Background: Chemokines have received increasing attention due to their inhibitory activities on human immunodeficiency virus type-I (HIV-1) and simian immunodeficiency virus (SIV) replication, and the potential for chemokine receptors to assist in HIV-1/SIV entry into permissive cells.  Besides CD4, which is the major receptor for HIV-1 and SIV, a number of chemokine receptors including but not limited to APJ, CCR3, CXCR4, and CCR5 may be co-receptors for HIV-1/SIV, not only in peripheral blood and lymphoid tissues but also in the central nervous system (CNS). The blood-brain barrier mainly constituted of MVECs is the first line of defense protecting the brain from invasion of infection. This necessitates discerning the presence and role of various receptors involved in HIV-1 entry via MVECs

Methods: Immunocytochemical analyses were utilized to confirm the presence of specific chemokine receptors and C-type lectins on primary brain MVECs. Immunocytochemical findings were further substantiated by reverse transcriptase polymerase reaction (RT-PCR). Viral attachment on primary brain MVECs and inhibitory potential of various chemokine inhibitors was determined by HIV-1 p24 antigen binding assays.

Results: The present studies reveal the lack of CD4, but the significant expression of various chemokine receptors, APJ, CCR3, CXCR4, and CCR5 plus C-type lectins DC-SIGN and L-SIGN on isolated primary human brain MVECs. As these MVECs do not express CD4, this suggests a CD4-independent HIV/SIV entry/infection of these cells, which are the major cells constituting the human blood-brain barrier (BBB). We also found that chemokines for cognate chemokine receptors were unable to block binding of HIV-1 to brain MVECs.

Conclusions: These results reveal that in primary isolated brain, MVECs viral attachment is mediated by a possible previously unknown receptor(s) or by cooperative activity of various receptors. Moreover, mRNA transcripts for DC-SIGN/L-SIGN, as well as DC-SIGN protein expression, suggest the capability of MVECs to attach viral particles on cell surfaces, even though polyclonal antisera for DC-SIGN did not affect viral binding to these cells. These data will assist in further understanding the molecular mechanisms of lentiviral entry into the CNS.