Human rheumatoid factor crossidiotypes. I. WA and BLA are heat-labile conformational antigens requiring both heavy and light chains

The Kunkel legacy and hepatitis C virus infection

In commemoration of Henry Kunkel's 100th birthday, the effect of his legacy on the investigation of hepatitis C virus is recounted. The delineation of a major cross-idiotype (WA) among patients with essential mixed cryoglobulinemia led to the discovery that HCV was the etiologic agent for this disease. Studies of the cryoglobulins led to the discovery that WA RF reacted specifically with HCV-VLDL like particles that on electronmicroscopy and binding studies appeared to be the virion within a lipid shell. This particle mediates cell entry via LDLr and may serve to avoid the immune response by masking the virion. In addition, the WA B cell may be a prognostic marker for cutaneous vasculitis and B cell malignancy in HCV-infected patients. In commemoration of Henry Kunkel's 100th birthday, this is an account of how his legacy had a role in the investigation of hepatitis C virus (HCV) infection. There is a bit of a historical basis for the legacy of this great immunologist having a role in virology. He began his research career studying hepatitis. Later he worked with HCV in his studies of mixed cryoglobulins although he didn't know it at the time. There may also have been a Kunkel historical basis for why he accepted me as fellow in his laboratory considering that my credentials paled in comparison with those of the fellows and PhD students in his laboratory. Like Henry I was drafted into the Navy following my internship, I had had minimal research experience in medical school and only one minor publication, and I had a passion for clinical investigation. It may have been fortuitous that while on active duty at the Bayonne NJ Naval Base I visited Henry Kunkel in my Navy uniform and told him I was interested in studying SLE. I did not know at the time the dramatic role the Navy had played in his career or that one of his major training goals was to teach MDs to use clinical observation as a focus for delineating disease mechanisms in the laboratory. When I started work in the laboratory on discharge from the Navy, the first thing he told me was that it took five years to make a clinical investigator so I might as well get a Rockefeller University PhD while working in his laboratory. I was sure I would leave the laboratory after two years so I declined his offer. I did not leave until six years later!

Somatic hypermutations confer rheumatoid factor activity in hepatitis C virus-associated mixed cryoglobulinemia

OBJECTIVE

Hepatitis C virus (HCV) is the most frequent cause of mixed cryoglobulinemia (MC), which is characterized by endothelial deposition of rheumatoid factor (RF)-containing immune complexes and end-organ vasculitis. MC is a lymphoproliferative disorder in which B cells express RF-like Ig, yet its precise antigenic stimulus is unknown. We have proposed that IgG-HCV immune complexes stimulate B cell expansion and somatic hypermutation (SHM)-induced affinity maturation in part via engagement of an RF-like B cell receptor. This study was undertaken to test the hypothesis that SHM augments RF activity.

METHODS

RFs cloned from single B cells from 4 patients with HCV-associated MC (HCV-MC) were expressed as IgM, IgG, or IgG Fab. Selected Ig were reverted to germline. RF activity of somatically mutated Ig and germline-reverted Ig was determined by enzyme-linked immunosorbent assay.

RESULTS

Ig with SHM had RF activity, with the preference for binding being highest for IgG1, followed by IgG2 and IgG4, and lowest for IgG3, where there was no detectable binding. In contrast, reverted germline IgG exhibited markedly diminished RF activity. Competition with 1 μg/ml of protein A abrogated RF activity, suggesting specificity for IgG Fc. Swapping of mutated heavy-chain pairs and light-chain pairs also abrogated RF activity, suggesting that context-specific pairing of appropriate IgH and Igκ, in addition to SHM, is necessary for RF activity.

CONCLUSION

SHM significantly contributes to RF activity in HCV-MC patients, suggesting that autoreactivity in these patients arises through antigen-dependent SHM, as opposed to nondeletion of autoreactive germline Ig.

