Induction of interleukin-1-beta release from human monocytes by cotton bract tannin

The human T lymphocyte proliferative response to cotton bract tannin was shown to be dependent upon the presence of monocytes. Since monocytes support the T cell mitogenic response by interleukin-1 (IL-1) production, it was anticipated that tannin has IL-1-inducing ability. To examine this possibility, human monocytes were cultured alone or with peripheral blood T lymphocytes, and stimulated with tannin. Control cultures included unstimulated cells, and cells challenged with other IL-1 inducers: concanavalin A (Con A) and lipopolysaccharide from Escherichia coli or Enterobacter agglomerans. IL-1 beta was measured in culture supernatants 24 h after initiation of the culture by the use of an ELISA or an RIA. The results showed that tannin stimulated monocytes to secrete IL-1 beta in a manner similar to Con A, i.e. substantially more cytokine was measured in the supernatants of monocyte-T-lymphocyte co-cultures than in the cultures of monocyte alone. Endotoxin from E. coli was less effective than the endotoxin from E. agglomerans in IL-1 induction. Contaminating endotoxin present in the tannin preparation accounted for the majority of IL-1 beta released from monocytes alone stimulated with tannin, but only 20% of the IL-1 beta released from tannin-stimulated monocyte-T-lymphocyte co-cultures. These results show that tannin itself has IL-1-inducing ability. The dose-response studies show that the extent of IL-1 beta release is dependent on tannin dose and that increased levels of monocyte-produced IL-1 beta precede the increase in T lymphocyte proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)