Cotton bract tannin: a novel human T-lymphocyte mitogen and a possible causative agent of byssinosis.

Cotton bract tannin, a major organic component of cotton dust, was tested for mitogenic activity upon human T lymphocytes. Tannin caused polyclonal activation of human T lymphocytes in vitro. The pattern of T-cell response to tannin was similar to the pattern seen in lymphocytes stimulated with the well-known plant lectin T-cell mitogens, PHA and ConA. The response to tannin was shown to be dependent upon tannin dose and presence of monocytes. The maximum response occurred after 3-4 days in culture with the magnitude comparable to the one achieved by ConA. Lipopolysaccharide from Enterobacter agglomerans, a major contaminant of cotton dust, was shown not to be a mediator of tannin mitogenicity in vitro. A role for tannin as a polyclonal cell activator and, therefore, a possible etiologic agent of byssinosis is suggested by these observations.