5 It is involved in regulating a range of functions including phagocytosis, cell adhesion and migration.6–8 CD47 was also found to be a receptor for the extracellular matrix protein thrombospondin,6 and to function as the ligand for signal regulatory protein α (SIRPα/CD172a).7,9 CD172a
is a cell surface immunoglobulin superfamily member expressed by most myeloid cells, but also by non-haematopoietic cells such as vascular endothelial cells selleck compound and smooth muscle cells.10,11 The cytoplasmic tail of CD172a contains immunoreceptor tyrosine-based inhibitory motifs that, upon phosphorylation, are able to recruit the tyrosine phosphatases SHP-1 or SHP-2. These phosphatases in turn modulate phagocytosis, cell migration and cellular responses to growth factors and other soluble signalling molecules.12 Not only interaction between CD47 and CD172a, but also integrin-mediated cell adhesion,10,11 leads to phosphorylation of the CD172a immunoreceptor tyrosine-based inhibitory motifs and regulation of these cellular functions. Blood monocytes, macrophages, granulocytes and Palbociclib cell line CD11b+ (CD4+) DC express CD172a.13,14 The expression of both CD47 and CD172a has recently been shown to be required for the homeostasis of CD11b+ DC in lymphoid organs,15 and also to regulate migration of this DC subset from skin to the draining
lymph nodes (LN).13,14,16 In intestinal tissues, CD172a–CD47 interactions are also required for the regulation of eosinophil degranulation and homeostasis.17 CD47 is crucial for cellular recruitment to sites of intestinal inflammation, as mice lacking CD47 (CD47−/−) fail to recruit CD172a+ CD11c+ cells to the gut and are therefore protected from trinitrobenzenesulphonic acid-induced colitis.18 Moreover, CD47 has been demonstrated to negatively regulate inducible Foxp3+ T regulatory cells expressing CD103, resulting in increased proliferation and accumulation of the T regulatory cells with age in CD47−/− mice.19 However, the role of CD47 in both the induction of immune responses following oral immunization with adjuvants and the maintenance of oral tolerance has not been investigated. In this study we use CD47−/− mice to
explore the role of CD47 and gut-associated lymphoid tissue (GALT) -resident CD172a+ antigen-presenting cells in the induction of oral tolerance and PAK5 following immunization with the adjuvant CT. We observe that CD47−/− mice exhibit reduced total cell numbers selectively in the GALT. In addition, we show that the frequency of CD11b+ CD172a+ DC is reduced by 50% in the small intestine and draining mesenteric lymph nodes (MLN) but not in the Peyer’s patches (PP). Although MLN are required for oral tolerance induction, CD47−/− mice maintain this capacity despite their diminished cell numbers. In contrast, production of antigen-specific intestinal IgA following oral immunization is significantly reduced in CD47−/− mice, although normal antigen-specific systemic IgG and total IgA levels are maintained.