Reaction of human anti-antibodies with incomplete anti-D and its sub-units

Characterization and V(H) sequences of human monoclonal anti-F(ab')(2) autoantibodies from normals and Sjögren's syndrome patients

To investigate the genetic background of anti-F(ab')(2) autoantibodies and the mechanism behind their production we have analyzed 10 human monoclonal antibodies directed against IgG F(ab')(2) and IgG Fab. They were all derived from peripheral blood by the EBV/hybridoma technique. Eight were from three healthy individuals and two from two patients with primary Sjögren's syndrome (pSS). They react with epitopes on distinct regions of IgG, including epitopes present on or near the hinge of IgG, epitopes on the Fd gamma, and an antigenic determinant(s) present on lambda light chains. These determinants are either exposed on the intact IgG molecule or revealed following pepsin or papain digestion. The V(H) germline gene repertoire used is diverse and with considerable overlap with that used by rheumatoid factors (RF). The two IgG antibodies from normals are extensively mutated (13 and 24 mutations/V(H)), but with a replacement to silent mutation ratio in the CDR(H)1 + 2 of only 3.7. The IgM antibodies from normals are also heavily mutated (mean 10 mutations/V(H)). This suggests that anti-F(ab')(2) from normals are generated by an antigen-driven somatic hypermutation mechanism. In contrast, the two IgM antibodies from pSS are virtually unmutated in both V(H) and V(L). Together with published data of pSS RF and anti-Ro 52-kDa sequences (1-3), this suggests that there is an expanded population of naïve B cells with autoantibody specificities in the peripheral blood of pSS patients.

Studies of human anti-gamma-globulin factors reacting with pepsin-digested gamma-globulins

Many sera from normal individuals as well as patients with various disease states contain agglutinating antibodies which show specificity for antigenic determinants of gamma-globulin revealed by pepsin digestion at pH 4.1. Sera containing such agglutinating activity as well as sera negative for these agglutinators contain low molecular weight (3S-5S) components of slow gamma-mobility which inhibit these agglutination reactions. Low molecular weight inhibitors show both auto- and isospecificity, and are antigenically related to the 5S pepsin fragment of gamma-globulin. A common situation is thereby revealed in which human anti-gamma-globulin antibodies showing specificity for pepsin-digested gamma-globulins are present in serum along with low molecular weight gamma-globulin components capable of inhibition. Autoreactivity or autospecificity of such anti-gamma-globulin factors is a phenomenon shared by both normal human sera and sera from patients with various disease states.