Human rheumatoid factor cross-idiotypes. III. Bla monoclonal rheumatoid factor, prototype of the BLA cross-idiotype group, has distinct kappa chains related to the V kappa III subgroup and VH4 heavy chains

B cell proliferation, somatic hypermutation, class switch recombination, and autoantibody production in ectopic lymphoid tissue in murine lupus

Intraperitoneal exposure of nonautoimmune mice to 2,6,10,14-tetramethylpentadecane (TMPD) causes lupus and the formation of ectopic lymphoid tissue. Although associated with humoral autoimmunity, it is not known whether Ab responses develop within ectopic lymphoid tissue or if B cells only secondarily migrate there. We show that ectopic lymphoid tissue induced by TMPD not only resembles secondary lymphoid tissue morphologically, but it also displays characteristics of germinal center reactions. Proliferating T and B lymphocytes were found within ectopic lymphoid tissue, activation-induced cytidine deaminase was expressed, and class-switched B cells were present. The presence of circular DNA intermediates, a hallmark of active class switch recombination, suggested that class switching occurs within the ectopic lymphoid tissue. Individual collections of ectopic lymphoid tissue ("lipogranulomas") from the same mouse contained different B cell repertoires, consistent with local germinal center-like reactions. Class-switched anti-RNP autoantibody-producing cells were also found in the lipogranulomas. Somatic hypermutation in the lipogranulomas was T cell-dependent, as was the production of isotype-switched anti-Sm/RNP autoantibodies. Thus, ectopic lymphoid tissue induced by TMPD recapitulates many of the functional characteristics of secondary lymphoid tissue and contains autoantibody-secreting cells, which may escape from normal censoring mechanisms in this location.

The aetiology of mixed cryoglobulinaemia associated with hepatitis C virus infection

A strong association of hepatitis C infection (HCV) with 'essential' mixed cryoglobulinaemia has been established. The demonstration of HCV in Type II mixed cryoglobulins with monoclonal rheumatoid factors (mRF) that bear the WA crossidiotype has lead to the hypothesis that mixed cryoglobulins result from chronic stimulation by HCV-lipoprotein of a population of XId WA+B-1a cells. The reactivity of WA IgM initially produced is with the HCV-self antigen complex with RF activity resulting secondarily from the pausi-mutational process accompanying the T cell independent process. This benign proliferation progresses by multi step mutations to malignancy in a minority of patients. The implications of the hypothesis for understanding the physiology of certain natural auto antibodies and for therapeutic intervention in this disease are discussed.

Human rheumatoid factor cross-idiotypes. IV. Studies on WA XId-positive IgM without rheumatoid factor activity provide evidence that the WA XId is not unique to rheumatoid factors and is distinct from the 17.109 and G6 XIds

The WA cross-idiotype (XId) is the major XId among human monoclonal rheumatoid factors (mRF) and is almost always associated with the light (L) chain XId, 17.109, and the heavy (H) chain XId, G6. A cell line, 35G6, was cloned that bears the WA XId, but shows no reactivity with immunoglobulin G (IgG) and is negative for the 17.109 and G6 XIds. The 35G6 L chain appears to be derived from the same VKIII-JKI genes as most WA mRFs L chains. In contrast to the WA mRFs H chains in which VH1 genes are used, the 35G6 IgM expresses a VH3 gene. Sequence comparisons with other WA XId-positive mRF suggested several common structural features that may be related to the WA XId and differences that may relate to lack of IgG reactivity. Cells similar to 35G6 have previously been described in pokeweed mitogen-stimulated cell lines of peripheral blood lymphocytes from normal individuals and patients with rheumatoid arthritis and type II mixed cryoglobulinemia. These observations were confirmed, and in addition, it was shown that the majority of WA XId-positive cells in these cultures were negative for the 17.109 and G6 XIds. The presence of the WA XId in the absence of IgG reactivity suggests that the WA XId is more directly associated with an antigen specificity other than IgG, and its association with RF activity may be incidental. It is postulated that these WA XId-positive RF-negative antibodies may serve a physiologic role as natural antibodies to a pervasive pathogen, and that IgG reactivity is a consequence of somatic diversification accompanying proliferation of the WA XId-positive RF-negative cell.

