Preliminary analysis of primary and secondary anti-Thy-1 responses elicited by immunization with cell-bound and cell-free antigen.

Primary and secondary anti-Thy-1 responses were elicited in C57BL/6Kh and (C57BL/6Kh X BALB/cKh)F1 mice by injection of either intact or sonicated Thy-1 disparate thymocytes as the source of the two forms of Thy-1 antigen--cell bound and cell free, respectively. The primary response was characterized by a high number of anti-Thy-1 plaque-forming cells in the spleen and a high titer of serum antibodies that belonged predominantly to the IgM class. The secondary response consisted of a moderate number of plaque-forming cells and a high titer of serum antibodies that belonged to the IgG and IgM classes. Only secondary responses ensued in mice primed and boosted with the same form of antigen, whereas primary and secondary responses developed concomitantly in animals primed with one form and boosted with both forms simultaneously. These data suggested that the two forms of Thy-1 antigen activate in a given responder two discrete subsets of T cells.