The role of lymphoid cells in bone resorption: Cellular immunological competence in ia rats

The ia (incisors absent) rat is a naturally occurring mutant that has osteopetrosis resulting from reduced bone resorption. A number of in vestigators have reported that other osteopetrotic mutant rats (op) and mice (mi and op), in addition to demonstrating the skeletal manifestations of the disease, have cellular immunological defects. In light of the fact that bone resorption has been demonstrated to be controlled by hematopoietic tissues and more specifically by mononuclear cells isolated from lymphoid organs, it seemed appropriate to investigate immunological competence in the ia rat, to determine whether or not it had this defect in common with the op rat. Contrary to the results presented for other osteopetrotic mutants, we found that the thymuses in our ia mutants had a normal cellular composition and the T-cell-dependent zones in the lymph nodes were not deficient in lymphocytes. Therefore, this study was undertaken to investigate the response of ia rats to oxazolone, which produces one type of T-cell-dependent immune response, delayed hypersensitivity. The results of these studies indicate that ia rats at 18 days of age have the ability to develop delayed hypersensitivity, as shown by both a blastogenic response in the lymph node draining the site of sensitization and a positive skintest. The magnitudes of these responses were similar in ia and normal littermates, both histologically and quantitatively. Therefore, the ia mutant does not appear to have a defect of the thymus-dependent immune system, and further studies should be carried out to investigate other parameters of immunological competence in these animals.