PHOSPHOLIPIDS COUPLED TO A CARRIER INDUCE IGG ANTIBODY THAT BLOCKS TUMOR-NECROSIS-FACTOR INDUCTION BY TOXIC MALARIA ANTIGENS

Phospholipid-containing antigens of malaria parasites stimulate macrop hages to secrete tumour necrosis factor (TNF), induce hypoglycaemia an d are toxic to mice. This TNF induction is inhibited by antisera made against the antigens, the inhibitory activity of which can be removed specifically by adsorption to phosphatidylinositol (PI) liposomes. Alt hough the same was true of antisera made against PI, the inhibitory ac tivity of antisera made against some other phospholipids appeared to b e directed against a common determinant, probably the phosphate ester head group. We have shown previously that the activity of all the anti sera was associated mainly with IgM and was not boosted by repeated in jections of the antigens. To try and induce a secondary response again st the parasite antigens using non-toxic molecules, mice were immunize d with various phosphorylated compounds coupled to keyhole limpet haem ocyanin (KLH). Three injections of PI-KLH or of phosphatidyl-serine (P S) coupled to KLH induced significantly higher titres of inhibitory an tibody than one; furthermore, the inhibitory activity was mainly in th e IgG fraction. The antisera did not inhibit TNF induction by lipopoly saccharide (LPS) or lipoteichoic acid. However, antisera against PS-KL H, though not PI-KLH, inhibited the induction of TNF by the phospholip id, platelet-activating factor (PAF). These antisera, and antisera fro m mice immunized with phospho-threonine or galactosamine-1-phosphate c onjugated to KLH, contained inhibitory antibodies of differing specifi cities. Mice immunized with PI-KLH, PS-KLH or phospho-threonine-KLH di d not develop hypoglycaemia when challenged with the parasite toxic an tigens. These results indicate that the antigenicity of non-toxic anal ogues can be dramatically enhanced by coupling to a protein carrier.