The immune status of the rat with carcinoma of the bowel.

Studies were made to determine whether rats receiving 1,2-dimethylhydrazine (DMH) to induce bowel cancer were immunologically compromised during tumour development. General cellular immunodepression was observed in DMH rats in nonspecific assays of T-cell and killer-cell (K-cell) function and later in allograft response and in vitro tumour immunity tests. B-cell levels in local lymph nodes increased significantly very late in tumour growth. It is suggested that DMH itself was exerting immunosuppressive as well as carcinogenic effects while it was administered. After withdrawal of DMH some immune faculties (tumour immunity, B-cell response) reappeared, so it is unlikely that the immune suppression observed was a result of factors produced by the developing neoplasm. There are indications that DMH administration in the rat is immunosuppressive and that tumour growth may be facilitated by this action and not by tumour reactive lymphocytic depletion or paralysis associated with blocking factors or suppressor cell production.