Uptake of Particulate Antigens in a Nonmammalian Lung: Phenotypic and Functional Characterization of Avian Respiratory Phagocytes Using Bacterial or Viral Antigens

Abstract

Major distinctive features of avian lungs are the absence of draining lymph nodes and alveoli and alveolar macrophages (MPhs). However, a large network of MPhs and dendritic cells (DCs) is present in the mucosa of the larger airways and in the linings of the parabronchi. For the modulation of respiratory tract immune responses, for example, by vaccination, a better understanding of Ag uptake in the chicken respiratory tract is needed. In this study, we provide detailed characterization of APCs in chicken lungs, including their functional in vivo activities as measured by the uptake of fluorescently labeled 1-μm beads that are coated with either LPS or inactivated avian influenza A virus (IAV) mimicking the uptake of bacterial or viral Ag. We identified different subsets of MPhs and DCs in chicken lungs, based on the expression of CD11, activation markers, and DEC205. In vivo uptake of LPS- and IAV-beads resulted in an increased percentage MHC class II+ (MHC II+) cells and in the upregulation of CD40. The uptake of LPS-beads resulted in the upregulation of CD80 and MHC II on the cell surface, suggesting either uptake of LPS- and IAV-beads by different subsets of phagocytic cells or LPS-mediated differential activation. Differences in phagosomal acidification indicated that in chicken lungs the MHC II+ and CD80+ bead+ cell population includes DCs and that a large proportion of beads was taken up by MPhs. LPS-bead+ cells were present in BALT, suggesting local induction of immune responses. Collectively, we characterized the uptake of Ags by phagocytes in the respiratory tract of chickens.

Importance of Endosomal Cathelicidin Degradation To Enhance DNA-Induced Chicken Macrophage Activation

“…Nevertheless, the increased proinflammatory response toward DNA-CATH-2 complexes observed in this study was induced in both chicken and mouse macrophages, suggesting that, regardless of alternative downstream pathways for TLR9 and possibly TLR21, macrophages of both species appear to respond in a NFkB-dependent manner when presented with DNA-CATH-2 complexes. Further research will be needed to ascertain whether the different responses between cell types are due to differences in endosomal processing (37), downstream TLR signaling (38), or other processes.…”

Existence of Conventional Dendritic Cells in Gallus gallus Revealed by Comparative Gene Expression Profiling

“…In vivo, LCs have been identified in skin (20); in spleen and bursa, which is the primary B cell lymphoid organ in birds, CD83 + cells and CD205 + cells have been described, the later corresponding to both putative DCs and MPs (21,22). A subset of lung phagocytes presenting higher endosomal pH compared with resident MPs has also been identified in chicken (23). Although birds seem equipped with LCs and can develop DC-type cells from bone marrow ex vivo, it is not known whether they dispose of the cDC lineage homologous to that of mammals (23).…”

“…A subset of lung phagocytes presenting higher endosomal pH compared with resident MPs has also been identified in chicken (23). Although birds seem equipped with LCs and can develop DC-type cells from bone marrow ex vivo, it is not known whether they dispose of the cDC lineage homologous to that of mammals (23). In addition, whether the biological differences between cDCs and MPs recently unraveled in mammals pertain to distant vertebrate species such as birds is not known.…”

Induction of respiratory immune responses in the chicken; implications for development of mucosal avian influenza virus vaccines

“…In chicken, BALT is constitutively present and is thought to compensate for the lack of dLN. When chickens were inoculated with fluorescent beads that were coated with LPS as a bacterial Ag, bead þ cells were present in BALT areas (de Geus, Jansen, et al 2012). This could indicate that following the uptake of Ag, APC migrate mainly locally towards the BALT area.…”

“…MPh have much higher levels of proteolysis than DC, which limits their efficiency as APC (Delamarre et al 2005). Recently, lung phagocytic cells were identified in chicken that decreased the pH of their endosomal compartment following the uptake of a bead (CD11 þ , KUL01þ and CD40þ phagocytes) and cells that did not (MHC IIþ and CD80þ phagocytes) (de Geus, Jansen, et al 2012), suggesting that in chicken MPh also are functionally distinct from DC. Whether the capacity to present antigen differs between these cell populations needs further investigation.…”