Physiochemical characterization of human histamine-induced suppressor factor

Abstract

A product of histamine-stimulated human lymphocytes, histamine-induced suppressor factor or HSF, was characterized by enzyme treatment, sensitivity to reduction and alkylation, by molecular sieve chromatography, and by polyacrylamide gel electrophoresis. HSF was found to have a wide pH stability (pH 3–10), sensitivity to temperatures greater than 80 °C, and to have the properties of a glycoprotein by virtue of its sensitivity to chymotrypsin, trypsin, sodium periodate, and neuraminidase. HSF did not appear to have a serine group(s) in its “active” site since its biologic activity remained intact following treatment with an irreversible serine esterase inhibitor (phenylmethylsulfonyl fluoride). Further, HSF did not appear to have inter- or intramolecular disulfide linkages because treatment with denaturing and/or reducing agents, followed by alkylation, did not significantly alter its activity. Molecular sieve chromatography employing Sephadex G-100 revealed an apparent molecular weight for HSF of 25–40,000. Electrophoresis of HSF in polyacrylamide gels at pH 8.7 under nonreducing conditions revealed two regions of activity, one region migrating with albumin and the other region anodal to albumin. In addition to suppressing lymphocyte proliferation, the 25–40,000 M r, Sephadex G-100 fractions also inhibited the production of leukocyte inhibitory factor. Of particular interest, gel filtration of supernatants generated by stimulating mononuclear cells with either histamine, dimaprit (but not 2-pyridylethylamine), concanavalin A, or Candida albicans resulted in similar elution profiles with regard to inhibition of lymphocyte proliferation. That is, 25–40,000 M r fractions of supernatants generated by each stimulant suppressed lymphocyte proliferation to a similar degree. The latter findings provide indirect evidence that T lymphocytes, triggered in response to antigenspecific and nonspecific stimuli, elaborate suppressor molecules capable of modulating T-cell function that share certain similarities.