KSHV activates the HGF/c-MET pathway in vitro and in vivo. (A) Four KSHV⁺ PEL cell lines were incubated with a monoclonal antibody recognizing the extracellular domain of c-MET (black line) or isotype antibody as a negative control (gray line), followed by a secondary antibody conjugated to Alexa 647. Surface expression of c-MET was quantified using flow cytometry. (B-C) HUVECs were infected by purified KSHV (MOI = 10), and the supernatant and cell lysates were collected at indicated time points. HGF concentrations in supernatant were determined by ELISA and protein expression was measured by immunoblots. Error bars represent the S.E.M. for 3 independent experiments. *P < .01. (D) The HGF concentrations in plasma from cohort HIV-infected patients were determined by ELISA, and KSHV infection status was determined by using ELISAs for identifying circulating IgG antibodies to KSHV proteins as described in “Methods.” S.E.M., standard error of the mean.