The chemical mediation of delayed hypersensitivity skin reactions: III. Purification and characterization of a precursor protein for macrophage-chemotactic factor in normal guinea pig plasma.

A putative precursor protein for macrophage-chemotactic factor, which was extracted fro inflammatory skin sites (MCFS-1) (Kambara et al, Am J Pathol 1977, 87:359-374), was found in normal guinea pig plasma and was purified to an apparent homogeneity upon SDS-polyacrylamide gel electrophoresis with a molecular weight of 160,000. This plasma protein was different from complement components of C3 and C5 in terms of molecular weight, functional activity as complements detected by hemolytic assay, and immunologic properties. Although it exhibited the common antigenicity with MCFS-1, it did not show any chemotactic activity for macrophages, However, incubation of this plasma protein at either 4 C for 5 days or 37 C for 1-2 days could generate a chemotactic factor with a molecular weight of approximately 150,000 which was similar to that of MCFS-1. This generation of chemotactic activity was completely prevented by the presence of the serine-type protease inhibitor, phenylmethylsulfonyl fluoride. These data could be well accounted for if we assume that this plasma protein might be a precursor for the macrophage-chemotactic factor found in delayed hypersensitivity skin sites, and that a proteolytic process might be involved in the activation of this precursor.