A standardized human T-lymphocyte proliferation assay for detecting soluble accessory factors from monocytes. I....

Monocyte (M phi-) depleted human peripheral blood mononuclear cells exhibit reduced capacity to proliferate, when stimulated with low doses of phytohaemagglutinin (PHA). Stimulation with higher doses of the mitogen or addition of graded numbers of autologous M phi's potentiated the response proportionally, and 10% M phi's restored the response completely. Addition of only 0.1% M phi's was needed for potentiating the response significantly. Pretreatment of M phi's with Actinomycin-D or heating impaired the accessory effect, whereas x-irradiation had no effect. The presence of M phi's did not influence the viability of the proliferating lymphocytes. Crude supernatants from M phi-cultures, even at very low concentrations, partly restored the PHA response, as did preparations of highly purified human Interleukin-1.