Hepatitis C virus and other flaviviridae viruses enter cells via low density lipoprotein receptor

Endocytosis of the Flaviviridae viruses, hepatitis C virus, GB virus C/hepatitis G virus, and bovine viral diarrheal virus (BVDV) was shown to be mediated by low density lipoprotein (LDL) receptors on cultured cells by several lines of evidence: by the demonstration that endocytosis of these virus correlated with LDL receptor activity, by complete inhibition of detectable endocytosis by anti-LDL receptor antibody, by inhibition with anti-apolipoprotein E and -apolipoprotein B antibodies, by chemical methods abrogating lipoprotein/LDL receptor interactions, and by inhibition with the endocytosis inhibitor phenylarsine oxide. Confirmatory evidence was provided by the lack of detectable LDL receptor on cells known to be resistant to BVDV infection. Endocytosis via the LDL receptor was shown to be mediated by complexing of the virus to very low density lipoprotein or LDL but not high density lipoprotein. Studies using LDL receptor-deficient cells or a cytolytic BVDV system indicated that the LDL receptor may be the main but not exclusive means of cell entry of these viruses. Studies on other types of viruses indicated that this mechanism may not be exclusive to Flaviviridae but may be used by viruses that associate with lipoprotein in the blood. These findings provide evidence that the family of LDL receptors may serve as viral receptors.

Predictors of Long-Term Response to High-Dose Interferon Therapy in Type II Cryoglobulinemia Associated With Hepatitis C Virus Infection

We have prospectively studied patients with type II cryoglobulinemia since 1985 to assess the efficacy of treatment with interferon-α at cumulative doses ranging from 234 to 849 MU. In the present study we retrospectively evaluated in this cohort parameters associated with complete response to therapy in 31 consecutive patients with type II cryoglobulinemia associated with hepatitis C virus (HCV) infection. Prevalence of complete response of cryoglobulinemia (disappearance of symptoms and signs of vasculitis and decrease of cryocrit below 10% of the initial value) was 62%, with a median response duration of 33 months and a range of 3 to 100 months. Three patients were putatively cured, as they remained in complete remission for more than 5 years off therapy. Eighteen patients (58%) had liver disease evidenced by histopathology and/or raised transaminase levels. Prevalence of normalization of transaminase levels was 100%, with a median response duration of 36 months. Relapse of hypertransaminasemia occurred in 100% and 8% of patients receiving less than or greater than 621 MU, respectively. By logistic regression analysis, the only pretherapy parameter that associated significantly (P = .0393) with complete response of cryoglobulinemia was the solitary anti-C22 (HCV core) antibody pattern, which was observed in 29% of patients. Association with older age and low cryocrit approached statistical significance (P = .06), while no significant correlations were found with serum IgM levels, duration of disease, HCV genotype, NS5a gene mutations, liver histology, HLA-DR phenotype, or WA cross-idiotype. Complete responses were also associated, on univariate statistical analysis, with low pretherapy HCV viremia. Responses were accompanied by decrease of viremia, of anti-HCV antibody levels and cryocrit. The usefulness of a high dose regimen is underscored by the higher rates of sustained responses of cryoglobulinemia and transaminase levels compared with previous studies.

The etiology and pathophysiology of mixed cryoglobulinemia secondary to hepatitis C virus infection

The strong association of HCV infection with MC-II and the selective concentration of the virus with the WA mRF in the cryoglobulins are compelling suggestions that the virus is directly involved in production of the mRF and the pathophysiology of MC-II. There is, however, only limited data on HCV involvement in both processes. In cutaneous vasculitis, which is the most prevalent clinical feature of the disease, there is evidence that complexes of HCV, mRF and IgG are formed in situ from components of the cryoglobulins that are present in the blood in a dissociated state. It is postulated that local factors, cooling and stasis predispose to formation of these lesions in the lower limbs. However, since cutaneous vasculitis does not correlate with cryoglobulin levels and may not be induced by cold challenge, other factors may be involved. In particular, the conditions which activate the vascular endothelial cells, leading to the leukocytoclastic vasculitis, require delineation. In contrast to cutaneous vasculitis, HCV RNA has not been prominently detected in immune complexes in MPGN lesions and has not been detected at all in the peripheral neuropathy lesions. These preliminary observations suggest that different pathophysiological processes are involved in for these lesions than in cutaneous vasculitis. From the correlation of remission of disease with decreased cryoglobulinemia and viremia in treated patients with MC-II, and from immunohistological data on the hepatitic lymphoid follicles in MC-II (see chapter 7), it appears that an antigen-driven benign proliferation of B cells is responsible for production off mRF and cryoglobulinemia. New findings have suggested that one mechanism for developing mixed cryoglobulinemia may be that HCV-VLDL complexes that contain apo E2 are poorly endocytosed by the LDLR, which may be a major route of entry of the virus to the cell; persistence of the complexes in the circulation may then stimulate mRF production. This new hypothesis is based only on initial in vitro observations and require independent confirmation and validation in vivo. From indirect clinical evidence it has also been postulated that mRF in some patients may limit the cytopathology in MC-II, resulting in a lower prevalence of cirrhosis in these patients. These findings suggested another hypothesis, which is that the mRF prevents spread of infection to hepatocytes and other permissive and nonpermissive cells by blocking endocytosis of HCV-VLDL complexes by the LDLR. Furthermore, data on the composition of cryoglobulins, the molecular composition of WA mRF and the characterization of monoclonal B cells in the liver of patients with MC-II (see chapter 7) suggest that a specific population of B cells may be involved in the host response to HCV infection. These are B cells that proliferate with little or no somatic mutations of the immunoglobulin genes, are self-replicating, are stimulated by self antigens in a T cell-independent manner and bear the CD5 marker. The proliferation of this B cell population may be the host's response to the attempt by the virus to circumvent the immune response by complexing with host lipoproteins. It is proposed that HCV complexed to VLDL is the antigen that directly stimulates the proliferation of these primordial type B cells. Testing of these hypotheses may produce insights not only into the etiology of mixed cryoglobulinemia but possibly into the mechanisms by which HCV circumvents the immune response and established chronic infection.

