Abstract
A soluble factor (TRF) produced by mixtures of allogeneic mouse spleen, lymph node, and thymus cells functionally replaces T cells in a primary IgM antibody response to sheep blood cells in vitro. It is now shown that TRF can also reconstitute an IgG antibody response in T cell-deprived spleen cultures derived from preimmunized mice. The optimal time of addition and the amount of TRF required differ between primary and secondary in vitro systems.