Screening of various immunopotentiators in spontaneously hypertensive rats with T-cell depression.

A strain of SHR which develops hypertension spontaneously is marked by a selective depression of T-cell functions associated with an early appearance of natural thymocytotoxic autoantibody and a deficiency of thymic hormone. Present results demonstrate that various immunopotentiators (IPs) such as thymostimulin (TS), PS-K, SPG, neurotropin (NSP), and K-247 partially or almost completely reversed the T-cell depression in these SHR as detected by a rosette forming test, plaque-forming assay and blastogenesic response to PHA and Con A. In contrast, these IPs had no effect on the immune responsiveness of WKA rats with normal T-cell functions. Among the IPs, NSP, which had an almost complete restorative effect on the T-cell functions of SHR, induced significant transplantation resistance to the syngeneic tumor challenge. A new synthetic product K-247 also induced a significant suppression of lethal tumor growth in SHR, though its restorative effect on T-cell functions was weak. The fact that K-247 had a suppressive effect on tumor cell growth in vitro indicates that biochemical modifications rather than immunological ones may be involved. However, none of the IPs induced antitumor resistance in normal WKA rats. These results suggest that this strain of SHR provides a useful animal model for evaluation of various IPs.