1 Salvatore Maugeri Foundation, IRCCS, Rehabilitation Institute of Pavia, Division of Nephrology and Haemodialysis 2 Division of Nephrology, IRCCS Ospedale Maggiore, Milano 3 Department of Biochemistry, University of Pavia 4 Biotechnology Research Laboratory, IRCCS Policlinico S. Matteo, Pavia 5 Department of Internal Medicine, University of Pavia 6 Research Laboratories, Department of Infectious Diseases IRCCS Policlinico S. Matteo, Pavia, Italy
Sir,
Renal involvement during chronic hepatitis C virus (HCV) infection may develop as part of the concomitant mixed (usually type II) cryoglobulinaemic syndrome, the so called cryoglobulinaemic nephropathy [1], or as HCV-associated membranoproliferative glomerulonephritis [2], in which patients may be non-cryoglobulinaemic and inconstantly present typical mixed cryoglobulinaemic symptoms. Although the morphological characteristics are very similar, it is still a matter of debate whether the two entities have different pathogenetic mechanisms. To further discuss the role of HCV infection in glomerulonephritis and cryoglobulinaemia, we would like to report on a case of HCV-associated membranoproliferative glomerulonephritis, with the histological features of a cryoglobulinaemic pattern, in which cryoglobulins were not detected at the time of renal biopsy. Cryoglobulin appeared in small amounts during the follow-up; moreover cryoprecipitate analysis did not show the usual mixed pattern, but fit in with type I (IgMk) cryoglobulinaemia.
Case.
A 63-year-old woman was admitted to our unit for hypertension and microscopic haematuria. She was asymptomatic and physical examination was unremarkable. Laboratory investigation showed normal serum creatinine (1.1 mg/dl), mild anaemia (11.6 g/dl), increased erythrocyte sedimentation rate (ESR), dysmorphic erythrocyturia, and no proteinuria. C4 was slightly reduced, antinuclear antibodies and cryoglobulins were absent, and HCV antibodies were not checked at that time. She was discharged on nifedipine therapy.
Three years later the patient was re-admitted because of weakness, ankle oedema and poor blood pressure control. Laboratory investigation showed serum creatinine 1.3 mg/dl, AST 114 U/l, ALT 142 U/l, haemoglobin 10 g/dl; in urinalysis erythrocyturia persisted and proteinuria appeared (1.93 g/24 h). C4 was confirmed in the low-normal range, cryoglobulins were not found, but rheumatoid factor was strongly positive (1580 U/ml, normal up to 14). Antibodies to HCV were present, together with viraemia, whereas HBV markers were negative. Renal biopsy showed diffuse membranoproliferative glomerulonephritis with severe infiltrate of mononuclear inflammatory cells in the tuft and some capillary loops occluded by proteinaceous material, i.e. pseudothrombi. Immunofluorescence staining detected IgM, C1q and C3 in the mesangium and capillary wall. Electron microscopy revealed segmental subendothelialmesangial electron-dense deposits, with a vaguely fibrillary structure. The biopsy data were highly suggestive of cryoglobulinaemic membranoproliferative glomerulonephritis. Liver biopsy was unremarkable. Cryoglobulins were re-checked, but not found. The patient was given a 6-month treatment with prednisone 1 mg/kg for 1 month and then gradually tapered, and -interferon 3 MU three times weekly. Hypertension control needed a five-drug regimen (ACE-inhibitor, thiazide, lacidipine, clonidine and doxazosin), while anaemia required erythropoietin.
