T lymphocyte and monocyte-macrophage interaction in colony-stimulating activity elaboration in man.

Using in vitro culture systems. we have studied the effect of coincubating human monocyte-macrophages with autologous T lymphocytes on colony-stimulating activity (CSA) elaboration in response to methanol extraction residue (MER) of BCG. When monocyte-macrophages were coincubated with T lymphocytes for 4 days at a ratio of 1 :3. the resultant colony-stimulating activity. assayed against light density nonadherent human marrow cells. was significantly higher (p < 0.01 ) than that derived from macrophages incubated alone at equivalent cell concentrations. The T lymphocytes did not elaborate any significant CSA in response to MER. On the other hand, when monocyte-macrophages were coincubated with concanavalin A and thymosin (fraction 5) primed T lymphocytes at a ratio of 1:3. the respective resultant CSA was only 51 % and 46%, respectively, of that obtained from monocyte-macrophages coincubated with nonprimed T lymphocytes. This suppression was noted for both neutrophil and eosinophil colonies. although it was more marked for the latter. These data suggest that T lymphocytes may augment as well as suppress the CSA elaboration when incubated with monocyte-macrophages. This T-lymphocyte modulation of CSA elaboration may depend on the degree of prior activation of helper and suppressor T lymphocytes.