ACUTE PLASMODIUM-CHABAUDI CHABAUDI MALARIA INFECTION INDUCES ANTIBODIES WHICH BIND TO THE SURFACES OF PARASITIZED ERYTHROCYTES AND PROMOTE THEIR PHAGOCYTOSIS BY MACROPHAGES IN-VITRO

CBA/Ca mice infected with 5 x 10(4) Plasmodium chabaudi chabaudi AS-pa rasitized erythrocytes experience acute but self-limiting infections o f relatively short duration. Parasitemia peaks (similar to 40% infecte d erythrocytes) on day 10 or 11 and is then partially resolved over th e ensuing 5 to 6 days, a period referred to as crisis. How humoral and cellular immune mechanisms contribute to parasite killing and/or clea rance during crisis is controversial. Humoral immunity might be parasi te variant, line, or species specific, while cellular immune responses would be relatively less specific. For P. c. chabaudi AS, parasite cl earance is largely species and line specific during this time, which s uggests a primary role for antibody activity. Accordingly, acute-phase plasma (APP; taken from P. c. chabaudi AS-infected mice at day 11 or 12 postinfection) was examined for the presence of parasite-specific a ntibody activity by enzyme-linked immunosorbent assay. Antibody bindin g to the surface of intact, live parasitized erythrocytes, particularl y those containing mature (trophozoite and schizont) parasites, was de monstrated by immunofluorescence in APP and the immunoglobulin G (IgG) -containing fraction thereof. Unfractionated APP (from P. c, chabaudi AS-infected mice), as well as its IgG fraction, specifically mediated the opsonization and internalization of P. c. chabaudi AS-parasitized erythrocytes by macrophages in vitro. APP from another parasite line ( P.c, chabaudi CB) did nest mediate the same effect against P, c. chaba udi AS-parasitized erythrocytes. These results, which may represent on e mechanism of parasite removal during crisis, are discussed in relati on to the parasite variant, line, and species specificity of parasite clearance during this time.