Selective induction of DNA synthesis in T and B lymphocytes

Abstract

The ability of concanavalin A (Con A) and a lipopolysaccharide from E. coli bacteria (LPS) to induce DNA synthesis in various types of mouse lymphocytes cultivated in vitro was investigated. The results demonstrate that Con A is selectively active on T cells, being capable of activating DNA synthesis in thymocytes, cortisone-treated thymocytes, peripheral “educated” T cells, spleen cells and to a smaller degree bone marrow cells. When T cells are removed from spleen cell suspensions by treating them with antitheta serum, the effect of Con A is markedly reduced. Spleen cells from thymectomized and lethally irradiated mice repopulated with antitheta serum treated bone marrow (T × B mice) or spleen cells from congenitally athymic (nude) mice do not respond to Con A. Cortisone-treated thymocytes and spleen cells responded equally well to Con A; whereas untreated thymocytes respond 10 to 20 times less, suggesting that the cortisone-resistant thymocytes are the responsive cells both in the thymus and in the spleen. Pure T cells exhibited a very narrow dose response profile to Con A, 5 μg being optimal and 1 or 10 μg giving a small, or no, response. Contrarywise, a mixed T and B cell population, such as the spleen, showed a broad dose response profile to Con A. It is suggested that Con A-activated T cells can influence B cells to respond to Con A; whereas B cells by themselves cannot be activated by Con A. LPS cannot activate thymocytes, cortisone-treated thymocytes, or educated peripheral T cells, but stimulates DNA synthesis to an equal degree in normal spleen cells, antitheta-treated spleen cells, spleen cells from T × B or nude mice and normal bone marrow cells. LPS can induce DNA synthesis in spleen cells from animals tolerant to LPS to the same degree as in normal spleen cells. Another thymus-independent antigen (PVP) cannot activate DNA synthesis in normal spleen cells, suggesting that LPS exerts a non-specific stimulatory effect on B cells.