Natural serum antibodies which bind to damaged erythroblasts: isotypes and light-chain composition

Dimethyl-sulphoxide-induced Friend leukaemia erythroblasts (IFLE) which had been damaged by treatment with inhibitors of protein synthesis (cycloheximide, puromycin) were incubated with normal mouse serum or with doubling dilutions of it. The erythroblasts were subsequently tested for their binding of natural antibodies of all the major immunoglobulin (Ig) isotypes and both light-chain types, using Fc- and light-chain-specific FITC-immunoconjugates, and flow cytometry. After short-term (4-h) exposure of IFLE to puromycin, some binding of IgG but not of IgM or IgA could be demonstrated. By contrast, prolonged (17-h) exposure of IFLE to cycloheximide or puromycin resulted in their reaction with antibodies of all major isotypes (IgM, IgG1, IgG2a, IgG2b, IgG3, IgA) containing kappa-light chains. Under these conditions of damage the percentage of IgM- or IgG-binding IFLE significantly exceeded that of IgA-reactive cells. Moreover, the percentage of damaged IFLE which bound IgG2a or IgG3 was greater than that of cells which bound IgG1 or IgG2b. The percentage of damaged IFLE which bound a certain Ig-isotype did not correlate with the concentration of that Ig-isotype in normal mouse serum. The results suggest that natural antibodies of all major isotypes containing kappa-light chains bind specifically to severely damaged IFLE and could facilitate their interaction with macrophages in a concerted manner.