Peripheral T lymphocytopenia under exogenous thermal stress.

A transient decrease in T lymphocytes in peripheral blood was observed in twelve healthy volunteers immersed in hot water baths which raised their mean rectal temperature by 1.35 C. T lymphocytes declined from 59 to 41 rel % (2p less than 0.001) or from a mean of 1990 to 1300 per mm3. T lymphocytopenia was accompanied by a relative increase in the fraction of B lymphocytes. Total lymphocyte count remained unchanged. In vitro heating alone to 39 C did not influence the total of SRBC-labelled lymphocytes. The findings are interpreted to be the result of a change in lymphocyte distribution with increased recirculation of mobile T lymphocytes.