Two populations of women with high and low spleen rates living in the same area of Madang, Papua New Guinea, demonstrate different immune responses to malaria.

Specific malaria and total IgM antibody responses were measured in 2 linguistically distinct coastal Papua New Guinean populations living in the same endemic malarious area, but exhibiting different adult female spleen rates (51% and 30%), in order to establish whether the higher spleen rates in the former group were due to hyper-reactive malarious splenomegaly (HMS). Malaria parasite rates were comparable, and geometric mean titres of IgG malaria antibody were the same, in both groups, indicating comparable exposure to malaria. A higher mean total IgM was observed in the high spleen (HS) rate group (6.07 g/litre, compared with 4.62 g/litre), a higher proportion was seropositive for IgM antibody to Plasmodium falciparum (63% compared with 54%), and HMS was found rather more frequently (4.7% compared with 2.6%). In both groups total IgM concentrations increased significantly with rising parity, and the mean level of 5.27 g/litre in young nulliparous women from the HS group suggested that IgM levels in this group at least were elevated from childhood. In both groups a rise in total IgM was associated with higher P. falciparum IgM geometric mean titres of antibody activity, a fall in parasite rates (HS group: 30% to 15%, P = 0.02; LS group: 24% to 0%, P = 0.034), and higher spleen rates (HS group: 38% to 65%, P = 0.001; LS group: 20% to 67%, P = 0.00012). It is concluded that the difference in spleen rates between the 2 groups was the result of differing degrees of acquired immunity to malaria, probably due to genetic differences in immune responses.(ABSTRACT TRUNCATED AT 250 WORDS)