IFN-γ and IL-6 induce an increase in fusion of MDM with T-tropic envelopes in the absence of an increase in CXCR4 surface expression.

(A) MDMs untreated or treated with cytokines were cocultured with IIIB-envelope–expressing cells (TF228). Syncytia were scored after 18 hours. Aliquots of MDMs used for the fusion assay were stained with anti-CXCR4 (12G5) (B) and with anti-CD4 monoclonal antibodies (C). The ΔMFCs were calculated by subtracting the isotope control MFC from the experimental values. Results from 12 separate experiments are presented.