Besides interactions between the viral envelope glycoproteins with cell surface receptors, interactions between cell-derived molecules incorporated onto virions and their ligand could also modulate HIV type-1 (HIV-1) entry inside CD4(+) T lymphocytes. Although incorporation of host ICAM-1 within HIV-1 increases both virus attachment and fusion, the precise mechanism through which this phenomenon is occurring is still unclear. We demonstrate in this study that activation of primary human CD4(+) T lymphocytes increases LFA-1 affinity and avidity states, two events promoting the early events of the HIV-1 replication cycle through interactions between virus-embedded host ICAM-1 and LFA-1 clusters. Confocal analyses suggest that HIV-1 is concentrated in microdomains rich in LFA-1 clusters that also contain CD4 and CXCR4 molecules. Experiments performed with specific inhibitors revealed that entry of HIV-1 in activated CD4(+) T cells is regulated by LFA-1-dependent ZAP70, phospholipase Cgamma1, and calpain enzymatic activities. By using laboratory and clinical strains of HIV-1 produced in primary human cells, we demonstrate the importance of the LFA-1 activation state and cluster formation in the initial step of the virus life cycle. Overall, these data provide new insights into the complex molecular events involved in HIV-1 binding and entry.