Ss Polymorphisms Carried on GPB in Brazilian Malaria Infected and Non-Infected Individuals.

Background: The present study was carried out to compare the Ss blood group polymorphisms carried on GPB in patients infected by malaria (n=51–100) with blood donors (n=100–170) living under the same conditions in a malaria endemic region of the Brazilian Amazon (Macapá, Belém, Porto Velho and Rio Branco). The blood donors had no clinical signs for malaria, their thick blood film exam was negative and they reported during the interview that they had no prior episodes of malaria.

Methods: Blood donors and individuals having only P. falciparum infected were identified and their blood was used for Ss phenotyping in gel cards (DiaMed-AG) and to prepare DNA for Ss genotyping and associations studies. The Ss polymorphisms were genotyped by allele-specific (AS)-PCR.

Results: Comparison between the frequencies of the Ss phenotypes/genotypes in the two studied groups in each endemic area showed a significant correlation between the frequency of individual carrying the S+s+ or S+s- phenotypes/genotypes and incidence of malaria infection in three regions of the study; Rio Branco, Porto Velho and Belem. The presence of the S antigen was significantly more frequent in malaria patients when compared with the blood donors in three regions of the study; Rio Branco (60.8 vs. 38%), Porto Velho (53.1 vs. 38%) and Belem (62 vs. 50%). As a confirmation, we also found that the S-s+ phenotype in the three regions was contributing to resistance to infection with malaria, as it was significantly more frequent in the donor population than in infected individuals. Importantly, there are approximately 1.5 times more copies of GPB in S+s- than in S-s+ RBCs. S+s+ RBCs have an intermediate amount of GPB. When we combined the results from the four regions and analyzed the 64 P. falciparum (Pf) positive individuals vs. the total 63 blood donors, 46 P. falciparum positive individuals (71.8%) carried the S+ phenotype on the GPB whereas in normal donor population only 30 individuals (47.6%) carried the S antigen.. In this analysis, the presence of the S antigen was significantly more frequent in the P. falciparum patients when compared with the blood donors (P = 0.006). Conversely, the S-s+ phenotype in the four regions was contributing to resistance to P. falciparum infection, as it was significantly more frequent in the donor population (52.3%) than in infected individuals (28.1%).

Conclusion: These results support the hypothesis that the expression of the S antigen on GPB is associated not only with incidence of malaria infection, but more importantly, with incidence of P. falciparum infection. These preliminary results open up the opportunity to study the utilization of the GPB invasion pathway, in particular via a domain that contains the S antigen, by the P. falciparum field isolates of Brazil.