High Frequency of Monoclonal Immunoglobulins Exhibiting Natural Autoantibody-Like Activity in Patients with Multiple Myeloma and Waldenström Macroglobulinemia

Abstract 2893

Serum monoclonal immunoglobulins (M-Igs) of patients with monoclonal gammopathies are known to possess antibody activity against autoantigens, bacterial antigens and haptens, but their incidence is controversial. So far, high incidence of autoantibodies (autoAb) have been demonstrated against actin, Ro/SS-A and La/SS-B for M-Igs of all three classes (IgG, IgA, IgM) and against Fc fragment of IgG and the Ii group exclusively for IgM M-Ig. Other less frequent antiboby specificities of M-Igs include anti-myosin, anti-tubulin, anti-thyroglobulin and anti-DNA. M-Igs with anti-actin activity were found to express polyreactivity, which is a property of natural autoAbs (NAbs). NAbs are germ-line encoded, occur in all species, circulate in low concentrations and belong to all Ig classes. NAbs play important immunoregulatory role and anti-F(ab')₂ reactivity is crucial for the establishment of the idiotypic network.

The aim of this study was to investigate the frequency of human M-Igs that exhibit NAb-like activity in patients with monoclonal gammopathies and to explore possible correlations with their clinical features. Thus, 151 M-Igs (124 of IgG class: 71IgG-kappa/53 IgG-lambda and 27 of IgA class: 16 IgA-kappa/11 IgA-lambda) from patients with symptomatic multiple myeloma (MM; n=136), asymptomatic MM (n=8) or MGUS (n=7) and 50 M-Igs from patients with Waldenström Macroglobulinemia (WM) or IgM-MGUS (43 IgM-kappa and 7 IgM-lambda), without any autoimmune diseases, were studied by an in-house ELISA for polyreactivity against six autoantigens (native DNA, actin, tubulin, myosin, carbonic anhydrase, thyroglobulin) and the non-self hapten TriNitroPhenyl (TNP). Sera were also tested for antibody activity against F(ab')₂ fragment of human polyclonal IgGs. Most of these antigens are known targets of NAbs. Sera were first screened with enzyme-coupled human heavy chain antibodies (anti-G, anti-M and anti-A), and reactivity–with the exception of anti-F(ab')₂–was further attributed to the M-Ig using enzyme-coupled light chain antibodies (anti-kappa and anti-lambda).

A significant proportion (18.2%: 35/192 evaluated patients) of pathological sera exhibited anti-F(ab')₂ activity (27 from IgG-MM, 3 from IgA-MM and 5 from WM patients). Among the total M-Igs tested, 9.5% (18/189) recognised actin, 8.7% (17/194) carbonic anhydrase, 4.6% (9/194) thyroglobulin, 3.7% (7/186) TNP, 3.5% (7/196) tubulin, 2.5% (5/193) myosin and 1.5% (3/188) DNA. M-Igs reacting with actin, carbonic anhydrase, tubulin, myosin and TNP were found to belong to all three Ig classes (IgG, IgA, and IgM). Among the IgG M-Igs tested, the most frequent reactivity was that for thyroglobulin (7.6%), while among the IgA and IgM M-Igs the highest incidence observed was for actin and carbonic anhydrase (23%, 23% and 16.6%, 15.2%, respectively). Positive IgM and IgG M-Ig had either kappa or lambda light chain in a similar proportion, while positive IgA were mostly IgA-lambda (16/18). A high percentage of positive M-Igs from MM and WM patients were polyreactive (46%), i.e., reacted with at least two panel antigens. Polyreactivity was a prominent characteristic of IgA (6/6) and IgM (9/13) but not of IgG (6/36) M-Ig. Most frequent polyreactivity profile was that for actin, carbonic anhydrase and TNP.

There was no significant correlation of immune-related features of symptomatic WM (immune cytopenias, cold agglutinin disease, cryoglobulinemia) or of MM characteristics (ISS, CRAB, LDH, plasma cell infiltration) with any of the detected M-Ig specificities or their NAb-like profile.

In conclusion, we report for the first time anti-carbonic anhydrase and anti-TNP activity of the M-Igs from patients with monoclonal gammopathies. We also report high incidence of anti- F(ab')₂ activity in the sera of these patients as well as of polyreactive M-Igs. Our findings suggest that the M-Igs with NAb activity might reflect the expansion of a clone normally producing a NAb. To-date, it has been assumed that a naive B-cell is first driven to clonal expansion by antigenic stimulation and that subsequently, an oncogenic stimulus results in malignant transformation. Assuming that certain malignant monoclonal gammopathies arise from the proliferation of a clone normally producing a NAb which recognise F(ab')₂ and hence is probably involved in the regulation of the NAbs network, it may also be postulated that this may result in deregulation of this network.