THE GLYCOSYLATION OF RED-CELL AUTOANTIBODIES AFFECTS THEIR FUNCTIONAL-ACTIVITY IN-VITRO

Factors governing the functional activity of red cell autoantibodies a re poorly defined. Here we report the presence of qualitative differen ces in the glycosylation of IgG autoantibodies which affect in vitro i nteractions with Fc gamma RIII. The following antibodies were affinity -purified by adsorption and elution from normal red cells: IgG eluted from the red cells of 27 haemolysing or non-haemolysing patients, anti -D in sera from 11 pregnant women, and IgG1 and IgG3 human monoclonal anti-D, Monoclonal antibodies with differing levels of agalactosyl IgG were produced by culturing cell lines at high or low cell density, Th e % IgG with oligosaccharides lacking terminal galactose residues (aga lactosyl IgG) of antibodies was designated-as low, medium or high acco rding to their reactivity with a monoclonal antibody to terminal N-ace tylglucosamine. Fc gamma RIII-mediated functional activity was assesse d by measuring the K-cell-mediated lysis of red cells in eluates dilut ed to achieve comparable levels of red cell sensitization, AU eluates containing allo-anti-D were lytic (range 74-100%), In contrast, lysis by autoantibodies varied from 0 to 100%: 11/13 eluates from red cells of haemolysing patients promoted >5% lysis compared to 2/7 eluates fro m red cells of non-haemolysing patients (P<0.02). The ability of autoa ntibodies to promote K-cell-mediated red cell lysis correlated inverse ly with their level of agalactosyl IgG (r=-0.56, P<0.01, n=23). Furthe r, monoclonal anti-D antibodies with very low levels of agalactosyl Ig G were comparatively more lytic than the same antibodies containing mo re agalactosyl IgG, Analysis of the ratio of kappa:lambda light chains suggested that autoantibodies from 6/19 patients were monoclonal or o ligoclonal in nature, The data indicate that IgG red cell autoantibodi es from different patients are functionally heterogenous, and that thi s may be due, at least in part, to qualitative differences in the Fe r egion glycosylation reflected by differences in the proportion of agal actosyl IgG. This heterogeneity is consistent with the clonally-restri cted nature of the autoantibodies in some patients.