Helper activity for antibody synthesis encoded by mRNA extracted from human peripheral blood mononuclear cells

Translation products in Xenopus laevis of mRNA from human peripheral blood mononuclear cells were tested for their capacity to replace T cells in the anti-SRBC response of nude spleen cells. When the starting material came from PHA or FCS-stimulated lymphocytes, the translated lymphokines, displaying such a B cell helper activity were found to be encoded by mRNA sedimenting at 6-7S and 13S on a sucrose density gradient. 6-7S mRNA from control, non-stimulated lymphocytes was also able to code for B cell helper activity. Thorough T-cell depletion of mouse responder cell populations left unchanged the activity of 6-7S mRNA products while preventing that of 13S products. The latter were found to contain IL-2, which suggests that their action on B cells was indirect, mediated by T-cell stimulation.