IgG keeps virulent Salmonella from evading dendritic cell uptake
Article first published online: 1 JUN 2012
© 2012 The Authors. Immunology © 2012 Blackwell Publishing Ltd
Volume 136, Issue 3, pages 291–305, July 2012
How to Cite
Riquelme, S. A., Bueno, S. M. and Kalergis, A. M. (2012), IgG keeps virulent Salmonella from evading dendritic cell uptake. Immunology, 136: 291–305. doi: 10.1111/j.1365-2567.2012.03578.x
- Issue published online: 1 JUN 2012
- Article first published online: 1 JUN 2012
- Accepted manuscript online: 21 FEB 2012 01:46PM EST
- Received 30 June 2011; revised 16 January 2012; accepted 14 February 2012.
- dendritic cell;
- Fcγ receptors;
- Pathogenicity Island 1;
- Salmonella typhimurium
Dendritic cells (DCs) are phagocytic professional antigen-presenting cells that can prime naive T cells and initiate anti-bacterial immunity. However, several pathogenic bacteria have developed virulence mechanisms to impair DC function. For instance, Salmonella enterica serovar Typhimurium can prevent DCs from activating antigen-specific T cells. In addition, it has been described that the Salmonella Pathogenicity Island 1 (SPI-1), which promotes phagocytosis of bacteria in non-phagocytic cells, can suppress this process in DCs in a phosphatidylinositol 3-kinase (PI3K) -dependent manner. Both mechanisms allow Salmonella to evade host adaptive immunity. Recent studies have shown that IgG-opsonization of Salmonella can restore the capacity of DCs to present antigenic peptide–MHC complexes and prime T cells. Interestingly, T-cell activation requires Fcγ receptor III (FcγRIII) expression over the DC surface, suggesting that this receptor could counteract both antigen presentation and phagocytosis evasion by bacteria. We show that, despite IgG-coated Salmonella retaining its capacity to secrete anti-capture proteins, DCs are efficiently capable of engulfing a large number of IgG-coated bacteria. These results suggest that DCs employ another mechanism to engulf IgG-coated Salmonella, different from that used for free bacteria. In this context, we noted that DCs do not employ PI3K, actin cytoskeleton or dynamin to capture IgG-coated bacteria. Likewise, we observed that the capture is an FcγR-independent mechanism. Interestingly, these internalized bacteria were rapidly targeted for degradation within lysosomal compartments. Hence, our results suggest a novel mechanism in DCs that does not employ PI3K/actin cytoskeleton/dynamin/FcγRs to engulf IgG-coated Salmonella, is not affected by anti-capture SPI-1-derived effectors and enhances DC immunogenicity, bacterial degradation and antigen presentation.