Mixed cryoglobulinemia as a model of systemic vasculitis

Leukocytoclastic vasculitis is the dominant lesion of mixed cryoglobulinemia (MC). The high prevalence of antibodies to hepatitis C virus (HCV) in association with the higher concentration of HCV RNA genomic sequences in the cryoglobulins suggests a close relationship between MC and HCV infection and strongly supports the view that this virus plays a key role in causing vascular damage. Analysis of the composition of immune complexes (ICs) provides evidence that cryoglobulins include virions mostly bound to IgG that is specifically reactive with HCV-related proteins, which in turn are crosslinked by monoclonal IgM with rheumatoid factor (RF) activity, frequently bearing the WA crossidiotype (XId). This structure is similar (if not identical) to that of circulating ICs from HCV-infected patients without cryoglobulins, suggesting that the virus may be directly responsible for the production of WA RF. Evidence for the role of circulating cryoproteins in the pathogenesis of cutaneous and renal vasculitis stems from the demonstration of HCV-related proteins and/or HCV RNA genomic sequences in the vessel wall of patients with MC. Our data indicate that endothelial cells are fully susceptible to infection by and replication of HCV, and support the contention that they serve as sufficient targets for the binding of HCV proteins expressed on the cell surface to serum immunoglobulins. The in situ demonstration of IgM RF WA XId adds further evidence that RF of the WA group participates in the development of vasculitis and probably stabilizes the binding of IgG antibodies. Lymphocytes may be crucial in the infection of endothelial cells by acting as a circulating viral reservoir. After encouraging initial results, controlled trials have defined the substantive efficacy of IFN-alpha in the treatment of MC. A response of IFN can be achieved in more than 50% of patients and includes improvement of cutaneous vasculitis and renal function. This clinical response is accompanied by a reduction in hepatitis C viremia, serum cryoglobulin concentration, and IgM RF synthesis. However, almost 80% of responders eventually have a clinical and biochemical relapse. Additional studies are required to improve the outcome and extension of this therapy, define the best candidates, and indicate the situations in which it is needed.

Rheumatoid factor in the serum of hepatitis C virus-infected patients: an increase in the titre during cold storage

Storage of serum at 4 degrees C elevated the titre of rheumatoid factor (RF) as measured by nephelometry with IgG-coated latex in 12 of 38 specimens positive for hepatitis C virus. Increased RF following cold storage was not detected in HCV-negative sera. Most of the sera showing the cold-dependent elevation of RF had decreased complement hemolytic activity (CH50) after the cold storage. The RF titre elevated by cold storage decreased to the level of fresh serum by the addition of guinea pig serum as a complement supplement in a dose-dependent fashion. Thus, in the serum of some HCV-infected patients, the affinity of RF appears to be weak, and the binding between the RF and IgG coated on latex may be inhibited by the complement components of fresh serum.

