Interestingly, although loss of CD11b+ DC in the subepithelial dome of the PP has been suggested to cause an incapacity to mount antigen-specific IgA responses in CCR6−/− mice,28 PP is the only GALT in CD47−/− mice that does not have a reduced frequency of this DC subset (before and after administration of CT). LGK-974 concentration In addition, in CD47−/− chimeric

mice reconstituted with WT BM, the frequency of DC is restored to WT levels in the spleen with a similar trend in the MLN. Despite this the capacity to generate OVA-specific intestinal IgA following oral immunization with OVA and CT is not regained. Therefore, the defect in OVA-specific IgA production is unlikely to be linked to the reduced frequency of CD11b+ DC, but is rather the result of the lack of CD47 expression by non-haematopoietic cells. In addition to defective activation of CD4+ T cells in INK 128 mw CD47−/− mice, another reason

for the reduced levels of OVA-specific intestinal IgA could be that IgA-secreting plasma cells generated in the PP do not properly home to the intestine in CD47−/− mice. This is consistent with the fact that the frequency of OVA-specific IgA-producing cells in the intestine is reduced in CD47−/− mice following immunization with OVA and CT. Entry of plasma cells into peripheral tissues requires extravasation across the blood endothelial wall. As endothelial cells express CD172a, it is possible that interactions between leucocyte CD47 and CD172a on vascular endothelial cells is important

for leucocyte transmigration, resulting in impaired ability of plasma cells generated in GALT to leave the circulation and efficiently home to the intestinal tissue in the absence of this bi-directional interaction. Obatoclax Mesylate (GX15-070) In addition, it has been shown that integrin-mediated phosphorylation of CD172a in endothelial cells is greatly reduced if the cells also lack CD47, which could have an impact on endothelial permeability.12 Hence, integrin-mediated transmigration could be hampered even if the leucocyte expresses CD47 if the endothelial cell still lacks this protein. This could possibly explain why reduced levels of anti-OVA-specific IgA are still generated in CD47−/− mice whose haematopoietic compartment is replaced with CD47-sufficient cells. This is also consistent with the normal levels of OVA-specific serum IgA and IgG in CD47−/− mice, as plasma cells secreting these immunoglobulins can reside in the BM without homing to the intestine. A third explanation for the reduced levels of intestinal anti-OVA IgA is the reduced number of cells in the intestinal tissue in CD47−/− mice. The reduction of cells in GALT was not due to one specific cell type.