A possible role for antibodies against spectrin in the interaction between erythroblasts and macrophages in vitro

The nature of serum factors which participate in the interaction in vitro between dimethylsulphoxide-induced Friend leukaemia erythroblasts (IFLE) and syngeneic mouse peritoneal macrophages was investigated. When heat-inactivated newborn calf serum (HI-NBCS) was depleted of IgG its activity to promote the association of neuraminidase-treated 59Fe-labelled IFLE (59Fe-IFLE) with macrophages was markedly reduced but could be restored by the addition of bovine IgG. Trypsin treatment of macrophages caused incomplete inhibition of their subsequent association with both untreated and neuraminidase-treated 59Fe-IFLE in the presence of HI-NBCS. When spectrin, the major red cell cytoskeleton protein, was added to HI-NBCS there was a dose-related inhibition of the association with macrophages of both untreated and neuraminidase-treated 59Fe-IFLE. Moreover a mouse monoclonal antibody against spectrin promoted the interaction of neuraminidase-treated 59Fe-IFLE with macrophages. Mouse sera which supported the association of neuraminidase-treated 59Fe-IFLE with macrophages were found to contain anti-spectrin antibodies. These results suggest that IgG antibodies mediate the interaction between erythroblasts and macrophages via trypsin-sensitive and trypsin-resistant receptors on the macrophage surface and that at least some of the antibodies show specificity for spectrin.