Objectives:We examined the effect and time of addition of &bgr;-chemokines on human immunodeficiency virus type 1 (HIV-1) replication, binding, and uncoating in human macrophages and measured CCR5 receptor expression during virus binding and uncoating.Methods:Macrophages were treated with &bgr;-chemokines before infection, at infection, or postinfection, and virus replication was determined by p24 antigen level. Binding and uncoating of35[S]-methionine-labeled HIV-1 was measured. CCR5 expression was determined by flow cytometry.Results:The &bgr;-chemokines potently inhibited virus replication. The strongest inhibition occurred when cultures were pretreated and maintained with &bgr;-chemokines. &bgr;-Chemokines also caused strong inhibition of viral uncoating and a considerable decrease in CCR5 expression during uncoating.Conclusions:CCR5 receptors appear to be internalized and recycled to the cell surfaces during HIV entry. The downregulation of CCR5 expression by &bgr;-chemokines during virus uncoating probably accounts for the reduction in virus uncoating (entry) and hence in virus replication.Journal of Human Virology 1999;2:123-132 © Lippincott Williams & Wilkins, Inc.