Antibody synthesis by chicken spleen cells in vitro. I. Requirements of B cells at various stages after immunization for T cells, macrophages and antigen.

Abstract

AbstractThe requirements for T cells, macrophages and antigen during the induction of in vitro antibody responses were ascertained with chicken spleen cells obtained at various times after immunization with sheep red blood cells (SRBC). The IgM plaque‐forming cell (PFC) response was T cell independent exclusively in cultures initiated 3 days after priming, but macrophage dependent at all time intervals tested. In cultures started 4 to 10 days after priming the IgG response was both T cell and macrophage independent and PFC numbers remained at a high plateau level throughout the culture period. In contrast, IgG responses initiated more than 15 days after priming showed a reversal to complete T cell and macrophage dependence and were characterized by a sharp increase in PFC numbers between days 2 and 4 of culture. Formaldehyde‐fixed SRBC were immunogenic for IgG PFC 4 to 10 days after priming but failed to stimulate later IgG memory and all IgM responses. Contrasting antigen dose requirements for IgM and IgG responses were found in cultures initiated at various periods after priming.The results suggest that direct contact with fixed antigen was sufficient to maintain IgG antibody synthesizing PFC in vitro, while native antigen and cell co‐operation were required for late secondary IgG and all IgM responses. These results are interpreted in terms of separate pathways of differentiation for IgM and IgG antibody‐producing cells. A distinct 3rd day stage of T cell‐independent but macrophage‐dependent responsiveness for both classes of antibody was also defined.