Abstract
Glutamate was recently found to inhibit the membrane transport of cystine and to impair the function of macrophages and lymphocytes in vitro. Elevated plasma glutamate concentrations in patients with advanced carcinoma were also found to be quantitatively correlated with reduced lymphocyte reactivity in these persons. We now investigated the questions whether glutamate levels in tumor patients would decline to approximately normal levels after tumor resection and, if so, whether this would be correlated with a recovery of lymphocyte reactivity. We report that plasma glutamate levels as well as the concomitantly elevated plasma lactate levels of patients with colorectal carcinoma return to practically normal levels within 1 week after curative surgery. This is accompanied by a rapid recovery of the lymphocyte reactivity against concanavalin A. Lymphocyte responses against pokeweed mitogen and phytohemagglutinin, in contrast, remain impaired for at least 6 months, indicating that elevated glutamate levels in patients with colorectal carcinoma are associated with a long-lasting defect in the immune system.