Regulation of macrophage agglutination factor production by alpha 2-macroglobulin

Alpha-2-macroglobulin (alpha 2M) is a major mammalian plasma proteinase inhibitor and a well-established suppressor of T cell blastogenesis. Its role in modulating T cell-mediated lymphokine production is less well documented. We have isolated and characterized guinea-pig plasma alpha 2M in order to study its role in regulating the elicitation of macrophage agglutination factor (MAggF), a T cell-dependent inflammatory lymphokine closely related to fibronectin. Alpha-2-macroglobulin was purified by a combination of gel chromatography and immunoadsorption to remove contaminating IgM. Purified alpha 2M showed a double band on polyacrylamide gel electrophoresis. It had a molecular weight of 714,000 which fell to 190,000 on reduction, a pI of 4.8 and bound up to 1.3 moles of trypsin or elastase per mole. The elicitiation of MAggF from 25 X 10(6) purified protein derivative (PPD)-stimulated guinea-pig lymph node cells was inhibited 99% by 2-3 micrograms of biologically active alpha 2M only if the proteinase inhibitor was added to the lymph node cells at the same time as antigen. No inhibition of MAggF production was observed when active alpha 2M was added at the end of culture or when biologically inactive alpha 2M was added to the cultures at any time. MAggF was not elicited from normal cells by PPD, nor did alpha 2M have any effect on these cultures. Purified alpha 2M had no direct effect on MAggF activity in culture supernatants. We suggest that alpha 2M may be involved in modulating antigen-elicited lymphokine production in vivo.