Human immunodeficiency virus infection of CD4-bearing cells occurs by a pH-independent mechanism.

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Abstract
The effect of weak bases (NH4Cl and amantadine) and carboxylic ionophores (monensin) on the infection of CD4 (T4) positive human cell lines by HIV‐1 is examined. These reagents, which raise the pH of acidic intracellular organelles, fail to inhibit HIV‐1 entry and the events leading to viral protein synthesis at concentrations inhibitory for low pH‐dependent fusogenic enveloped viruses. The infectivity of VSV (HIV‐1) pseudotypes is unaffected by weak bases at concentrations causing 95% plaque reduction of VSV in its own envelope. HIV‐1 dependent cell–cell fusion (syncytium formation) occurs in medium maintained at pH 7.4‐7.6, and virions are not irreversibly inactivated by incubation in acid medium. Our results show that HIV‐1 entry and membrane fusion do not require exposure to low pH. The production of infectious HIV‐1 particles, however, is inhibited in cells treated with NH4Cl.