Stimulation of early protein synthesis as an assay of immune reactivity: Analysis of the cells responding to mitogens and alloantigens

Spleen cells from nonimmune mice were cultured for 24 hr in the presence of phytohemagglutinin (PHA), lipopolysaccharide (LPS), or alloantigens. Data are presented to show that within this time period all 3 stimuli caused an increase in protein synthesis. The response to PHA and alloantigens was defined as a T cell response by virtue of the effects of anti theta antibody, adult thymectomy, and velocity cell sedimentation. Similarly, the response to LPS was determined to be a B cell response since it was unaffected by anti theta antibody or adult thymectomy but was abolished by treatment of responder cells with anti Ig antiserum and complement. Furthermore, the cells responding to LPS were physically separable from those responding to PHA and alloantigens and sedimented with a velocity characteristic of B lymphocytes.