CD4-independent binding of HIV-1 to the B lymphocyte receptor CR2 (CD21) in the presence of complement and antibody.
Complement and antibody contribute to infection-enhancement and possible expanded cellular tropism of HIV-1 in vitro through a process requiring complement receptors. Until now, however, the ability of HIV-1 to bind complement receptors has not been documented or characterized. We investigated whether antibody and complement permitted HIV-1 to bind to the B lymphocyte receptor, CR2 (CD21), in an effort to learn more about infection-enhancement, and also because CR2 can mediate B cell proliferation and antigen localization in lymphoid organs in other systems. HIV-1 incubated with antibody and fresh human serum as a source of complement bound approximately 10-fold greater to cells expressing CR2 than to HIV-1-permissive cells lacking this receptor. A similar effect was observed using cells which expressed CR2 but no CD4. This binding was minimal in heat-inactivated and C3-deficient sera, and was significantly reduced by the anti-CR2 MoAb, OKB7, but not by the anti-CD4 MoAb, OKT4a. Thus, complement and antibody acted in concert to facilitate the binding of HIV-1 to CR2 independently of CD4. CD4-independent binding of HIV-1 to CR2 was not sufficient to produce infection in Raji-3 cells. Titres of antibodies mediating CR2 binding correlated with antibody titres as measured by immunofluorescence (P < 0.01) and infection-enhancement (P < 0.05) but were discordant with titres of neutralizing antibodies, a result consistent with the utilization of CR2 for enhanced infection of cells. The ability of complement and antibody to facilitate the binding of HIV-1 to CR2 in the absence of CD4 provides new insights into mechanisms of HIV-1-induced immunopathogenesis and infection-enhancement.
Department of Pathology, Vanderbilt University Medical School, Nashville, TN 37232.
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Montefiori
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Zhou
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Shaff
D000906:Antibodies / Q000494:pharmacology*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000378:metabolism*; D002051:Burkitt Lymphoma; D018801:CD2 Antigens; D003165:Complement System Proteins / Q000494:pharmacology*; D015497:HIV-1 / Q000378:metabolism; D006801:Humans; D015728:Receptors, HIV / Q000378:metabolism*; D011971:Receptors, Immunologic / Q000378:metabolism*; D011991:Receptors, Virus / Q000502:physiology; D014407:Tumor Cells, Cultured / Q000382:microbiology
D000906:Antibodies; D000945:Antigens, Differentiation, T-Lymphocyte; D018801:CD2 Antigens; D015728:Receptors, HIV; D011971:Receptors, Immunologic; D011991:Receptors, Virus; D003165:Complement System Proteins