Studies on the relationship between HLA DR4 and in vitro IgM rheumatoid factor production

Value of laboratory tests in early prediction of rheumatoid arthritis

OBJECTIVE

To determine which laboratory test or tests at presentation best predicted a diagnosis of rheumatoid arthritis (RA) 2 years later.

METHODS

Two hundred seventy patients with early arthritis seen in 7 hospitals underwent comprehensive evaluations at 6-month intervals for 2 years, when the diagnosis of RA was assessed by 5 rheumatologists. The sensitivity and specificity of each test at the first visit for discriminating between RA (38%, n = 98) and non-RA patients were determined. Optimal cutoffs for continuous tests were derived from receiver operating characteristic curves. Sensitivity and specificity of test combinations selected by multiple logistic regression were determined.

RESULTS

IgM rheumatoid factor (RF) by enzyme-linked immunosorbent assay, IgG-antikeratin antibody (AKA), and latex test had the strongest associations with RA. These 3 tests formed the most powerful combination for distinguishing RA from non-RA.

CONCLUSION

IgM-RF, IgG-AKA, and the latex test are the best laboratory tests for discriminating between patients with and without RA. Combining these tests slightly improves diagnostic value.

The relationship between circulating CD5+ B lymphocytes and in vitro autoantibody synthesis in normal individuals

Recent observations suggest that a subpopulation of B lymphocytes bearing the phenotype CD5+ may be enriched for cells committed to the synthesis and secretion of autoantibodies. We had previously shown that a subset of normal individuals has an expanded subpopulation of B lymphocytes committed to the synthesis of IgM and IgM-rheumatoid factor (RF), and that this condition was associated with HLA-DR4 (4). In these studies, we performed simultaneous quantitation of the size of the circulating CD5+ B lymphocyte subpopulation in a group of 20 normal donors, and of the pokeweed mitogen-induced in vitro synthesis of a panel of autoantibodies by the same peripheral blood cells depleted of CD8+ suppressor lymphocytes in 18 of the 20 individuals. The culture supernatants were assayed for total IgM and IgG, RF, IgM, and IgG anti-single-stranded DNA, anti-human thyroglobulin, and anti-tetanus toxoid. The mean percentage CD5+ B cells was 13.5 +/- 2.5%. There was no significant correlation between total B lymphocytes and CD5+ B cells (R = 0.25, P greater than 0.20. Positive correlations were found between the proportion of circulating CD5+ B lymphocytes and synthesis of RF (R = 0.73, P less than 0.001), and IgM anti-DNA (R = 0.58, P less than 0.03). Significant correlations were not found between CD5+ B cells and secreted IgM or IgG antibodies against the exogenous antigen tetanus toxoid, measured in the same supernatants. The antibodies produced in vitro by T cell-dependent B cell activation appear to have limited or no polyspecificity. These results indicate that the size of the circulating CD5+ B cell subpopulation in any given individual contributes importantly to the magnitude of autoantibody synthesis in cultures where T cell-mediated B lymphocyte activation takes place in the absence of suppressor signals.

Occurrence of a rheumatoid factor cross-reactive kappa light-chain idiotope in rheumatoid arthritis families

The occurrence of IgM rheumatoid factor (RF) and RF-associated kappa-III light-chain idiotope identified by monoclonal antibody 6B6.6 in the serum from 22 patients with rheumatoid arthritis (RA) and 68 relatives without connective tissue diseases in 15 families was determined by solid-phase enzyme-linked immunosorbent assays. Serum IgM RF was present in 19 RA patients from 12 families and 12 arthritis-free relatives of 4 families. It was not found in any of 9 spouses included in the study or in 44 of 45 unrelated healthy adult controls. RF-associated 6B6.6 idiotope was detected in 42% of the IgM RF(+) RA patients and in 50% of the IgM RF(+) arthritis-free relative, but not in the adult controls, spouses, and IgM RF(-) RA patients and relatives. It was present in one RA serum from each of 8 families and 6 sera from arthritis-free relatives of 2 families (5 of whom were from one family). Where present, the idiotope-positive RF represented only a small fraction of the serum IgM RF of the RA patients (0.1-2.1%) and relatives (1.5-14%). The increased frequency of IgM RF(+) individuals, with and without RA, in family groups suggests a genetic predisposition for expression of RF. The small proportion of RF bearing the 6B6.6 idiotope in both RA patients and unaffected family members supports the view that the number of germline genes encoding for RF is large or that extensive mutation occurs in the course of RF expression, whether idiopathic or associated with RA. In addition, nonuniform expression of the idiotope in RF within family groups indicates that the various clones of RF producing cells are to a large extent independently regulated.

