Definition of the range and distribution of human immunodeficiency virus macrophage tropism using PCR-based infectivity measurements

Abstract

The tropism of human immunodeficiency virus (HIV) for macrophages (mφ) is a well recognized phenomenon, but the range and distribution of mφ-tropic phenotypes have not been defined by quantitative means. This study uses a PCR-based infectivity assay to derive an index of mφ tropism for several common strains of HIV. The results show that mφ tropism varies over about six orders of magnitude and that the most mφ-tropic strains have a higher infectivity for mφ than for peripheral blood lymphocytes. Strains were distributed throughout this range, suggesting that mφ tropism is a continuously variable phenotypic property. Although the degree of tropism was strongly influenced by the mode of isolation and propagation of virus strains, there was no evidence for the existence of distinct mφ-tropic or non-mφ-tropic phenotypes. Finally, the tropism of two selected strains was found to be determined by an early step in replication, probably virus entry.