The aim of the present study was to investigate the inhibitory effect of synthetic peptides derived from the principle neutralizing domain of the V3 loop of the HIV-1 gp120 in the infectivity rates of HIV-1 variants with different tropism. Assessment of the viral infectivity was determined by detection of soluble HIV p24gag antigen in the culture supernatants of PM-1 T cells and primary macrophages after in vitro infection with the R5, Ba-L and X4, NL4.3 variants in the presence or absence of soluble V3-derived synthetic peptides. Our results showed a clear inhibition of Ba-L infectivity in both the PM-1 T cells and primary macrophages. The degree of inhibition was related to the number of basic amino acids in the peptide. The most effective inhibitory peptide, at a concentration of 50 ng/ml, was the one with the highest cationic potential, achieving over 60% inhibition to the PM-1 T cell line and over 90% to primary macrophages. The same peptides did not affect the NL4.3 infectivity. In addition to our previously reported observations on the electrostatic nature of the V3-CCR5 interaction, we show here that V3-like peptides from the more electropositive X4 variants may be useful as effective antagonists and potential infectivity blockers of the R5 variants.

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