These results show that CD47−/− mice have a reduced ability to generate antigen-specific intestinal IgA following oral immunization. However, this does not reflect a general defect in antibody production, as CD47−/− mice exhibit normal levels of total intestinal IgA and a maintained capacity to generate antigen-specific serum IgG and IgA following oral immunizations. To determine if expression of CD47 by haematopoietic cells was sufficient to NVP-BEZ235 restore cellularity in GALT, the frequency of CD11b+ DC and the capacity to generate OVA-specific intestinal IgA following immunization, we irradiated CD47−/− mice and introduced WT BM to generate WT/CD47 chimeras. Irradiation controls (CD47/CD47 and WT/WT) were also generated
but not CD47/WT, as WT macrophages would phagocytose the CD47-deficient BM cells after transfer.25 Oral immunization with CT influenced neither the total number of cells in GALT nor the frequency of CD11b+ DC 2 weeks after immunization, as no significant differences in either parameter were observed when comparing unimmunized WT mice and mice fed CT three times (data not shown). The three groups of chimeric mice were immunized with OVA and CT three times then the level of OVA-specific intestinal IgA, the cellularity in GALT and the frequency of CD11b+ DC were assessed. Intestinal anti-OVA IgA titres and the total number of cells in the MLN of WT/CD47 XL765 order mice were significantly
lower than in WT/WT mice, but not significantly different from CD47/CD47 mice (Fig. 5a and b). In contrast, the frequency of CD11b+ DC in the spleen of WT/CD47 reached Resminostat the same level as in WT/WT mice and was significantly higher than in CD47/CD47 mice (Fig. 5c). When the frequency of CD11b+ cells among MHC-IIbright DC in the MLN was determined, although the trend was the same as in the spleen, the individual variance between the mice was too large to obtain a significant difference between the groups (Fig. 5d). These results show that the expression of CD47 on non-haematopoietic cells is required
for normal cellularity in GALT and for the generation of OVA-specific intestinal IgA after oral immunizations. Intestinal antigen-presenting cells, in particular DC, are key cells for the induction of oral tolerance as well as for generation of protective IgA antibodies secreted into the lumen of the gut.3,4 CD4+ T cells are required in these processes, and recent results suggest that regulatory T cells also play an important role.26 Previous studies have shown that mice lacking CD47 have reduced numbers of CD11b+ DC, an accumulation of regulatory T cells with age, and reduced susceptibility to induced colitis.13,14,18,19 In this study we show that oral immunizations of CD47−/− mice with OVA and CT result in a significantly reduced intestinal anti-OVA IgA response compared with WT mice. It has been shown that PP, and not MLN or isolated lymphoid follicles, are the major site for generation of specific IgA following oral immunization with CT.