A microplate culture system has been standardized for blastic transformation of lymphocytes, using various mitogens more or less specific to T lymphocytes (concanavalin A, phytohaemagglutinin, erythrogenic toxin) or B lymphocytes (lipopolysaccharides and their lipids A, pokeweed mitogen). The mitogen-stimulated lymphocyte activation was examined by the use of the nucleolar test determining the state of nucleolar RNA synthesis by morphologic criteria. In this introductory paper to a series of papers analyzing the specificity of action of the various chemical and biological immunosuppressive agents on the blastogenic responses of T and B lymphocytes, optimal concentrations of cells and blastogenic substances and other parameters were tested, and the kinetics of transformation was investigated in detail.

Bacterial endotoxins: comparison of mitogenic, polyclonal, antibody-inducing and toxicity activities