Rheumatoid arthritis

The results of family and twin studies suggest that RA may result from an interaction between an oligogenic susceptibility and unknown environmental factors. Part of this genetic predisposition is accounted for by genes within the MHC where there is a well-documented association with HLA-DR4. Studies of DR and other MHC variants have shown different associations with particular subgroups. One subgroup is Felty's syndrome where there is a strong association with DR4, as well as associations with DQ-beta and C4B null variants when DR4-matched Felty's and RA subjects are analysed. These DQ-beta and C4B null variants may characterize a single haplotype which is associated with extra-articular disease. A further rheumatoid subgroup characterized by circulating antibodies to native type II collagen, shows an association with HLA-DR3 and 7. Genes on chromosome 14 may also influence susceptibility to RA, probably by interaction with MHC genes and there are different Gm associations for DR4-positive and collagen-antibody-positive rheumatoid subgroups. HLA and Gm markers so far identified only account for a small part of the total genetic predisposition to RA and a third or further loci may also be involved. Possible candidates include T-cell alpha- and beta-chain genes and immunoglobulin light chain genes. One present concept of the genetic predisposition to RA is of several independent immunogenetic pathways each including interactions at two or more loci.

The incidence of rheumatoid arthritis is predicted by rheumatoid factor titer in a longitudinal population study

Rheumatoid factor (RF) is often detected in subjects who do not have rheumatoid arthritis (RA). To determine if the presence of RF is predictive of the development of RA, 2,712 Pima Indians of Arizona, 20 years of age or older, initially without RA, have been observed for up to 19 years with biennial examinations. These included a medical history, physical examination of the joints, radiographs, and RF determination by sheep cell agglutination test. During the study period, 70 new cases of RA developed. When the population at risk was stratified by RF titer, with reclassification at subsequent examinations if the RF titer changed, the age- and sex-adjusted incidence of RA increased with higher titers of RF. The incidence of RA (in cases per 1,000 person-years) according to RF titer was 2.4 (RF titer less than 1:2); 6.7 (titer 1:2-1:16); 11.0 (titer 1:32-1:256); and 48.3 (titer greater than 1:256) (P less than 0.001). The same trend was also found within each age and sex group, and within groups defined by the number of American Rheumatism Association criteria present before the definite diagnosis. We conclude that the presence of RF, in subjects without RA, is a risk factor for the development of RA, and that this risk is related to the RF titer. It is also suggested that RF may represent a marker of the earliest phases of the pathogenetic process of RA, that may be detectable before the appearance of other features that permit a clinical diagnosis.

Epidemiological and genetic aspects of IgM rheumatoid factors

The occurrence of IgM rheumatoid factors (RF) was studied in a random sample of 8807 persons aged between 20 and 50 years in Tromsø, North Norway. Seropositivity for IgM RF was defined as a Waaler titre of 40 or more. A total prevalence of IgM RF of 1.36% was found, and a prevalence between 0.48-0.94% was found among the healthy persons, with no sex difference. Approximately 50% of IgM Rf positives are thus healthy. Only 11% of those with IgM RF suffered from rheumatoid arthritis. The majority of RF positive sera from healthy persons were low titred, and 81% of them converted to seronegativity in the course of 3.5 years. A low titred IgM RF appears rather harmless, while a high titre indicates a specific disease process. No association between IgM RF and DR4 could be found in healthy persons. The frequencies of Gm-allotypes a, b, e, f-n and x in healthy, RF positive individuals did not differ from the RF positive patients with RA, suggesting that the Gm-allotypes are not involved in the genetic pre-disposition for RA.

High levels of in vitro IgM rheumatoid factor synthesis correlate with HLA-DR4 in normal individuals

The association between the HLA-DR4 histocompatibility antigen and in vitro synthesis of IgM and IgM rheumatoid factor (IgM-RF) by blood mononuclear cells was investigated in 35 normal subjects. In vitro cultures of T and B cells were stimulated with pokeweed mitogen, and the secreted IgM-RF, tetanus antibody, and total IgM protein were measured by solid-phase radioimmunoassay. In cultures containing unseparated T cells, IgM-RF production in the DR4+ and DR4- subgroups was not significantly different. However, depletion of OKT8+ cells containing T suppressor cells resulted in significantly higher IgM and IgM-RF synthesis in the DR4+ subgroup. Moreover, 6 of the 8 highest levels of IgM-RF were produced by DR4+ individuals, while only 7 of the remaining 27 individuals were DR4+ (P = 0.035). Ratios of secreted IgM-RF:IgM indicated that there was a relative enrichment for IgM-RF- specific B cell precursors in DR4+ high responders, although total numbers of circulating B cells were not increased. High responder B cells had high levels of responsiveness when mixed with T helper cells from low responders, whereas low responder B cells consistently produced low responses, even when cocultured with T helper cells from high responder donors. The data suggest that a subset of normal individuals has a pokeweed mitogen-responsive lymphocyte population that contains a B cell subpopulation specific for IgM-RF synthesis and that this condition is associated with HLA-DR4. In certain individuals who have the DR4 type, there may be a component of a susceptible genetic background, upon which other factors act to induce IgM-RF synthesis and which may produce clinical manifestations of rheumatoid arthritis.

