In this report we have shown that reovirus 1/L is an effective mucosal immunogen capable of generating a cytotoxic T cell (CTL) and associated helper T cell response to the nominal antigens associated with reovirus 1/L. The effectors that mediate reovirus-specific cytotoxicity are Thy-1+, Lyt-2+, and major histocompatibility complex (MHC)-restricted in their recognition of reovirus antigens, and can therefore be classified as CTLs. Frequency analysis of precursor CTLs occurring in Peyer's patches (PP) and peripheral lymph nodes (PLN) 6 d and 6 mo after intraduodenal stimulation have demonstrated that a persistent gradient of precursors is established, with higher frequencies present in PP. The generation of a CTL response in PP may be important in preferentially repopulating mucosal tissues with effector CTLs that could result in the local containment of infections in the gut. We also found that reovirus 1/L generates a virus-specific B cell response that is dominated by IgA memory cells after intraduodenal immunization. We hypothesize that the efficacy of reovirus 1/L at stimulating T and B cells in the gut mucosa is related to its ability to selectively enter PP via microfold (M) cells after enteric application. In this study we have also demonstrated that PP cells, upon in vitro culture and unrelated to prior reovirus priming, can generate natural killer-like (NK) cytotoxic activity. This may be an in vitro correlate of the in vivo generation of effectors that may populate mucosal tissues (i.e., the intestinal epithelium) with NK-like effector cells.

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