Cells Involved in T H E Immune Response Vi. the I~¢une Response to Red Blood Cells in I.rradiatfa) Rabbles after Administration 0~" Normal, Primed, or ]'mmune Allogeneic Rabbit Bone Marrow Cells* by Nabih

In previous communications from this laboratory (1, 2) it was demonstrated that bone marrow cells of normal rabbits are capable of undergoing blastogenesis and mitosis upon incubation with a large number of antigens in vitro. Antibody formation by the bone marrow cells in vitro was detected by the fluorescent antibody technique (2). When a relatively large dose of an antigen was injected into a rabbit and the bone marrow removed 24 hr later, the capacity of these cells to respond to the specific antigen in vitro was lost, although the response to other non-cross-reactive antigens was intact. The injection of a lesser amount of the antigen into the donor resulted in a lengthening of the time required for the bone marrow to lose the capacity to respond to the specific antigen in vitro. Fractionation of normal bone marrow cells on a sucrose density gradient permitted the separation of a fraction high in concentration of lymphoid cells and a fraction of bone marrow containing the majority of myeloid and erythroid precursors. The former was very reactive when exposed to antigens in vitro, whereas the latter reacted only weakly in response to antigenic stimulation in vitro (2, 3). Since, of all the lymphoid tissues of the normal rabbit, only the bone marrow lymphoid cells demonstrated this capacity to react with antigens in vitro, it was concluded that the committed immunocompetent cells originate in the bone marrow of the rabbit and that they vacate the bone marrow shortly after their interaction with the particular antigen (2). We have now confirmed and extended these original observations using a cell transfer system. I t has been demonstrated, in the experiments presented below, that irradi-