A polysaccharide (PS) from the venom of a tropical ant interacts with a human nonimmunoglobulin protein(s) in serum, causing C1 activation and the consumption of the functional activity of C4 and C2 (D. R. Schultz, P. I. Arnold, J. Immunol., in press). We now describe these studies in more detail.

The PS had a heterogeneous size in native ant venom. The smallest moiety that activated serum C1 had a m.w. of ca. 3,000 as determined by gel chromatography. The PS was not precipitated by barium salts, showing no apparent sulfate groups. The following sugars and the molar ratios were found by gas chromatography: mannose (7.7), fucose (1.8), N-acetylgalactosamine (1.6), galactose (1.4), glucose (1.0), and N-acetylglucosamine (1.0).

Evidence showing that a serum β-lipoprotein (B-LP) participates with venom PS to cause activation of C1 includes: 1) The PS caused a visible precipitation when incubated with normal human serum or its highly purified B-LP at 37°C for 12 hr.

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