Demonstrating the relevance of findings using HEK293 cell systems, infection of CHME3 4×4 (a human microglia line which expresses higher levels of CD4 and CXCR4 for more efficient infection with wildtype HIV-1 envelope)16,22 or primary human monocyte-derived macrophages (MDMs) with either X4-tropic pNL4.3 or R5-tropic JR-CSF resulted in a similar decrease in both full-length APP and its CTFs (Fig. 1c, d, respectively). This evidence concerns the gene CXCR4 and infection.