently mediate the initiation of disease. However, dermatitis also developed in the CD8+ T cell-depleted mice, suggesting there may be additional CD4+ T cells involved in the initiation of skin inflammation. Collectively, these findings suggest that both CD4+ and CD8+ T cells can mediate skin disease in CD18 mutant PL/J mice. Interestingly, similar functions of CD4+ and CD8+ T cells have been demonstrated in hapten-mediated allergic contact dermatitis, in which both T cell subpopulations can act as effector cells (30). In contrast to our findings, depletion of CD8+ T cells resulted in a reduced response (31,32).

These results, combined with our previous observations in the model, suggest that low-level expression of the ß2 integrins somehow alters T cell function in PL/J mice. However, the mechanisms by which these alterations occur, as well as the role of these adhesion molecules in this process, are not clear. It is possible that adhesion events mediated by the ß2 integrins in the thymus or periphery are altered by the CD18 mutation and result in the release of autoreactive T cells, the deletion of disease-suppressing regulatory T cells or both. LFA-1 interactions with ligands such as ICAM-1 appear to play a role in thymic selection and peripheral T cell activation and effector phenotype development, and it is possible that these processes are functionally altered in this model (33,34). Lowered expression of LFA-1 may affect thymocyte affinity or intracellular signaling during selection, resulting in the release of autoreactive T cells that normally would be eliminated.

Another possible mechanism may involve alterations in the development or activity of regulatory CD4+ T cells (35,36). Two different lines of evidence are consistent with this possibility. First, we observed the rapid onset of skin disease in the majority of CD18–/– PL/J mice following CD4+ T cell depletion. Second, we found that adoptive transfer of splenocytes from unaffected PL/J mice could slow the progression and ultimately ameliorate skin disease in CD18–/– PL/J recipients. Thus, these findings suggest that low-level expression of the ß2 integrins may lead to a deficiency in the numbers and/or functional activity of a population of CD4+ T cells that normally suppress the development of skin disease in PL/J mice, although this will require further study.

The ß2 integrins, especially LFA-1, also participate in lymphocyte co-stimulation and T cell signaling. Interaction between LFA-1 and ICAM-1 is sufficient to induce TCR-dependent proliferation of T cells and is required for optimal CD8+ T cell activation (37,38). LFA-1 interacts with the protein JAB1 to mediate AP-1 transcription and up-regulation of IL-2 expression (39,40). Lowered expression of LFA-1 and/or other ß2 integrin proteins may alter these signaling events, and this may ultimately lead to a pro-inflammatory response in skin in the presence of specific PL/J modifier alleles. In humans, LFA-1 interaction with ICAM-1 and ICAM-2 has also been shown to influence helper T cell polarization toward Th1 or Th2. Blocking LFA-1–ICAM-1 interactions diminishes Th1 differentiation and increases the production of the Th2 cytokines by 15- to 40-fold (41,42). Psoriasis in humans is dominated by a Th1 cytokine response, whereas atopic dermatitis is mediated by Th2 cytokines (11,43). Dermatitis in CD18-deficient PL/J mice, like psoriasis and atopic dermatitis in humans, may be the result of a Th1/Th2 cytokine imbalance.

Bacterial superantigens may cause some manifestations of psoriasis. It has been proposed that superantigen stimulation of T lymphocytes can induce cross-reactivity with skin antigens due to similar amino acid sequences in keratin and bacterial epitopes (22,44). Mice deficient in ß2 integrins may be more susceptible to bacterial colonization and infection on the skin, and subsequently be exposed to higher numbers of bacteria than wild-type mice. However, our derivation of the CD18 mutant PL/J mice into a germ-free environment demonstrated that this phenotype is not the consequence of bacterial superantigen stimulation.

In summary, dermatitis in CD18 mutant PL/J mice is an immune-mediated disease that is not dependent on infection with bacteria or other microorganisms. The disease appears to be mediated by both CD4+ and CD8+ T lymphocytes. Future work will focus on defining the ß2 integrin-dependent pathways that lead to alterations of T cell function and development of dermatitis in this model, as well as the potential role of these adhesion molecules in the pathogenesis of human inflammatory skin diseases.


    Acknowledgement
 
This work was supported by a grant to DCB from the Arthritis Foundation.


    Abbreviations
 
PE—phycoerythrin


    References
 Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 References
 

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