The HLA analysis program deduces the HLA-DRB1 and HLA-DQB1 allelic groups. Analyses were done using Epi Info 2007 (CDC, Atlanta, GA), Instat or Prism

5 (GraphPad Software, San Diego, CA). Differences in medians for the study population data were tested by non-parametric Mann–Whitney test where appropriate. Student’s t test was used to compare means of normally distributed data, and normalized transformations were performed on raw data before testing by one-way analysis of variance where appropriate. Differences in proportions were evaluated by Chi-square (χ2) test. Relationships between years of residence in the endemic area and number of past malaria infections or months since last known malaria episode were assessed with Spearman’s rank correlation. Bipartition χ2 was used to evaluate the relationship between HLA-DRB1 and the frequency of cellular immune response. HLA-DRB1 and -DQB1 alleles were also analyzed GSK1210151A molecular weight for association with the IFN-γ or IL-4 response to PvMSP9 peptides, and when appropriate a relative risk was calculated. The epidemiological and demographic data of the studied population have been described previously [14]. Briefly, the majority of the volunteers are natives of the Amazon forest or residents living in the state of Rondonia for approximately 20 years and transmigrants from non-endemic regions who have lived in malaria endemic regions for at least 10 years. All individuals

were exposed MDV3100 research buy to P. vivax and P. falciparum infections throughout

the year. At the time of the blood collection the frequency of malaria infected individuals was very low, 11 individuals were infected with P. vivax and 4 with P. falciparum. However, the majority of our donors confirmed a prior history of malaria infections. Five out of the 11 synthetic peptides tested, predicted to be promiscuous, showed that the overall frequencies of IFN-γ and IL-4 responders to at least one of the peptides were 61.2% and 49%, respectively. The frequency of IFN-γ responders was significantly higher than IL-4 for peptides pE (p = 0.0006), pK (p = 0.0462) and pL (p = 0.0015), but no difference was observed for peptides pH and pJ. When the pattern of the responses was examined, significant differences were observed, very and the frequencies of positive responses induced by different peptides varied. In evaluating the IFN-γ responses, the peptides pE and pL were more commonly recognized than pH, pJ and pK (p < 0.05). For IL-4 responses, no differences were observed among the synthetic peptides tested ( Fig. 1). The mean numbers of adjusted IFN-γ-SFC elicited by all tested peptides (pE = 43 ± 23; pH = 39 ± 14; pJ = 38 ± 19; pK = 41 ± 21; pL = 43 ± 21) were significantly higher than IL-4-SFC (pE = 21 ± 8; pH = 25 ± 11; pJ = 23 ± 8; pK = 21 ± 9; pL = 22 ± 10). A Venn diagram organizes the relationships among the cellular responses to overlapping peptides pH, pK and pL ( Fig. 2).