Human T-cell lymphotropic virus type 1 gag indeterminate western blot patterns in Central Africa: relationship to Plasmodium falciparum infection

Abstract

To gain insight on the significance of human T-cell lymphotropic virus type 1 (HTLV-1) indeterminate serological reactivities, we studied villagers of South Cameroon, focusing on a frequent and specific HTLV-1 Gag indeterminate profile (HGIP) pattern (gag p19, p26, p28, and p30 without p24 or Env gp21 and gp46). Among the 102 sera studied, 29 from all age groups had a stable HGIP pattern over a period of 4 years. There was no epidemiological evidence for sexual or vertical transmission of HGIP. Seventy-five percent of HGIP sera reacted positively on MT2 HTLV-1-infected cells by immunofluorescence assay. However, we could not isolate any HTLV-1 virus or detect the presence of p19 Gag protein in cultures of peripheral blood mononuclear cells obtained from individuals with strong HGIP reactivity. PCR experiments conducted with primers for HTLV-1 and HTLV-2 (HTLV-1/2 primers) encompassing different 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 epitope corresponding to the Gag p19 carboxyl terminus was identified in 75% of HGIP sera, while it was recognized by only 41% of confirmed HTLV-1-positive sera. A positive correlation between HTLV-1 optical density values and titers 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 pattern, suggesting the existence of cross-reactivity between HTLV-1 Gag proteins 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.

FIG. 1

WB (HTLV2-3; Diagnostic Biotechnology) which contains disrupted HTLV-1 virions, a recombinant gp21 (rg21) protein, as well as MTA-1 (amino acids 169 to 209) and K55 (amino acids 162 to 205) which are gp46 HTLV Env-specific peptide of HTLV-1 and HTLV-2, respectively, were used. Representative WB obtained with sera from individuals infected with HTLV-1 (lane 1) or HTLV-2 (lane 2) or exhibiting an HGIP WB pattern (lane 3).

FIG. 2

Indirect IFA with (A) an HTLV-1 serum, (B) an HGIP serum, and (C) a control serum. MT-2 (HTLV-1 producing) and CEM (negative control) cells were split and acetone fixed at a ratio of 1:4. The serum is used at a 1:40 dilution. Results are representative of at least five independent experiments.

FIG. 3

Immune responsiveness to 11 immunodominant epitopes from the Gag, Pol, Env, Tax, and Rex proteins of HTLV-1 or HTLV-2 in patients with (A) HTLV-1 (n = 12), (B) HTLV-2 (n = 11), and (C) HGIP (n = 26) WB profiles. As controls, 18 HTLV-1/2-negative sera from the same area of Cameroon were used. Results are expressed as percent of sera above the cut off value determined as the mean absorbancy obtained with 18 HTLV—seronegative controls obtained from the same Cameroonian region plus three standard deviations. These results are representative of two independent experiments.

FIG. 4

Competitive inhibition of HTLV-1 or HGIP antibodies with a Sepharose column loaded with P. falciparum-infected or noninfected erythrocytes. Lanes 1 and 6, HTLV-1 serum from Cameroon; lane 2, same serum after incubation with a Sepharose column loaded with P. falciparum-infected erythrocytes; lane 3, reactivity of the eluted antibodies; lane 4, same serum after incubation with a Sepharose column loaded with noninfected erythrocytes; lane 5, reactivity of the eluted antibodies; lane 7, HGIP serum from Cameroon; lane 8, same serum after incubation with a Sepharose column loaded with P. falciparum-infected erythrocytes; lane 9, reactivity of the eluted antibodies; lane l0, same serum after incubation with a Sepharose column loaded with noninfected erythrocytes; lane 11, reactivity of the eluted antibodies. This result is representative of three independent experiments.