In vitro antigenic stimulation of peripheral blood and lymph node lymphocytes of sensitized guinea-pigs; the effect of a second administration of antigen in vivo.

Stimulation of DNA synthesis by a guinea-pig albumin—orthanilic acid conjugate (AO) and by tuberculin purified protein derivative (PPD) was obtained in cultures of peripheral blood and lymph node lymphocytes from guinea-pigs with delayed hypersensitivity to these antigens. Animals sensitized to both AO and PPD were given a further injection of 5 μg AO, intravenously, 8 hours before killing for studies. In these guinea-pigs, peripheral blood cultures, but not lymph node cultures, showed greater DNA synthesis in response to both AO and PPD than cultures from controls not given a further injection of AO. It is suggested that the further increase in DNA synthesis was due to non-specific lymphocyte `activation' following the interaction of antigen and specifically sensitized lymphocytes.