Is the Acquired Homologous Immunity to P. Vivax Equally Effective against Sporozoites and Trophozoites? 1

Abstract

In extending our studies of the characteristics and properties of the homologous immunity to P. vivax acquired as a result of recovery from a naturally induced (sporozoites from mosquitoes) infection, it appeared desirable to ascertain whether this defensive mechanism, which is characteristically directed against the trophozoites, is also operative against sporozoites. We have previously (1) shown that homologous immunity is not perfect, in that it cannot prevent reinvasion by the parasites with their subsequent reproduction, although limiting their effective multiplication so they rarely, if ever, attain a density sufficient to produce more than a slight clinical attack. Our early experiments on immunity (2) dealt with the reinoculation, by natural means, of patients who had recovered from naturally induced attacks, while other experiments later conducted along similar lines, have all shown that the immunity arising from a naturally induced attack does not prevent appreciable although subclinical increase in the density of trophozoites following natural reinoculation.