Studies of cellular and humoral immunity in typhoid fever and TAB vaccinated subjects.

An assessment of both humoral and cell-mediated immune responses to Salmonella typhi antigens in patients with acute typhoid infection, TAB inoculated subjects and in healthy controls is reported. Cell-mediated immunity as assessed by the leucocyte migration inhibition test (LMI), and developed in all cases with typhoid fever. Positive LMI was evident in the first week of the illness and was maintained during the evolution of disease and in some patients was still present after a year. It also developed at the end of 3 weeks in five out of nine TAB vaccinated subjects. Weakly positive LMI was noticed in only two of twenty asian and caucasian controls. Antibodies, determined by the standard Widal test, were significantly raised in both patients with typhoid fever and TAB inoculated subjects. The antibodies and cellular reactivity developed almost simultaneously but there was no correlation between the agglutination titres and LMI positivity, implying that they are independent of each other. Typhoid patients also showed significantly raised serum IgM and IgA levels and increased concentrations of secretory IgA in their saliva.