BINDING OF RECOMBINANT INTERLEUKIN-1-BETA TO THE 3RD COMPLEMENT COMPONENT AND ALPHA-2-MACROGLOBULIN AFTER ACTIVATION OF SERUM BY IMMUNE-COMPLEXES

  • 15 June 1990
    • journal article
    • research article
    • Vol. 75  (12) , 2388-2395
Abstract
Activation of human normal serum with tetanus/antitetanus immune complexes (TAT-IC) resulted in increased binding of 125I-labeled interleukin-1.beta. (IL-1.beta.) to serum factors, as opposed to untreated serum. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by autoradiography showed labeling of two large molecular mass factors of an apparent molecular weight (Mr) of 200,000 and 400,000, respectively. These complexes could be dissociated by reduction. No complexes were formed when reducing compounds were added to serum-TAT-IC-125I-IL-1.beta. mixtures. Complex formation was largely prevented by alkylating compounds. Molecular sieve chromatography of TAT-IC-activated serum confirmed that 125I-IL-1.beta. became bound to the high Mr serum proteins. Fractions containing high molecular 125I-IL-1 serum protein complexes partially retained IL-1-like activity since they induced proliferation of an IL-1-dependent murine T helper (D10G4) cell lineage. The 125I-IL-1.beta. bindingfactors could be immunoprecipitated from TAT-IC-activated serum 125I-IL-1.beta. solutions by antisera to .alpha.2-macroglobulin (.alpha.2M) or to the third complement component (C3), SDS-PAGE of the immunoprecipitates showed radioactive bands corresponding to the expected Mr resulting from complex formation between 125I-IL-1.beta. and these two proteins. Treatment of purified plasma .alpha.2M and C3 with trypsin or activation with methylamine, which cause cleavage of the internal third ester and the appearance of free thiol groups in these proteins, mediated binding of 125I-IL-1.beta. to .alpha.2M and C3b. The results suggest that cleavage of the internal thiol ester in C3 and .alpha.2M makes these plama proteins susceptible to binding of 125I-IL-1.beta. and that free thiol groups do play a role in the formation of 125I-IL-1.beta. plasma protein complexes. Activated C3 and .alpha.2M may function as IL-1.beta. carrier proteins in biologic fluids, in addition to their other physiologic roles.

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