Plasmodium falciparum: an invasion inhibitory human monoclonal antibody is directed against a malarial glycolipid antigen.

A Plasmodium falciparum malaria blood stage antigen was detected using a human monoclonal antibody (MAb A52A6) obtained from a clinically immune donor. Immunofluorescence analysis showed that the MAb reacted with the intracellular parasite throughout the asexual blood stage cycle as well as with gametocytes. The MAb also reacted with the surface of erythrocytes containing late stage P. falciparum parasites. The antigen seen by the MAb was species- but not strain- or isolate-specific. At rupture of the infected erythrocytes, antigenic material was deposited on the membrane of uninfected cells surrounding the parasite. At merozoite invasion MAb reactive material was present on the invaginating erythrocyte membrane, indicating an involvement of the antigen in the invasion process. This was also indicated by the high capacity of the MAb to inhibit merozoite invasion in vitro. The antigen appears to be a phosphoglycolipid, sensitive to phospholipase and present in lipid extracts of P. falciparum-infected erythrocytes.