Immune changes in humans during cold exposure: effects of prior heating and exercise

This study examined the immunological responses to cold exposure together w ith the effects of pretreatment with either passive heating or exercise (wi th and without a thermal clamp). On four separate occasions, seven healthy men [mean age 24.0 +/- 1.9 (SE) yr, peak oxygen consumption = 45.7 +/- 2.0 ml . kg(-1) . min(-1)] sat for 2 h in a climatic chamber maintained at 5 de grees C. Before exposure, subjects participated in one of four pretreatment conditions. For the thermoneutral control condition, subjects remained sea ted for 1 h in a water bath at 35 degrees C. In another pretreatment, subje cts were passively heated in a warm (38 degrees C) water bath for 1 h. In t wo other pretreatments, subjects exercised for 1 h at 55% peak oxygen consu mption (once immersed in 18 degrees C water and once in 35 degrees C water) . Core temperature rose by 1 degrees C during passive heating and during ex ercise in 35 degrees C water and remained stable during exercise in 18 degr ees C water (thermal clamping). Subsequent cold exposure induced a leukocyt osis and granulocytosis, an increase in natural killer cell count and activ ity, and a rise in circulating levels of interleukin-6. Pretreatment with e xercise in 18 degrees C water augmented the leukocyte, Granulocyte, and mon ocyte response. These results indicate that acute cold exposure has immunos timulating effects and that, with thermal clamping, pretreatment with physi cal exercise can enhance this response. Increases in levels of circulating norepinephrine may account for the changes observed during cold exposure an d their modification by changes in initial status.