Selective activation of VH3A10+ rheumatoid factor producing B cells by staphylococcal enterotoxin D

Recognition of auto- and exoantigens by V4-34 gene encoded antibodies

The antigenic specificities of 24 V4-34-encoded monoclonal antibodies were compared with the amino acid sequence. The specificities were divided into three categories, red blood cells, B lymphocytes and auto/exoantigens. Six anti-I monoclonal antibodies, with multiple substitutions in their VH region, did not bind B lymphocytes or auto/exoantigens. Reactivity to these two antigens segregated with the 16 anti-i monoclonal antibodies, which were derived from the near germline V4-34 gene. All anti-i monoclonal antibodies bound B lymphocytes, albeit with varying intensities. B-cell binding correlated with basic amino acids in the VH-CDR3. Reactivity to auto/exoantigens was demonstrated only by a subset anti-i monoclonal antibodies and did not correlate with B-lymphocyte or i-antigen binding. These anti-ssDNA reactive monoclonal antibodies had basic amino acids in the VH-CDR3, strongly supporting the suggested role of arginine in DNA binding. However, an arginine-rich CDR3 was not enough to ensure DNA reactivity, since six other anti-i monoclonal antibodies that fulfilled this criteria did not bind ssDNA. Thus it is possible that the anti-DNA reactivity of V4-34-encoded monoclonal antibodies is mediated by the classic antigen-binding groove generated by the CDRs of the heavy/light chains. In contrast, anti-B-cell/i-antigen reactivity is mediated, unconventionally, by the V4-34 protein with a dominant influence of the VH-CDR3.

Pathogenesis of rheumatoid arthritis

Chronicity and destructive potential are characteristic features of the inflammatory response in the synovial membrane typical for RA. The dominant paradigm has proposed that an exogenous antigen, likely an infectious organism, targets the synovia and elicits a chronic immune response. Support for this disease model has come from describing the cellular components of the inflammatory lesions, which are composed of macrophages, T cells, and B cells. The observation that HLA molecules function by specifically binding antigenic peptides and presenting them to T cells has boosted the concept of an antigen-driven response. The last decade in RA research has been dominated by a shift from premolecular to molecular techniques. A major effort has been made to determine which cytokines and inflammatory mediators are produced at the site of disease. Tissue residing and infiltrating cells secrete proinflammatory cytokines in situ, which likely have a critical role in amplifying and maintaining the inflammation. We are beginning to understand that migration of inflammatory cells into the tissue is an important component of disease, specifically because adhesion molecules not only facilitate tissue infiltration, but also affect cell activation and cell-cell and cell-matrix interactions. The paradigm that RA is an antigen-driven and thus T cell-mediated disease has brought attempts to use T cell-depleting reagents as therapeutics. Although T cells could be eliminated in the peripheral blood, overall therapeutic benefits have been minimal and accompanied by major side effects. The lack of therapeutic efficacy has been demonstrated to be combined with the persistence and the selective proliferation of T cells in the joint, reemphasizing the role of tissue-infiltrating T cells in the disease. Studies of the composition of the T cell infiltrate have demonstrated heterogeneity, indicating that disease-relevant T cells are probably low in frequency. A new perspective on the role of T cells in RA has been opened by studies establishing that RA patients select a unique repertoire of T cells in the thymus and that clonal expansion of CD4 T cells is a frequent event in RA patients. Pathology of T cell function might be much more systemic than suspected so far. RFs remain the major autoantibodies in RA patients. In the last 10 years, it has become clear that they are not exclusively built under pathologic conditions but that RF-expressing B cells are an important element of normal immune responses. All immunoglobulin isotypes are represented among RF molecules. Some of them have accumulated somatic mutations, suggesting the influence of antigen recognition and T cell help. T cell control of RF production may explain the observation that RF positivity is an HLA-dependent phenomenon. Major progress in understanding pathologic events leading to RA can be expected by abandoning single hit models, which are too simplified and underestimate the complexity of the disease. In particular, taking into account that nonimmune tissues and mechanisms might be equally important in pathogenesis will open new avenues of conceptual approaches. Cross-fertilization will likely come from genetic studies aimed at detecting underlying genetic risk factors in common genetic disease. Emerging data indicate that several genetic risk determinants, each of which is nonpathologic if occurring alone, can add up to confer disease risk. One of these genetic elements in RA has been mapped to the HLA region. A sequence polymorphism in the HLA-DR B1 gene appears to be a strong genetic risk factor in several ethnic groups. Correlation of clinical presentation of RA and the inheritance of the RA risk gene suggests that the gene product is not necessary in disease initiation but functions by modulating disease pattern and severity. The next decade in RA research will be dedicated toward unraveling how genetic determinants can introduce pathology (e.g., how HLA genes can function as progre

Increased responsiveness of rheumatoid factor-producing B cells in seronegative and seropositive rheumatoid arthritis

OBJECTIVE

To compare the frequencies and responsiveness of rheumatoid factor (RF)-producing B cells in the peripheral blood of patients with seronegative and seropositive rheumatoid arthritis (RA).

METHODS

Frequencies of IgM+, IgG+, and RF+ B cells were determined by limiting-dilution analysis of purified peripheral blood B cells from 6 patients with seropositive RA, 8 patients with seronegative RA, and 7 normal controls. B cell help was provided by cloned T helper cells, which were stimulated by either anti-CD3 or the bacterial superantigen staphylococcal enterotoxin D (SED). IgM and IgG antibodies and RF in culture supernatants were detected by enzyme-linked immunosorbent assay.

RESULTS

In the presence of anti-CD3-stimulated T helper cells, 2-10% of B cells from normal individuals secreted IgM and IgG antibodies. The frequency of RF+ B cells was low and ranged from 1:182 to 1:885 (RF+: IgM+) B cells. In patients with seropositive RA, the numbers of Ig-producing B cells were reduced by a factor of 2, while the fraction of RF+ B cell precursors was expanded by more than 50-fold (7-20% of IgM+ B cells; P = 0.004). Patients with seronegative RA had higher frequencies of RF-producing B cells (1.5-6% of IgM+ B cells) than normal individuals (P = 0.002), but not to the same extent as seropositive patients (P = 0.002). Stimulation of B cells using SED preferentially induced RF+ B cells in normal controls and in patients with seronegative and seropositive RA.

CONCLUSION

B cell precursors with the potential to secrete RF were detectable in high frequencies in normal individuals and in patients with seropositive and seronegative RA. In all donors, these B cells could be stimulated with the bacterial superantigen SED. In normal individuals, RF+ B cells remained nonresponsive to help provided by anti-CD3-activated T cells, but were responsive in RA patients. Seronegative and seropositive RA form a continuous spectrum of disease, with a higher number of RF-secreting B cells in the seropositive patients.

B-cell superantigens: implications for selection of the human antibody repertoire

For several decades, B-cell interactions with antigens were thought to occur only through a clonal activation mechanism, in which the hypervariable regions of the immunoglobulin receptor are exclusively involved in ligand binding. However, an additional mode of interaction can occur, whereby molecules, termed B-cell superantigens, can bind human B cells bearing immunoglobulin receptors of a given variable (V)-gene family. This mechanism requires contributions from regions outside the conventional hypervariable loops and results in a B-cell response of increased magnitude. Here, Moncef Zouali reviews recent in vitro and in vivo observations on human B-cell superantigens in the context of the current consensus of B-cell development, and discusses the implications of these novel concepts with respect to pathogenesis.