Differential Induction of Membrane‐Associated Interleukin 1 (IL‐1) Expression and IL‐1α and IL‐1β Secretion by Lipopolysaccharide and Silica in Human Monocytes

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Abstract
Bacterial lipopolysaccharide (LPS) and silica dust arc known to be effective inducers of interleukin 1 (IL‐1) in human cultured monocytes. The data reported here show that although the levels of secreted IL‐1 were equally high after in vitro stimulation with an optimal dose of LPS or silica, there were two clear differences: (i) the levels of membrane‐associated IL‐1 (as detected by the comitogenic effect of paraformaldehyde (PFA)‐fixed cells or purified membrane fragments on marine thymocytes) were ca. five times higher after LPS stimulation than after silica stimulation, (ii) the secreted IL‐1 after LPS stimulation was mainly of the pI 7 (IL‐1β) type, while after silica stimulation there were equally high amounts of pI 7 and pI 5 (i e. IL‐1α) forms. In both cases the IL‐1‐active molecules belonged to the 15 kDa class. These data show that the nature of the activating agent has a clear influence on the distribution of the biologically active IL‐1 molecules. Moreover, the finding that after silica stimulation the amount of membrane‐associated IL‐1 (which was recently shown to be of the IL‐1α type) was low, while IL‐1α in the culture Quid was clearly elevated, suggests that the IL‐1α not attached to the cell membrane (or released from it) significantly contributes to the secreted IL‐1 pool.