Characterization of the Placental Macrophage Secretome: Implications for Antiviral Activity

It is well documented that placental macrophages show lower levels of HIV-1 infection than monocyte-derived macrophages (MDM). We used proteomic methods to test the hypothesis that placental macrophages secrete different proteins as compared to MDM that may contribute to decreased HIV-1 replication. Placental macrophages and MDM were cultured for 12 days and supernatant was collected. To characterize supernatants, the protein profiles of placental macrophages and MDM were compared using the protein chip assay. Subsequently, proteins were separated by one-dimensional gel electrophoresis and identified by tandem mass spectrometry at the corresponding mass to charge (m/z) range of 5000-20,000. Significant differences were found between placental macrophages and MDM in seven protein peaks with m/z values of 6075, 6227, 11,662, 14,547, 6158, 7740, and 11,934 on the CM10 and IMAC chips. After sequencing and identification, five proteins were validated for differential expression in placental macrophages and MDM by Western blot analyses. Peroxiredoxin 5, found to be more abundant in placental macrophage supernatants, is important in the cellular antioxidant mechanisms, and other members of its family have shown antiviral activity. Cystatin B was less abundant in PM supernatant, and decreased intracellular levels have recently been shown to be associated with lower HIV-1 replication in placental macrophages than in MDM. This study elucidates for the first time the placental macrophage secretome corresponding to 5000-20,000 Da and advances our understanding of the proteins secreted in the placenta that can protect the fetus against HIV-1 and other viral infections.