Red blood cell requirements of human T lymphocyte colonies.

T lymphocytes were induced to form colonies by stimulating mononuclear cells with phytohaemagglutinin (PHA) prior to seeding in agar. The resultant colonies showed heterogeneity in the number of cells per colony and their location of growth, be it within the agar or, less frequently, on top of the agar. Colonies were subdivided according to their size and site of growth. The enhancing effect of sheep red blood cells (SRBC) was investigated through single and double agar experiments. The results indicated that SRBC and red blood cells (RBC) from other sources supported T lymphocyte colony development through a factor or factor(s) that diffused through the agar rather than by direct contact between RBC and the proliferating lymphocytes.