At the end of the treatment, liver enzymes normalized, proteinuria decreased to 0.4 g/24 h, serum creatinine increased to 1.7 mg/dl, viraemia and strong positivity for rheumatoid factor persisted and for the first time cryoglobulins were found. Cryocrit was 1%, made up of an IgMk monoclonal immunoglobulin (Figure 1). Interestingly the IgM, purified as previously reported [3], showed no rheumatoid activity, but had a low affinity/activity against HCV. Therefore the rheumatoid activity observed in serum was caused by cryo-soluble polyclonal antibodies. The purified protein was sequenced: the N-terminal sequence of the heavy chain was Ala-Val-Gln-Leu-Val-Glu-Ser-Gly-Gly, whereas the N-terminal light-chain sequence was Ala-Ile-X-Met-Thr-Gli-... . The N-terminal amino acid sequence of the heavy and light chains confirms the homogeneity of this material and the amino acid sequence assigns the light chain to class I and the heavy chain to class III. During follow-up renal function remained slightly impaired. IgMk cryoglobulins were confirmed in small amounts and the paraprotein also appeared in serum electrophoresis. HC viraemia was still present, classified as 2a/c genotype.
|
Comment.
Diagnosis of HCV-related cryoglobulinaemic syndrome was supported in our patient by the presence of many features, including the characteristic picture of cryoglobulinaemic glomerulonephritis. Weakness, oedema, hypertension and anaemia were present, purpura and arthralgias were lacking; however, the most surprising finding was the absence of serum cryoglobulins when the full-blown syndrome developed. A circulating monoclonal cryoglobulin (IgMk) was detected in small amounts 6 months later. Negative screening for serum cryoglobulins in patients with HCV-associated nephritis was first reported by Johnson et al. [2]. However, the lack of cryoglobulins in serum does not exclude a role in inducing glomerular damage. As a matter of fact properties for in vitro cryoprecipitation may be shared, but not correspond entirely, with those required for accumulation in glomeruli. Moreover, cryoglobulins may be produced at a low rate and be rapidly trapped owing to their affinity with the glomerular structures.
Concerning the finding of a single monoclonal component in the cryoprecipitate of our patient, it is worth noting that the unusual association of type I cryoglobulinaemia and membranoproliferative glomerulonephritis has so far been reported only in eight cases (reviewed in [4]), often associated with lymphoproliferative disease. Moreover, in a large series of patients with cryoglobulinaemic glomerulonephritis, cryoprecipitate was seldom classified as type I (4% of cases) [5]. On the other hand, data on the prevalence of anti-HCV antibodies in patients with type I cryoglobulinaemia are scanty: Agnello et al. [6] found no anti-HCV antibodies or HCV-RNA in nine cases with type I cryoglobulinaemia and Waldenström's disease or myeloma. Therefore, a pathogenic link between HCV infection and type I cryoglobulinaemia still remains unproven.
The low affinity/activity against HCV of the monoclonal IgMk we found in the cryoprecipitate seems to support a role of the viral infection in the production of the cryoprecipitable monoclonal immunoglobulin. However, the pathogenesis of HCV-associated cryoglobulinaemic glomerulonephritis remains so far to be elucidated. The virus may activate B lymphocytes to produce IgG and IgM, the so-called mixed cryoglobulins, which accumulate in the glomeruli owing to their properties. Alternatively, nephritis may be induced by the deposition of HCV/anti-HCV antibody complexes, irrespective of cryoglobulin formation.
Although we were unable to demonstrate the presence of HCV antigens in renal biopsy, the low affinity/activity against HCV of the cryoprecipitate might fit in with this last pathogenetic hypothesis. As an alternative hypothesis, HCV infection in our patient might have elicited the production of the monoclonal immunoglobulin which deposited in the glomeruli due to a peculiar affinity with those antigenic structures. This pathogenetic hypothesis is supported by the experimental study carried out by Fornasieri et al. [7] in which they succeeded in inducing cryoglobulinaemic membranoproliferative glomerulonephritis in mice after an injection of human IgMk isolated from type II cryoglobulinaemic patients.
In conclusion, the case we report seems to strengthen the idea that HCV may trigger multiple potential nephritogenic pathways, among which that associated with the production of type I cryoglobulins should also be taken into account.
References