Frequency of human leukocyte antigen (HLA) in patients with malaria and in the general population of Humaitá County, Amazonas State, Brazil.

In August 1983,85 inhabitants o f the municipality o fHumaitá, Amazonas State, Brazil were studied to determine the prevalence o f antigens to HLA-A, -B, -C and DR. Thirty-eight were sick with malaria due to Plasmodium falciparum. All subjects were examined for splenomegaly, blood parasitaemia and antibodies to malaria. They constituted three groups: 1) 25 subjects native to the Amazon region who had never had malaria; 2) 38 Amazonian subjects who had malaria in the past or currently had an infection; 3) 22 patients with malaria who had acquired the infection in the Amazon Region but came from other regions o f Brazil. Blood was taken from each person, the lymphocytes were separated and typed by the test o f microlymphocytotoxicity. There was a high frequency o f antigens that could not be identified in the groups studied which suggests the existence o f a homozygote or phenotype not identified in the population. There was a high frequency o f the phenotype Ag(W24) (44.7%) in group 2 when compared with group 1 (32%) or group 3 (9%). Also the individuals in group 2 showed an elevated frequency o f antigen DR^80% ) when compared with group 1 (36.6%) or group 3 (16.6%). These observations suggest the possibility o f a genetic susceptibility to malaria among Amazonian residents and indicate a necessity for more extensive studies o f the frequency o f HLA antigens among inhabitants of this endemic malarial zone.