Regulatory effects of macrophage-secreted factors on T-lymphocyte colony growth

Colonies of mouse T lymphocytes developed when lymph node cells, presensitized with PHA in liquid culture, were seeded in a two-layer soft agar culture system containing the mitogen in the lower layer. The clonal proliferation was suppressed when culture fluid supernatants from macrophages (adherent peritoneal cells or spleen cells) from a number of mouse strains were incorporated in the agar culture system. The magnitude of the suppression was a function of the number of cells used to prepare the culture fluid and the amount of supernatant added to the culture. The inhibitory effect disappeared with dialysis and the dialyzed culture fluid exhibited an enhancing effect on T-lymphocyte colony proliferation. Diaflo ultrafiltration of culture fluid supernatant separated two substances, lymphocyte colony-inhibitory factor (LCIF), concentrated mainly in the fraction with molecular weight of less than 1000, and lymphocyte colony-enhancing factor (LCEF), located chiefly in the fraction with molecular weight of 10,000 to 30,000. The inhibitory factor was heat stable, while the enhancing factor was heat sensitive. LCIF was not species specific. It appears that adherent cells-marcophages release two biologic substances able to influence the cloning of T lymphocytes, lymphocyte colony-inhibitory factor and lymphocyte colony-enhancement factor. Unless the two are separated, the mild activity of LCEF is completely masked by the relatively strong action of LCIF.