CROSS-REACTIVE CELLULAR IMMUNE-RESPONSE TO CIRCUMSPOROZOITE PROTEINS OF PLASMODIUM-VIVAX AND PLASMODIUM-FALCIPARUM IN MALARIA-EXPOSED INDIVIDUALS

Acquired immunity against the recombinant circumsporozoite protein of P. falciparum (rPfCS) or P. vivax (rPvCS) was studied in two malarious areas of the Brazilian Amazon. Cellular responsiveness, evaluated by proliferative assays, was detected in about 45% of individuals who had recovered from recent acute malaria infections. Peripheral blood mono nuclear cells of individuals whose last malaria infection was by P. vi vax responded more to the rCS proteins than those who had P. falciparu m. Since in P. vivax infections hypnozoites in the liver retain CS ant igen, this stage may have contributed to the increased cellular respon se. The unexpected result was that in primoinfections by P. falciparum or P. vivax the proliferative response did not correspond to the rPfC S and rPvCS, respectively. Furthermore, among the malaria-exposed indi viduals, there was a positive correlation between the intensity of the responses to the two rCS proteins. Our results suggest that cross-rea ctive epitopes exist in the CS protein of P. falciparum and P. vivax. In the areas studied, the frequency of antibodies against rPvCS and/or rPfCS ranged from 43% to 11%. Species-specific antibodies against the CS protein were detected in the primoinfected individuals. Some indiv iduals living in the endemic area but with no clinical history of mala ria were positive by serology (8%) or by in vitro proliferation (21%). However, antibodies and cellular responses against rCS were detected only in malaria-exposed individuals, since those living outside the en demic area were all negative.