ACQUIRED TOLERANCE TO SKIN HOMOGRAFTS IN MICE

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Abstract
Acquired tolerance to CBA skin homografts is lost in many C3H mice neonatally injected with CBA spleen cells. The skin homografts persist for at least 2 months but then exhibit a chronic rejection pattern. Histological analysis of the lymphoid tissues reveals the onset of an immune response in the axillary lymph nodes of many 4-month-old tolerant mice. This immune response which appears before external indications of graft rejection, is manifested as an increase in number of germinal centers and plasma cells. During graft contraction and shortly after graft rejection, the immune response is still limited to the lymph nodes. After rejection of a second graft by post-tolerant mice, histological indications of an immune response are also found in the spleen. The data suggest the development of a host-versus-graft reaction in seemingly tolerant C3H mice, which increases in severity with age. The results are discussed from the point of view that tolerance is dependent upon a critical balance between the immune potential of the host and the population of donor cells. As mice mature, their immune potential may increase. The resulting host-versus-graft reaction increases, culminating in the loss of tolerance.