Structural and functional differences between putative mucosal inductive sites of the rat.

Nasal-associated lymphoid tissue (NALT), bronchus-associated lymphoid tissue (BALT) and Peyer's patches (PP) were compared structurally and functionally using a model of local mucosal infection of rats with reovirus. Histological analyses showed that BALT lacks the typical lymphoid organization found in NALT and PP. After local reovirus infection, germinal centers developed in NALT with appearance of IgA+ cells, whereas no germinal centers or isotype-switched cells were found in BALT. Production of reovirus-specific IgA was observed in NALT and PP, but only small amounts of specific IgA were secreted by BALT. Both NALT and BALT showed considerable production of IgG2b, whereas this isotype was poorly produced by PP. These data reveal profound qualitative differences between these three mucosal sites, and strongly suggest that BALT is not a mucosal inductive site for reovirus-specific immune responses in the rat.