Human T-cell lymphotropic virus type 1 Gag indeterminate Western blot patterns in Central Africa: Relationship to Plasmodium falciparum infection

To gain insight on the significance of human T-cell lymphotropic virus type I (HTLV-1) indeterminate serological reactivities, we studied villagers of South Cameroon, focusing on a frequent and specific HTLV-1 Gag indetermina te profile (HGIP) pattern (gag p19, p26, p28, and p30 without p24 or Env gp 21 and gp46), Among the 102 sera studied, 29 from all age groups had a stab le HGIP pattern over a period of 4 years. There was no epidemiological evid ence for sexual or vertical transmission of HGIP. Seventy-five percent of H GIP sera reacted positively on MT2 HTLV-1-infected cells by immunofluoresce nce assay. However, we could not isolate any HTLV-1 virus or detect the pre sence of p19 Gag protein in cultures of peripheral blood mononuclear cells obtained from individuals with strong HGIP reactivity. PCR experiments cond ucted with primers for HTLV-1 and HTLV-2 (HTLV-1/2 primers) encompassing di fferent regions of the virus did not yield HTLV-1/2 proviral sequences from individuals with HGIP, Using 11 peptides corresponding to HTLV-1 or HTLV-2 immunodominant B epitopes in an enzyme-linked immunosorbent assay, one epi tope corresponding to the Gag p19 carboxyl terminus was identified in 75% o f HGIP sera, while it was recognized by only 41% of confirmed HTLV-1-positi ve sera. A positive correlation between HTLV-1 optical density values and t iters of antibody to Plasmodium falciparum was also demonstrated. Finally, passage of sera through a P. falciparum-infected erythrocyte-coupled column was shown to specifically abrogate HGIP reactivity but not the HTLV-1 patt ern, suggesting the existence of cross-reactivity between HTLV-1 Gag protei ns and malaria-derived antigens, These data suggest that in Central Africa, this frequent and specific Western blot is not caused by HTLV-1 infection but could instead be associated with P. falciparum infection.