Alterations in the mitogen responsiveness of lymphocytes from mice bearing Moloney sarcoma virus induced tumors.

The effects of Moloney Sarcoma Virus (MSV) induced tumor growth dynamics on the blastogenic responsiveness of lymphocytes from BALB/c mice were investigated. Lymphocytes from spleen, thymus and lymph node pools were tested for responsiveness to phytohemagglutinin (PHA) and concanavalin A (Con A). Results showed a significant decrease in PHA-induced blastogenesis of all lymphocytes tested at the time of maximal tumor volume, with a return to normal responsiveness as the tumor regressed. In contrast, a differential dose dependent Con A response occurred in spleen and thymus lymphocytes. A decreased 3H-thymidine uptake occurred at optimal Con A dose, correlating with the PHA decrease. However, at a lower Con A dose an increased response was observed, beginning shortly before the PHA depression and continuing until regression of tumor began. This phenomena was not observed in lymph node lymphocytes. Based upon these observations, we suggest that the cell or cells responsible for the transient suppression of PHA responsiveness may be Con A responsive T lymphocytes.