We have examined cytotoxic responses of lymphocytes derived from the gut epithelium of mice primed systemically and enterically with alloantigens. Both gut intraepithelial (IEL) and splenic lymphocytes from alloantigen-primed mice were found to contain antigen-specific cytotoxic T cell activity. However, after priming, gut IEL also developed high levels of natural killer and spontaneous cytotoxic cell activities. We suggest that this nonspecific activation of additional cytotoxic effector populations during an antigen-specific response is an important host immune defense within the intestinal mucosa.

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