In vitro responses of rat lymphocytes following adult thymectomy. II. Increased inhibition by splenic adherent cells of responses to phytohemagglutinin

Adult thymectomy in rats results in a marked fall of spleen cell responsiveness to PHA over a period of days to weeks. Examination of dose-response curves showed that, with high PHA dose or ≥ 10⁶ cells/ml, there is a profound inhibition of the response with spleen cells from thymectomized animals compared with cells of matched sham-operated controls. However, when adherent cells are removed from the cell suspensions, the remaining nonadherent cells give an almost linear dose-response relationship with increasing PHA similar to that exhibited by the nonadherent cells of the controls or sometimes a slightly decreased response. Similarly, when increasing numbers of spleen cells from these animals are cultured (with admixed thymocytes to make a constant total of 2 × 10⁶ cells/ml) with PHA, the linear portion of the doseresponse curve can be extrapolated to give a similar value for the maximal potential response, which again is the same as or somewhat less than the corresponding value for sham-operated controls. A difference in inhibitory capacity is also shown in mixtures of the two spleen cell populations with LNC or with purified spleen cells. It is concluded that adult thymectomy results in increased “suppressor” activity in the spleen within a few days and may reduce slightly the number of T lymphocytes in the spleen reactive with PHA.