T-cell independent reconstitution of the immunoglobulin levels in nu/nu mice.

Nude mice (BALB/c, H-2d) were transplanted under the renal capsule either with allogeneic (CBA, H-2k; C57B1/6, H-2b) or human thymus that were long-term precultured or pretreated in vitro with Carrageenan for three days. None of the thymus tissue transplants showed lymphatic repopulation 9 wk after transplantation. Histological investigation of the peripheral lymphatic tissue did not reveal any change in the thymus-dependent area. On the other hand, plasma cells and germinal centers could be found in significantly increased numbers. In addition, a normalization of the serum immunoglobulin concentrations could be found, as no specific antibodies against thymus-dependent antigens were present after immunization and T-cell function did not improve. Similar results were obtained 9 wk after injection of irradiated thymocyte suspensions or of peritoneal macrophages from immunocompetent donors. It is concluded that thymus epithelial cells could act via macrophages on the polyclonal maturation and differentiation of B cells without involvement of T cells. This would be in agreement with the experience in some patients with severe combined immunodeficiency (SCID) in which reconstitution of the immunoglobulin levels is observed after transplantation of cultured thymus tissue before T-cell reconstitution can be demonstrated.