IMMUNE-RESPONSE AGAINST THE EXP-1 PROTEIN OF PLASMODIUM-FALCIPARUM RESULTS IN ANTIBODIES THAT CROSS-REACT WITH HUMAN T-CELL LYMPHOTROPIC VIRUS TYPE-1 PROTEINS

To examine the role of the Plasmodium falciparum Exp-l blood-stage pro tein in producing antibodies that cross-react with human T-cell lympho tropic virus type I (HTLV-I) proteins, we studied sera from Indonesian volunteers who seroconverted to malaria after transmigrating to an ar ea where malaria is hyperendemic, Samples from Philippine volunteers, that were used in a prior study that examined malaria antibodies that cross-react with HTLV-I proteins, were also used. Eighty-three percent of the Indonesian transmigrants developed antibodies against the mala ria Exp-l protein by 6 months postmigration. Of these malaria seroconv erters, 27% developed false-positive HTLV-I enzyme immunoassay (EIA) i mmunoreactivity, as indicated by indeterminate HTLV-I Western blot ban ding patterns. Five of the six Philippine samples tested were HTLV-I E IA false positive and Western blot indeterminate. When a recombinant E xp-l protein was used in blocking experiments, the HTLV-I Western blot immunoreactivity of sera from both groups was either completely elimi nated or greatly reduced. No effect on the Western blot immunoreactivi ty of truly HTLV-I-positive sera was seen, To determine if immunizatio n with the recombinant Exp-1 protein could elicit the production of HT LV-I antibodies, six mice were inoculated with the recombinant protein . Following administration of three 50-mu g doses of the protein, four of the six mice developed antibodies that cross-reacted with HTLV-I p roteins on Western blot. These results indicate that the immune respon se against the malaria Exp-l protein may result in HTLV-I-cross-reacti ng antibodies that can lead to false-positive EIA and indeterminant We stern blotting results.