Mixed cryoglobulinemia secondary to hepatitis C virus infection

Mixed cryoglobulinemia is a systemic vasculitis with clinical manifestations ranging from the characteristic benign-appearing syndrome of palpable purpura, arthrologies, and fatigue to severe vasculitis involving vital organs. A strong association of the disease with hepatitis C virus infection and the demonstration of the specific concentration of the virus in the cryoglobulins have implicated hepatitis C virus in the etiopathogenesis of the disease. The increase in illicit intravenous drug use in the past 30 years seems to have raised the occurrence in the United States of this once uncommon disease and changed the demographics: there seem to be more male intravenous drug users in their forties with the disease than women without risk factors for hepatitis C virus infection in their fifties and sixties. Pathogenesis, therapy, and the hypothesis on the etiologic role of hepatitis C virus are reviewed, and the implications of recent studies and new concepts for treatment of this often benign-appearing but deceptive and potentially life-threatening disease are discussed.

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.

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.

Inheritance of monoclonal rheumatoid factor cross-reactive idiotypes in primary Sjögren's syndrome (pSS). Comparative studies of a rabbit polyclonal anti-idiotype and 17109 monoclonal anti-idiotype

A comparison of the presence of two idiotypes, one identified by a rabbit polyclonal antiidiotypic antibody, first found on a cryoprecipitable IgM chi rheumatoid factor (RF) from an SS patient (3rd SS) and the 17109 idiotype, identified by a monoclonal antibody was performed in 106 sera and eight minor salivary gland biopsies of Sjögren's syndrome (SS) patients and 125 sera from age-sex matched normal controls. Of 106 of SS patients' sera 36 had immunoglobulins positive for the 3rd SS idiotype. 17109 activity was more prevalent in SS patients positive for the polyclonal anti-idiotype 3rd SS, than those with negative idiotype (9/36 VS 2/70 chi 2 = 12.53 P less than 0.005). Cross inhibition studies, however, revealed that the polyclonal anti-idiotype binding was not inhibited by the 17109 moAb. 3rd SS and 17109 anti-idiotypes were reacted with immunoglobulins in the serum of 3.5% and 1.7% of normal human sera respectively. Immunohistologic studies demonstrated that 4/8 and 2/6 minor salivary gland biopsies had infiltrating plasma cells containing immunoglobulins bearing the 3rd SS and the 17109 idiotypes, respectively. The inheritance of both idiotypes was investigated in sera of 4 SS kindreds. In two kindreds with 3rd SS positive probands, the idiotype was detected in 3 first degree relatives of the same generation. 17109 activity was detected in the serum of a sister of the positive proband who had a high RF titer. These results suggest that the 17109 moAb recognizes a different epitope of that of the 3rd SS. The idiotypes of monoclonal RFs are not inherited and probably are produced by plasma cells infiltrating the labial minor salivary glands of SS patients.

The major rheumatoid factor cross-reactive idiotype is dominantly expressed by Staphylococcus aureus Cowan strain I-activated CD5+ control B cells

Some seropositive (RF+) and seronegative (RF-) rheumatoid arthritis (RA) patients selectively express high concentrations of the major RF cross-reactive idiotype (RCRI) in their sera and generate high frequencies of RCRI+ pokeweed mitogen (PWM)-induced plasma cells from their peripheral blood mononuclear cells (PBM). To determine if normal individuals can express RCRI in vitro, B cells from controls were activated with Staphylococcus aureus Cowan strain I (SAC) bacteria to identify RCRI and RF production. In addition, we studied the relationship of RCRI expression with the subset of B cells bearing CD5. Control CD5+ B cells are responsible for RCRI expression following SAC activation. We also observed that RCRI is dominantly expressed by control SAC-induced B cells in frequencies comparable to that expressed by some RA and juvenile rheumatoid arthritis patients' PBM activated by PWM. Therefore, the frequency of RCRI+ B cells in control and arthritis patients' PBL may be similar, or the selection and/or regulation of RCRI+ B-cell expression in vitro and in vivo may be different in arthritis patients compared to normal individuals.

Hidden rheumatoid factor and Wa idiotype expression in juvenile rheumatoid arthritis

The major rheumatoid factor cross-reactive idiotype, which was defined by prototypic monoclonal IgM rheumatoid factors from Waldenstrom's macroglobulinaemia patient Wa, is present on 60% of all monoclonal IgM RF paraproteins. One-third of patients with juvenile rheumatoid arthritis (JRA), who are seronegative for classic IgM rheumatoid factor (RF), express the Wa idiotype in high titre in their sera. To determine if the Wa idiotype is present on hidden rheumatoid factors in JRA patient sera, we studied hidden RF expression by both ELISA and haemolytic assay techniques. The majority of JRA sera with increased concentrations of the Wa idiotype did not have increased RF activity nor hidden RF activity. In some JRA patients, the Wa idiotype may be expressed on a parallel set of immunoglobulin molecules, related to RFs, but lacking the ability to bind to IgG.

