Interleukin-1 alpha in human sweat is functionally active and derived from the eccrine sweat gland

We wished to establish the presence of interleukin-1 (IL-1) in human sweat (5) and clarify its origin and mechanism of secretion. IL-1 alpha concentration ([IL-1 alpha]) in clean sweat from the back increased with the sweat rate, plateauing at the maximal sweat rate ([IL-1 alpha]max). The mean [IL-1 alpha]max was 545 pg/ml (n = 17) for men and 1,324 pg/ml for women in back sweat. The mean [IL-1 alpha]max for axillary sweat in men was 1,568 (n = 6). Palmar sweat was 9.2 ng/ml (n = 5) for IL-1 alpha and 7.9 ng/ml for IL-1 beta. [IL-1 alpha]max decreased to one-third that of the first sweat test, when second sauna sweat tests were conducted after 2 h of continuous sweating on the same day. Western blot analysis of the purified sweat IL-1 alpha fraction revealed bands at 17, 29, and 33 kDa. Immunoreactive IL-1 alpha was localized mainly in the secretory coil lumen, intercellular canaliculi, cytoplasm, mitochondria, and near plasma membranes. Polymerase chain reaction revealed the presence of IL-1 alpha mRNA in the sweat gland and in cultured human eccrine secretory coil cells. Both sweat IL-1 alpha and human recombinant IL-1 alpha at 500 pg/ml strongly stimulated interleukin-6 and interleukin-8 production in cultured fibroblasts. We conclude that the IL-1 alpha-like immunoreactive substance in sweat is IL-1 alpha itself, is derived from the sweat gland, and is biologically active at concentrations normally present in fresh sweat.