CD16+ CD32+ monocytes are key effector cells in antibody-dependent cellular cytotoxicity mediated by anti-HIV-1 Env antibodies in the RFADCC assay
S. Al Darmaki, R. Flinko, Y. Guan, R. Kamin-Lewis, G.K. Lewis
Institute of Human Virology of the University of Maryland School of Medicine, Division of Basic Science and Vaccine Research, Baltimore, United States
Background: ADCC has been associated with decreased viral load and elevated CD4+ T cells in AIDS patient. In addition, vaccine elicited antibodies that mediated ADCC correlated with significant reduced viral load in rhesus macaques and declined level of SIV-infected cells. Unlike CTL activity ADCC is non-MHC restricted response that is applicable to all HIV infected humans. The purpose of the current study is to determine the relative contributions of human monocytes and NK cells into ADCC mediated by anti-HIV-1 Env antibodies in the rapid fluorometric ADCC assay (RFADCC).
Methods: ADCC mediated by human monocytes and NK cells armed with anti-HIV-1 Env antibodies was measured by RFADCC. Briefly, CEM target cells are double stained with PKH-26 and CFSE and coated with gp120 from the HIV-1Ba-L isolate. The gp120-coated CEM cells are incubated with ani-HIV-1 Env mabs, cultured with purified human NK or Monocytes, and killing assessed by dye loss using flow cytometry.
Results: NK cells and Monocytes differentially contributed into ADCC mediated by anti-HIV Env antibodies. Monocytes efficiently mediated ADCC while NK cells were substantially less active. Interestingly, monocyte-mediated ADCC is critically dependent on the engagement of FCγRIII (CD16) and FCγRII (CD32), suggesting the involvement of stimulatory and inhibitory Fc-receptors in this response.
Conclusions: Our results suggest that monocytes are key effector cells in ADCC mediated by anti-Env mabs that is detected by the RFADCC assay. Previous studies indicated that both activator (CD16) and inhibitory (CD32) FCγRs are required for the regulation of ADCC activity in vivo. Our studies indicate that these receptors also play a role in vitro in the monocyte-mediated component of the RFADCC assay. As ADCC is an early and rapid response against HIV-1 infection that might be particularly important in antibody-mediated protection against transmission, our studies suggest that CD16+ CD32+ monocytes should be considered as potential effector cells in this setting.
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