Expression of the major rheumatoid factor cross-reactive idiotype in pediatric patients with systemic lupus erythematosus

Rheumatoid factor cross-reactive idiotype (RF-CRI) is expressed in high concentrations in the sera of some patients with rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA). To determine if RF-CRI is specifically expressed in rheumatic disease or if it is secondary to polyclonal B-cell activation, we examined sera of 23 children with SLE, 16 adolescents with infectious mononucleosis (IM), and age-matched pediatric controls for RF-CRI expression. Concentrations of RF-CRI in serum, determined by an inhibition ELISA, were 24 +/- 17 micrograms/ml (mean +/- SD) in 25 normal children, 31 +/- 17 in 16 young adults with IM, and were significantly increased, 70 +/- 80 micrograms/ml, in the 23 children with SLE (p less than 0.036). Eleven of 23 SLE patients had serum RF-CRI greater than the mean +/- 2 SD for normal children. Ten of 23 SLE sera contained IgM rheumatoid factor (RF) activity. One patient with IM had a borderline elevated RF-CRI level, and 5 IM patients had RF in their sera. The serum IgM concentrations in sera were: SLE (192 +/- 93 mg/dl) and IM (234 +/- 77 mg/dl) sera. These levels were significantly elevated compared to controls (132 +/- 44 mg/dl), p less than 0.031 for SLE and p less than 0.001 for IM, suggesting that polyclonal activation of B cells was present in SLE and IM patient groups. Increased expression of RF-CRI in the SLE patients correlated directly with high titer anti-DNA antibody values (r = 0.3965, p less than 0.05) and RF activity when human IgG (r = 0.5026, p less than 0.05) was used as the RF binding substrate and inversely with serum C3 levels (r = 0.3925, p less than 0.05). RF-CRI expression did not correlate with RF that bound rabbit (r = 0.3123, p greater than 0.05). Increased serum RF-CRI expression is not a result of polyclonal B-cell activation. RF-CRI may be selectively up-regulated in patients with SLE.

Expression of large quantities of rheumatoid factor major cross-reactive idiotype in the serum of adults with seropositive rheumatoid arthritis

We quantified rheumatoid factor cross-reactive idiotype (RF-CRI) in whole serum from RF+ rheumatoid arthritis (RA) patients, using an inhibition enzyme-linked immunosorbent assay which is not affected by the presence of IgG. Serum from 16 RF+ RA patients contained 2-252 micrograms/ml RF-CRI (geometric mean */divided by SD 20.8 */divided by 5.2), while serum from 11 normal adults contained 1-16 micrograms/ml RF-CRI (geometric mean */divided by SD 3.9 */divided by 2.3). Serum from 8 of the RF+ RA patients contained RF-CRI at concentrations more than 2 standard deviations above the geometric mean in the normal subjects (greater than 21 micrograms/ml). Our results indicate that some RF+ RA patients express high concentrations of RF-RCRI and immunoglobulin molecules that express the RF-CRI may not be RF.

Stability of monoclonal antibody-defined epitopes

Epitope instability can limit the applications of monoclonal antibody (mAb) technology in laboratory and clinical research. We exposed a group of representative antigens on human hepatocellular carcinoma (HCC) cells to physiochemical insults to study epitope stability as measured by mAb immunoreactivity. Each epitope was found to have a unique pattern of instability which serves to biophysically characterize the antigen and defines the conditions to which the antigen can be exposed during laboratory and clinical investigations. Individual antigens were found to be unstable within a surprisingly well defined window of solvent polarities while being stable on either side of that window. Several antigens were observed to be unstable when exposed to transient changes in pH. When a critical temperature between 42 degrees C and 65 degrees C was achieved, epitopes which were thermosensitive underwent a sudden loss in immunoreactivity. This critical temperature was found to be pH dependent. The effects of polarity, pH, and temperature on epitope stability are consistent with changes in protein structural conformation. In addition, we found that certain fixatives cause a time and concentration dependent loss of epitope immunoreactivity. This study provides a rapid and easy determination of monoclonal antibody-defined epitope stability; the results of which serve to guide further studies on the antigen and to characterize the antigen on the basis of its unique physiochemical stability.

