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Background:  Divergent findings have been reported on the susceptibility of dendritic cells (DC) to infection by HIV. This might reflect the heterogeneity of DC populations regarding the maturation state and HIV receptors and co-receptors. Another factor that might contribute to these divergent results is a differential expression of the cytidine deaminase APOBEC3G (Apo3G), which prevents HIV infectivity, a protective effect that is eliminated by the viral protein Vif. The expression of  Apo3G by the different DC populations remains unknown and this study was aimed to gain insight on this issue.

Methods:  To quantify levels of  Apo3G mRNA transcription, a RT-PCR was developed using primers that amplify a 278-bp product encompassing part of second and third exons. Two mouse monoclonal antibodies to Apo3G were generated using Apo3G-GST fusion protein as the immunogen. Immature and cytokine-matured monocyte-derived DC (MDDC) and highly purified blood plasmocytoid and myeloid DC from healthy individuals were studied. Normal monocytes and resting and activated T lymphocytes, as well as the permissive T-cell lines SupT1 and CEM-SS T-cell lines were also analyzed.

Results:  The levels of Apo3G mRNA in normal T cells were high and nearly undetectable in SupT1 and CEM-SS; no differences were found between in vitro-activated and resting normal T lymphocytes. The levels of Apo3G mRNA in monocytes were clearly lower than in T cells and the same occurred with immature MDDC. Maturation of  MDDC with the IL-1⁺IL-6⁺TNF-γ PGE2 cocktail caused a clear up-regulation of Apo3G mRNA expression, which was also reflected in the levels of protein as assessed by Western blotting with the anti-Apo3G monoclonal antibody. This differential expression of Apo3G in immature and mature MDDC was confirmed in 4 different experiments with cells from different subjects. Importantly, no Apo3G mRNA was detected in either plasmocytoid DC or myeloid DC, a finding confirmed in 3 different individuals.

Conclusions:  We have developed anti-Apo3G mouse monoclonal antibodies that can be used to assess Apo3G protein expression in cells. The reduced expression of Apo3g in immature MDDC compared with cytokine-matured MDDC is compatible with data on the higher vulnerability of immature MDDC to HIV infection than cytokine-matured MDDC. The absence of Apo3G expression in blood plasmocytoid DC and myeloid DC is also consistent with recent data demonstrating the in vitro and in vivo infectivity by HIV-1 of  both types of circulating DC.

Keywords: Dendritic cells; APOBEC3G; anti-APOBEC3G monoclonal antibody