The immune response by lymphoid cells in vitro.

Bone marrow cells obtained from normal unimmunized rabbits were stimulated to undergo blastogenesis and mitosis and to incorporate tritiated thymidine upon incubation with various protein antigens in vitro. Call suspensions of other lymphoid organs, obtained from normal rabbits, failed to respond in this fashion. This in vitro response did not occur with bone marrow cells of immunized rabbits, although it was observed with lymph node and spleen cells obtained from previously immunized rabbits. The immune nature of the bone marrow blastogenic response was demonstrated by the detection of specific antibody, by the fluorescent antibody technique, within the stimulated cells. The response of the bone marrow cells was localized to the lymphocyte-enriched cell fraction following centrifugation of the whole bone marrow in a linear sucrose density gradient. The findings suggest that the bane marrow lymphocyte plays an important role during the induction of a primary immune response