Human IgG subclass antibodies to the 19 kilodalton carboxy terminal fragment of Plasmodium falciparum merozoite surface protein 1 (MSP119) and predominance of the MAD20 allelic type of MSP1 in Uganda

Objective: To determine the natural human humoral immune responses to the 19 kilodalton carboxy terminal fragment of Plasmodium falciparum merozoite surface protein 1 (MSP1(19)), a malaria candidate vaccine antigen and to determine the prevalence of MAD20 and K1 alleles of P. falciparum MSP1, Design: Community based cross-sectional study. Setting: Atopi Parish, Apac District, Uganda, 1995, Subjects: Three hundred and seventy four Ugandans between <1 and 70 years old provided serum samples. Main outcome measures: IgG subclass antibodies by ELISA; MAD20 and K1 allelic types of MSP1 by PCR, Results: Both the prevalence and the mean concentration of serum IgG1, and to a lesser extent IgG3, antibodies increased with age. IgG2 or 1gG4 antibodies were virtually nonexistent. The cross-reactivity between the 4 sequence variants (E-KNG, E-TSR, Q-KNG and Q-TSR) of MSP1(19) was confirmed; however, a minority of sera preferentially recognised the KNG but not the TSR variants. All 33 P,falciparum isolates from different parts of m Uganda carried the E-TSR (Mad20) allelic type and 3 isolates were mixed infections with E-TSR (MAD20) and Q-KNG (K1) allelic types, confirming the rarity of the K1 allele in Uganda, Conclusion: There is a robust IgG1 antibody response to the malaria vaccine candidate antigen MSP119 which begins at an early age. Future cohort studies are necessary to estblish the impact of these antibodies on clinical immunity to malaria. The MAD20 allelic type of MSP1 id predominant in Ugandan P, falciparum isolates.