Spreading infection assay. Replication of R5 (A) and X4 (B) virus in TN, TCM and TEM cells after DC-mediated HIV-1 transmission. Alternatively, the T cell subsets were stimulated by crosslinking CD3/CD28 with antibodies and infected with R5 (C) or X4 (D) virus. Viral replication was followed by CA-p24 ELISA on the supernatant. Error bars represent standard deviations.