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

The BLA cross-idiotype (XId) is present on a unique subset of rheumatoid factors (RF) that cross-react with DNA-histone. In this study, prototype Bla monoclonal RF was shown from serologic investigations and N-terminal amino acid sequence analysis to have distinct kappa chains related to the V kappa III subgroup and VH4 heavy chains. The amino terminus of the heavy chain was cyclized, rendering the protein resistant to Edman degradation and providing a possible investigator bias to the published Ig sequence data to date. This appears to be the first definitive report of a serum IgM that expresses the VH4 gene. RF with DNA cross-reactivity have been reported to be produced by human and mouse cloned cells that have the VH4 or homologous mouse Vh36-60 gene.

A highly conserved conformational idiotope on human IgM rheumatoid factor paraproteins of the Wa cross-reactive idiotype family defined by a monoclonal antibody

Human IgM rheumatoid factors have been classified into major (Wa) and minor (Po) idiotypically cross-reactive families on the basis of reactivity with polyclonal anti-idiotypic antisera. Extensive structural studies have revealed that RFs from the Wa CRI family have homologous light chains. The structural basis of this CRI however is not known. In this study we have defined a conformational idiotope requiring the association of the VH and VL of a number of RF from the Wa CRI family for its expression and which thus comprise part of the Wa CRI. A murine monoclonal antibody, G8 specific for the idiotope reacted with 67% of RFs from the Wa CRI family. G8 also reacted with one IgG2K paraprotein with unknown specificity suggesting that the idiotope per se does not confer RF reactivity. Comparative studies of G8 expression relative to previously described sequence-dependent heavy and light chain associated idiotopes suggest that G8 recognises a separate determinant. Furthermore, the G8 idiotope is found on RFs expressing the VHI subgroup of heavy chain. Study of G8 expression in polyclonal IgM in normal sera demonstrated that the idiotope is widely expressed in the population. However, significantly higher levels of IgM bearing G8 were detected in the sera of patients with rheumatoid arthritis.

Expression of the major rheumatoid factor cross-reactive idiotype in juvenile rheumatoid arthritis

The major rheumatoid factor cross-reactive idiotype (RF-CRI), defined by prototypic monoclonal IgM rheumatoid factors, is expressed in high frequency by pokeweed mitogen-derived plasma cells from patients with rheumatoid arthritis who express RF in their sera. Unlike adults with rheumatoid arthritis, most patients with juvenile rheumatoid arthritis are seronegative for RF, as detected by classic IgG binding assays. We report that approximately 50% of seronegative patients with juvenile rheumatoid arthritis express the RF-CRI in high frequency among their pokeweed mitogen-derived plasma cells, and that approximately 33% of patients express the RF-CRI in high titer in their sera. The possible mechanisms for expression of an idiotypic marker of RF without expression of IgG binding activity by classic assays are discussed.

The major rheumatoid factor cross-reactive idiotype in rheumatic disease

The major rheumatoid factor cross-reactive idiotype (RCRI), a tertiary structure formed by both light and heavy chains, is found on 60% of all monoclonal IgM kappa RFs. To determine if the RCRI is expressed in patients with rheumatic disease, we used polyclonal rabbit anti-idiotypic antibodies to detect RCRI in sera and in pokeweed mitogen cultures of blood mononuclear cells (PBM) from patients with rheumatoid arthritis (RA) and juvenile rheumatoid arthritis (JRA). We detected increased expression of RCRI+, plasma cells in PWM cultures, and in sera from these patients. We have determined that some 7S IgM molecules from RF+RA patients are RCRI+, and can bind IgG in a sensitive RF ELISA. We have also observed that the CD5+ B cell subset, which is responsible for autoantibody production, generates RCRI+ antibodies. We review these data and discuss the relationship of the idiotypic network of interacting antibodies with rheumatic disease.

A Subgroup of Rheumatoid Arthritis (RA) Associated with Selective Binding of Rheumatoid Factors to Antigen Structures of Cytomegalovirus (CMV)

We compared antibodies (Ab) with both, antiviral and anti IgG properties in patients with rheumatoid arthritis with malignant progress, short remissions and no improvement to therapy. The selective binding of Rheumatoid Factor (RF) to antigen structures of CMV were tested in 180 patients by a newly established ELISA with antiidiotypic goat antibodies of CMV neutralizing human monoclonal Ab and against the virus antigen directly. Displacement reactions on the idiotypic bindingsite as well as comparative ELISA gave proof of the special RF activity. 24,2% of the patients suffering from RA, with IgM RF, showed selective binding to antigen structures of CMV and anti IgG activity.

