Characterization of mouse cells releasing or responding to mitogenic factor induced by phytomitogens in vitro

Mouse lymphocyte populations exposed to mitogen were tested for their capacity to release factors that stimulate other lymphocytes to synthesize DNA or enhance their response to mitogens in vitro. The target lymphocyte for this mitogenic factor(s) (MF) was also characterized. The results showed that lymph node and spleen cells release more MF than thymocytes upon exposure to Con A, PHA or PWM in vitro. The T cells were found to be largely responsible for MF production, since cell suspensions depleted of phagocytic cells did not exhibit any decreased ability to produce MF and spleen cells from congenitally athymic (nude) mice produced no detectable MF activity. The MF stimulated thymocytes, lymph node cells, and spleen cells to synthesize DNA. Spleen cells from nude mice were also stimulated. The MF released by lymphocytes in response to Con A was found to induce DNA synthesis of lymphocytes in itself and did not require the presence of mitogen. It is concluded that phytomitogen lectins stimulate T cells to synthesize DNA and to release soluble factor(s) which are mitogenic for both T and B cells. The latter cells may thus be unresponsive to the phytomitogen, but still undergo blast transformation.