Effects of cholera toxin on delayed-type hypersensitivity to sheep red blood cells inoculated intranasally into mice.

The effects of cholera toxin (CT) on delayed-type hypersensitivity (DTH) to sheep red blood cells (SRBC) were studied in mice sensitized by intranasal administration of SRBC. CT (1 microgram/mouse), given intranasally together with SRBC (2 x 10(7)/mouse), induced a maximally enhanced DTH response, which reached its peak around 7 days after sensitization, and also induced an accelerated DTH response upon a second administration of SRBC 28 days later. The ability of CT to enhance the DTH to SRBC was lost, either when CT was administered via the intraperitoneal or subcutaneous route, or when CT was introduced into the nasal site from which a large proportion of the SRBC was discharged 2 days after SRBC administration. These results indicate that the cells that are located in the nasal site and participate in the earlier events of DTH response were most affected by CT. The following effects of CT on the earlier events, which occur within 24 hr after the intranasal administration of both CT and SRBC, appeared to be involved in the mechanisms by which CT enhances DTH to SRBC: (i) facilitation of the penetration of the antigen into the nasal tissue; (ii) reinforcement of the migration of immunocompetent cells from the blood to the nasal tissues; (iii) promotion of the ability of Ia-positive macrophages to present the antigenic determinants to T cells; (iv) facilitation of the differentiation of primed T cells to DTH-effector T cells.