Cells involved in the immune response. XXVI. The demonstration of bone marrow-specific antigens in the rabbit

Horse anti-rabbit bone marrow cell antiserum was tested for its cytotoxic activity with respect to the lymphocytes of the various lymphoid organs. The unabsorbed antiserum was highly cytotoxic with respect to the circulating WBC and cells of the bone marrow and thymus but demonstrated low cytotoxic activity with respect to spleen, lymph node and SAPP cells (sacculus rotundus, appendix and Peyer's patches). However, following absorption with thymocytes, lymph node cells or SAPP cells, cytotoxic activity directed toward any of these cell types disappeared without affecting the cytotoxic activity with respect to bone marrow and circulating lymphocytes. On the other hand, bone marrow and spleen cells and circulating white blood cells were capable of absorbing out completely the cytotoxic activity directed toward these cells. On the basis of a comparison of efficiency of absorption of anti-bone marrow cell activity by cells of the different lymphoid organs and cytotoxicity assays of the absorbed antiserum, it is concluded that approximately 15–25 per cent of the spleen lymphocytes and 20–40 per cent of the circulating lymphocytes in the rabbit are bone marrow-derived cells. The other lymphoid organs do not normally appear to possess these cells.