The evidence of the specific binding capacity of RF to the virus antigen in chronic CMV infection as well as their defined binding capacity to the Fc Fragment of IgG suggest CMV specific RF as the pathogenetic factor of malignant forms of inflammatory rheumatism.

Idiotypic and subgroup analysis of human monoclonal rheumatoid factors. Implications for structural and genetic basis of autoantibodies in humans

Rheumatoid factors (RFs) in humans have been studied intensively because of their association with autoimmune and lymphoproliferative diseases. Many human IgM-RFs express cross-reactive idiotypes (CRIs) and have homologous light chains, some of which are encoded by a single V kappa gene, termed V kappa 325. However, although antibody activity generally requires the interaction between heavy and light chain variable regions, much less is known about structural relationships among RF heavy chains. To delineate further the structural and genetic basis of RF autoantibody synthesis, we generated "sequence-dependent" reagents specific for the human heavy and kappa light chain subgroups, and used them to analyze a panel of 27 monoclonal RFs. In addition, these proteins were tested for the expression of a heavy chain-associated CRI (G6), and a light chain-associated CRI (17.109). The results showed that most 17.109-reactive RFs contain heavy chains of the VHI subgroup, which bear the G6 idiotypic marker. However, among the 14 17.109-reactive RFs, two have heavy chains of the VHII subgroup, and another two contain heavy chains of the VHIII subgroup. Previously, we have shown that 17.109 is a phenotypic marker of the human V kappa 325 gene. Accordingly, these results demonstrate that the same human V kappa gene can combine with several VH genes from different VH gene subgroups to generate RF activity.

Human immune response to allergens of house dust mite, Dermatophagoides pteronyssinus. V. Auto-anti-idiotypic antibody characterization and cross-reactivity

From the serum of 10 allergic subjects we have prepared IgG antibodies recognizing idiotopes carried by specific antibodies to Dermatophagoides pteronyssinus (Dpt) allergens, and studied cross-reactivity of anti-Dpt IgG bystander and antigen-binding site-associated idiotopes by latex agglutination assays. Idiotopes of specific anti-Dpt IgE were evaluated by radioimmunoassays. Depending on the assay, a binding or inhibition of more than 50%, as compared to the reactivity of specific antibodies with the corresponding anti-idiotypic (anti-Id) IgG, was considered significant. Cross-reactivity of antigen-binding site-associated idiotopes attained a mean proportion of 6/10 for IgG and 9.6/10 for IgE. By contrast, bystander idiotopes cross-reacted only occasionally with a mean proportion of 2/10 for both IgG and IgE antibodies. Anti-Id antibodies from two subjects have been isolated by adsorption on insolubilized anti-Dpt antibodies of the corresponding patient. Using this purified material we have confirmed that (a) the majority of anti-Id antibodies carry an "internal image" of the initial antigen and compete in a dose-dependent manner with Dpt allergens for the binding to the anti-Dpt antibodies and (b) paratope-associated idiotopes of anti-Dpt antibodies are shared by unrelated individuals.

Complete protein sequences of the variable regions of the cloned heavy and light chains of a human anti-cytomegalovirus antibody reveal a striking similarity to human monoclonal rheumatoid factors of the Wa idiotypic family

The complete amino acid and nucleotide sequences of the variable regions of the heavy and light polypeptide chains of a human neutralizing IgGl anti-cytomegalovirus (CMV) antibody reveal a striking homology to IgM rheumatoid factors (RFs) of the Wa idiotypic family. The anti-CMV antibody and Wa RFs have in common VKIIIb, JKl, and VHIa gene segments but use different DH and JH gene segments. The anti-CMV antibody does not have RF activity and does not express the Wa idiotype. The Wa RFs do not have anti-CMV activity. A subset of Wa RFs, however, and the anti-CMV antibody do share several idiotypes on the VHIa and VKIIIb polypeptides. Since there are major differences in the antigen binding characteristics and some of the other expressed idiotypes, these data suggest that the D and J region amino acids are crucial to such specificities. Although the use of such highly homologous gene segments in different immune responses is well-documented in murine systems, these data represent the first such example in the human.

