The role of inducible co-stimulator (ICOS)/B7-related protein-1 (B7RP-1) interaction in the functional development of Peyer's patches

T-cell co-stimulatory molecule, inducible co-stimulator (ICOS)/B7-related protein-1 (B7RP-1) interactions play an essential role of T-cell-dependent B-cell activation in peripheral lymphoid organs such as spleen and lymph nodes. Here, we investigate the role of ICOS/B7RP-1 interactions in the development of Peyer's patches (PPs). In ICOS^-/- mice, the number of PPs was not decreased, although PPs in ICOS^-/- mice were significantly reduced in size. Phenotypic analysis showed no obvious differences between ICOS^-/- and ICOS^+/- mice in the distribution of T-cells, B-cells, macrophages and dendritic cells. However, PNA⁺ cells characteristic of intestinal germinal centers were totally absent in ICOS^-/- mice. Moreover, production of IgA and IgG, but not IgM was significantly reduced in PPs in ICOS^-/- mice. These data suggest that ICOS/B7RP-1 interactions may not affect the organogenesis, but involve in the functional development of PPs.