Humoral and cell-mediated immune responses in chronic typhoid carriers.

Humoral and cell-mediated immune responses to Salmonella typhi were studied in 10 chronic typhoid carriers, and in healthy controls. Carriers showed impaired cellular reactivity to S. typhi antigens in the leucocyte migration inhibition test (LMI). Carriers did not show a generalized depression of cell-mediated immunity in that delayed hypersensitivity skin test responses to recall antigens, peripheral blood T cell numbers, and lymphocyte transformation responses to mitogens were normal. Lymphocyte transformation in the presence of S. typhi antigen occurred to a greater extent than normal in four of six subjects tested and suggested the possibility of dissociated defects of cellular immunity. Carriers showed normal humoral immunity, as judged by antibodies to the flagellar and somatic antigens of S. typhi and S. paratyphi and to Vi antigens of S. typhi. The results suggest that the carrier state may be the consequence of a specific defect in cell-mediated immune responses to S. typhi.