Hepatitis C virus infection and mixed cryoglobulinemia: a striking association

The high frequency of liver involvement in cryoglobulinemia is well established. Although both etiology and pathogenesis have remained so far undefined, recent studies suggest an association of mixed cryoglobulinemia with hepatitis C virus infection. To explore this hypothesis further, we assessed the prevalence of hepatitis C virus antibodies and RNA in a large group of patients, including: (1) 35 patients with cryoglobulinemia without clinical evidence of liver involvement (group 1), (2) 15 patients with symptomatic cryoglobulinemia associated with chronic liver disease (group 2) and (3) 12 patients with asymptomatic cryoglobulinemia associated with chronic liver disease (group 3). Anti-hepatitis C virus antibodies were detected by a second-generation enzyme-linked immunosorbent assay and third-generation immunoblot (SIA Prototype RIBA), whereas the polymerase chain reaction was used for the detection of viral RNA. Anti-hepatitis C virus antibodies, as detected by enzyme-linked immunosorbent assay, were demonstrated in 21 (60%) patients from group 1, 11 (73.3%) from group 2 and 10 (83.3%) from group 3. The immunoblot identified as positive 3 further patients in group 1 (giving a prevalence of 68.6%) and all patients in groups 2 and 3. Hepatitis C virus RNA was demonstrated in cryoprecipitates from 21 of 24 immunoblot-positives and from 6 of 11 immunoblot-negatives, indicating an actual active viral replication in 77.1% of group 1. This was also found in 13 (86.7%) and 10 (83.3%) cryoprecipitates of groups 2 and 3, respectively. Type II cryoglobulinemia was the prevalent form in group 1 (88.6%) and group 2 (73.3%), whereas type III was found in group 3 (58.3%) and in 26.7% of group 2.(ABSTRACT TRUNCATED AT 250 WORDS)

A role for hepatitis C virus infection in type II cryoglobulinemia

BACKGROUND

Type II cryoglobulinemia is a vasculitis characterized by cryoglobulins consisting of complexes of polyclonal IgG and monoclonal IgM rheumatoid factors. The cause of these immune complexes is unknown, though both the hepatitis B (HBV) and C (HCV) viruses have been suspected.

METHODS

We studied 19 patients with Type II cryoglobulinemia for markers of HCV and HBV infection. Quantitative HCV antibody and RNA studies were performed on whole serum, cryoprecipitates, and supernatants.

RESULTS

Eight patients (42 percent) had HCV antibodies, and 16 (84 percent) had HCV RNA: Of the 19 patients, 5 (26 percent) had HBV markers, but only 1 had evidence of active HBV infection. Control serum samples from nine patients with Type I cryoglobulinemia were negative for HCV antibody and HCV RNA: There was a close, although not exclusive, association of one type of rheumatoid factor (WA) with HCV RNA: HCV antibody and HCV RNA were concentrated approximately 10-fold and 1000-fold, respectively, in the Type II cryoglobulins examined.

CONCLUSIONS

Type II cryoglobulinemia is strongly associated with concomitant HCV infection and a high rate of false negative serologic tests. HCV virions and HCV antigen-antibody complexes are concentrated in the cryoprecipitates, most commonly in association with the WA type of rheumatoid factor, suggesting a role for HCV in the pathogenesis of mixed cryoglobulinemia.

Complete amino acid sequence of the variable regions of two highly related heavy and light chains of human IgG (SFL) and IgM (RIV) rheumatoid factors

The complete amino acid structure of the variable regions of two monoclonal human rheumatoid factors (RF), antibodies that bind to the Fc portion of IgG, is presented. Although these RFs are of different isotypes, IgG (SFL) and IgM (RIV), they are highly related. They probably derive from the same KIII light chain variable region used, but the heavy chains are derived from genes of the VHIII family that are probably evolutionarily related. An analysis of the level of somatic mutation reveals that antigen selection was probably involved in the maturation of these clones. These antibodies, although highly related, are not merely IgM to IgG switch variants which occurred independently in different individuals. Little is currently known about the structure of IgG RFs and this study indicates that the level of somatic mutation of SFL is similar to other autoantibodies or antiviral antibodies of the IgG isotype.