Effect of low molecular weight human serum factors and human somatomedin peptides on human lymphocyte cultures.

Using PH]thymidine incorporation into DNA of human lymphocytes in culture, we have shown that human serum contains an ultrafiltrable factor(s) that sensitizes the activation of lymphocytes by phytohaemagglutinin. This (these) factor(s) can replace either human serum or foetal calf serum in the culture. In addition, it permits the expression, and therefore the assay, of human somatomedin A peptides. In somatomedin assays we have shown that the assay using lymphocytes is a much more sensitive test than the assay using sulphation of chick embryo cartilage.