HHV-8 INFECTS AND REPLICATES IN PRIMARY CULTURES OF ACTIVATED B LYMPHOCYTES THROUGH DC-SIGN

Department of Infectious Diseases and Microbiology, Graduate School of Public Health; and Department of Pathology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15261

^* To whom correspondence should be addressed. Email: giovanna{at}pitt.edu.

	Abstract

Human herpesvirus 8 (HHV-8) is the etiological agent of Kaposi's sarcoma (KS), primary effusion lymphoma and some forms of multicentric Castleman's disease . Although latent HHV-8 DNA can be detected in B cells in persons with these cancers, there is little information on replication of HHV-8 in B cells. Indeed, B cells are relatively resistant to HHV-8 infection in vitro. We have recently shown that DC-SIGN, a C-type lectin first identified on dendritic cells (DC), is an entry receptor for HHV-8 on DC and macrophages. We have also demonstrated that B lymphocytes from peripheral blood and tonsils express DC-SIGN, and this expression increases after B cell activation. Here we show that activated blood and tonsillar B cells can be productively infected with HHV-8 as measured by an increase in viral DNA, the expression of viral lytic and latency proteins and the production of infectious virus. Infection of B cells by HHV-8 was blocked by pretreatment of the cells with antibody specific for DC-SIGN or mannan but not by antibody specific for xCT, a cystine/glutamate exchange transporter that has been implicated in HHV-8 fusion to cells. Infection of B cells with HHV-8 resulted in increased expression of DC-SIGN and a decrease in expression of CD20 and MHC class I. HHV-8 could also infect and replicate in B cell lines transduced to express full length DC-SIGN but not in B cell lines transduced with DC-SIGN lacking the transmembrane domain, demonstrating that entry of HHV-8 into B cells is related to DC-SIGN-mediated endocytosis. The role of endocytosis in viral entry was confirmed in activated B cells by blocking HHV-8 infection with endocytic pathway inhibitors Thus, expression of DC-SIGN is essential for productive HHV-8 infection and replication in B cells.