Splenic dependence of the antibody response to thymus-independent (TI-2) antigens.

The murine antibody response to T-independent (TI)-2 antigens [2,4-dinitrophenyl-Lys-Ficoll (DNP-FIC) and DNP-hydroxyethyl starch (HES)] was impaired long after splenectomy, while responses to TI-1 [trinitrophenylated lipopolysaccharide (TNP-LPS)] and thymus-dependent [TNP-keyhole limpet hemocyanin (KLH)] antigens were largely unaffected. The antibody response to these TI-2 antigens was exclusively against the conjugated epitopes [DNP-, fluorescein isothiocyanate (FITC)- or tetramethylrhodamine isothiocyanate (TRITC)-Ficoll or -HES]. Fluorescent conjugates of Ficoll and HES localize selectively to the splenic marginal zone macrophages. This localization was not affected by 750 cGy of X-irradiation, but the antibody response to the TI-2 antigens was abrogated for 14 days. Administration of spleen cells restored the antibody response to these TI-2 antigens in otherwise intact irradiated mice but not if they had been splenectomized. Our findings indicate that the antibody response to TI-2 antigens depends upon stimulation of B cells in a splenic environment. This probably involves antigen presentation by marginal zone macrophages.