Enhanced in vitro IgM rheumatoid factor synthesis in seropositive rheumatoid arthritis families

We studied the patterns of in vitro IgM RF production by peripheral blood mononuclear leukocytes (MNL) in first- and second-degree relatives and non-blood relatives of 14 RA patients. In all these included 25 individuals with RA (14 probands, 11 other affected members), 88 non-affected first- and second-degree relatives and 15 non-affected non-blood relatives. In vitro production of IgM RF and IgM by MNL from RA patients was similar to what we and others have previously described. Spontaneous production of IgM RF was demonstrated by MNL from some RA patients and the ratio of IgM RF to total IgM was higher for patients than controls. The non-blood relatives failed to demonstrate spontaneous in vitro IgM RF production. In contrast, MNL from approximately 16% of non-affected blood relatives spontaneously produced IgM RF. Spontaneous IgM RF production in this group did not correlate with HLA-DR3 or HLA-DR4 and was found in Caucasoids. American blacks, simplex (one affected individual), and multiplex (more than one affected individual) families. Linkage analysis using either a recessive or dominant model of inheritance failed to detect linkage among affected and non-affected family members.

Spontaneous and pokeweed mitogen induced production of rheumatoid factor and immunoglobulins in type II essential mixed cryoglobulinaemia

In order to evaluate functional lymphocyte defects in type II essential mixed cryoglobulinaemia (EMC) in vitro production of immunoglobulins (Ig) and rheumatoid factor (RF) has been studied in basal conditions and under pokeweed mitogen (PWM) stimulation in 15 patients and in 17 control subjects. The major finding was a significantly high basal and inducible production of RF by EMC lymphocytes as compared with the RF production in controls, while synthesis of polyclonal Ig was unaffected. A good correlation existed between in vitro production and serum levels of RF. Peripheral blood SmIg+ and Ia+ cells were also significantly increased. The possibility that EMC shares some pathogenetic mechanism with rheumatoid arthritis on the one hand and with lymphoproliferative diseases on the other is considered.

Rheumatic diseases in an Icelandic family. Clinical and immunological survey

We have studied 192 members of a highly inbred Icelandic family with clustering of rheumatic diseases. Twelve consanguineous marriages are known in the family and 54 of 65 surviving offsprings of these (inbred group) were traced. Thirty-nine family members were affected by rheumatic diseases; 18 of them belonged to the inbred group. Eleven of 20 family members with rheumatoid arthritis (RA) came from the same inbred group. Eleven of the inbred group had a positive Rose-Waaler test for rheumatoid factor (RF) and the inbred group had significantly higher serum levels of IgG and IgM than an age and sex matched group from the family. Serum IgM RF was significantly associated with the age of the family members, but IgA RF and IgG RF did not show any such association. The possible role of recessive genes in the rheumatic diseases, as well as the inbreeding effect regarding certain extended HLA-complotypes is discussed.

Rheumatoid arthritis: relationship with HLA-D

Understanding of the genetic component of rheumatoid arthritis has been greatly enhanced by the discovery of the association of risk for development of this disease with certain histocompatibility antigens. The HLA-D region, at the centromeric end of the HLA gene complex, on the short arm of chromosome number 6, is concerned with important functions in the regulation of the immune response. The products of the HLA-D region (DR, SB, MT, and the like) function as "restriction elements" for antigen presentation, mediators of immune response and immune suppressor genes, stimulators of graft rejection, and of other allogenic effects. Rheumatoid arthritis is associated with Dw4 and DR4 in Caucasians. The association with DR4 has been observed also in Blacks and Orientals. HLA-DR4 is associated with more severe, rheumatoid factor-positive disease. Clinical and genetic heterogeneity has been revealed by studies of patients with juvenile arthritis. Conditions often associated with rheumatoid arthritis and also thought to have an immunologic basis, such as Sjögren's syndrome, Felty's syndrome, and rheumatoid vasculitis, and reactions to medications, such as gold and penicillamine, reveal an interesting spectrum of immunogenetic relationships. Thus, HLA studies have shed light on the classification of patients with rheumatoid diseases. In view of the role of HLA-D in the immune response, these studies are expected to further our understanding of the mechanism underlying predisposition for development of rheumatoid arthritis and related conditions.