The relationship between group A and group C meningococcal polysaccharides and serum opsonins in man

The interaction in vitro between human granulocytes and meningococci in the presence of sera from volunteers immunized by Gotschlich et al. with purified group A and group C meningococcal polysaccharides was studied. Phagocytosis of meningococci did not occur in the presence of preimmunization sera. In all volunteers tested, group-specific opsonins were detected in groups A and C polysaccharide antisera. Opsonic activity appeared within 1 wk after immunization and persisted for at least 14 months. Titers of opsonic activity ranged from 1:20 to 1:320; highest titers were noted in 2-4 wk antisera. Meningococcal opsonins were detected in both 19S and 7S immunoglobulins. Opsonic activity in low-titer antisera depended on heat-labile factors present in both normal and immune sera, whereas phagocytosis was observed in the presence of heat-inactivated high-titer antisera. Phagocytosis of group A meningococci in the presence of certain group A polysaccharide antisera was inhibited by N-acetyl mannosamine, but not by mannose, mannosamine, N-acetyl glucosamine, N-acetyl galactosamine, or N-acetyl neuraminic acid. Absorption studies with sera from patients with natural meningococcal infections revealed that these polysaccharides are the major antiphagocytic determinants for group A and group C meningococci. These studies are consistent with previous reports suggesting that immunization with group A and group C polysaccharides may well provide group-specific protection against meningococcal infections.