title: Concomitant but not causal association between surface charge and inhibition of phagocytosis by cryptococcal polysaccharide.
abstract: The mechanism by which capsular polysaccharides inhibit phagocytosis is not clearly understood. We investigated the association between a negative surface charge and inhibition of phagocytosis by the capsular polysaccharide of Cryptococcus neoformans. A two-polymer aqueous-phase system containing phosphate ions was used to assess surface charge. Opsonins such as normal bovine serum and normal human immunoglobulin G reduced the surface charge on non-encapsulated cryptococci and simultaneously enhanced phagocytosis. These same opsonins had no effect on phagocytosis or surface charge of encapsulated cryptococci. F (ab')(2) fragments of normal human immunoglobulin G neither enhanced phagocytosis nor altered the surface charge of non-encapsulated cryptococci. Addition of purified cryptococcal polysaccharide to non-encapsulated cells inhibited phagocytosis of the yeast and induced a strong negative charge at the yeast surface. Chemical modification to reduce the surface charge of either purified cryptococcal polysaccharide or intact encapsulated cryptococci produced a small loss of phagocytosis-inhibiting activity; however, all treated polysaccharide preparations retained a significant ability to inhibit phagocytosis of the yeast. These results indicated that the association between surface charge and inhibition of phagocytosis was largely circumstantial, and presence of a negative surface charge could not account for the powerful antiphagocytic action of cryptococcal polysaccharide.
mesh_terms: D002462:Cell Membrane / Q000276:immunology / Q000502:physiology*; D003454:Cryptococcus / Q000276:immunology*; D003455:Cryptococcus neoformans / Q000276:immunology*; D007074:Immunoglobulin G / Q000276:immunology; D009895:Opsonin Proteins / Q000276:immunology; D010587:Phagocytosis / Q000187:drug effects; D011134:Polysaccharides / Q000276:immunology* / Q000494:pharmacology; D013499:Surface Properties
chemical_list: D007074:Immunoglobulin G; D009895:Opsonin Proteins; D011134:Polysaccharides