Cellular expression of rheumatoid factor cross-reactive idiotype in patients with seropositive and seronegative rheumatoid arthritis

A study has been made of the presence of the major rheumatoid Factor cross-reacting idiotype (RCRI) in the serum of patients with seropositive and seronegative rheumatoid arthritis as well as in the cytoplasm of plasmacells induced by cultivation of peripheral blood leucocytes (PBL) from the same RA patients and from normal humans. The PBL were stimulated in vitro with two different B cell mitogens, namely pokeweed mitogen (PWM) or Staph Auerus Cowan strain I (SAC). The RCRI was detected in the serum of seropositive RA patients and in the serum of four out of twenty seronegative RA patients. In these four, however, the seronegative condition was only apparent, since all four had hidden rheumatoid factors that could be shown after dissociation from IgG. The expression of the RCRI in the cytoplasm of PWM-stimulated PBL from seronegative RA patients was concordant with the expression in the serum. Thus the majority of truly seronegative RA patients also appear not to express the RCRI neither in the serum nor in the cytoplasm of plasmacells induced by PWM stimulation of PBL. An unexpected finding was the detection of the RCRI in plasmacells obtained by SAC stimulation of PBL from normal individuals. Up to 40% of RCRI-positive plasmacells were seen in many of these cultures, as opposed to an average of 2% in cultures stimulated with PWM from PBL of the same individuals. High percentages of RCRI-positive plasma-cells have previously been detected by us in PWM cultures only if these were from PBL from RA patients. Our working hypothesis is that PWM is a non-selective stimulator of B cells and that RCRI + precursors are in high frequency in RA patients, whereas SAC selectively stimulates these precursors even in normal PBL populations, where their frequency is not abnormally high.

A new protocol to digest human IgM with papain that results in homogeneous Fab preparations that can be routinely crystallized

A method has been developed for the routine production of Fab fragments from human IgM in high yield. After the IgM is purified at physiological pH, it is digested with papain in the presence of cysteine at room temperature for 16 hours. The Fab fragments are purified initially by gel filtration and then by ion exchange chromatography. The yield of Fab has been 60-80%. Some heterogeneity in the size of the Fabs from the different monoclonal IgMs has been observed. Fab fragments from four different IgM rheumatoid factors (RF) have been crystallized after such digestion and purification, in a variety of conditions including phosphate buffer alone or with the precipitating agents ammonium sulfate, polyethylene glycol or methylpentanediol. This modified papain digestion method has also been used for another non-RF monoclonal human IgM with equally good yield. Biological activity can be detected in the purified Fab fragment indicating that this procedure does not destroy the native conformation of the molecule.

Complete amino acid sequences of variable regions of two human IgM rheumatoid factors, BOR and KAS of the Wa idiotypic family, reveal restricted use of heavy and light chain variable and joining region gene segments

Evidence derived from the complete amino acid sequences of the variable regions of both the heavy and light chains of two members (BOR and KAS) of the Wa idiotypic family of human rheumatoid factors suggests that not only are the light chains of these molecules derived from possibly one variable region gene segment, but the heavy chain variable regions are all derived from the VHI subgroup of human V region genes. These molecules exhibit a surprising conservation in the size of D region, and all use the JH4 gene element. This restriction in use of VL, VH, D, and JH suggests all of these elements may play a crucial role in either antigen binding and/or expression of the crossreactive idiotype.

Human rheumatoid factor crossidiotypes. II. Primary structure-dependent crossreactive idiotype, PSL2-CRI, present on Wa monoclonal rheumatoid factors is present on Bla and other IgM kappa monoclonal autoantibodies

The amino acid sequence of the L-CDR2 (complementarity-determining region) of Bla mRF (monoclonal rheumatoid factor) is identical to that of the Wa mRFs. The PSL2-CRI (crossreactive idiotype), as determined by anti-PSL2, which has been shown to be present on all Wa mRFs, is also present on the Bla mRF and other monoclonal autoantibodies. PSL2-CRI is, therefore, not unique to Wa mRFs and may be present on most IgM kappa monoclonal autoantibodies. Whether PSL2-CRI is a crossidiotype (XId) that is selectively present on autoantibodies or represents an allotypic marker for a V kappa III gene is undetermined.