Immunological study of typhoid fever in man: humoral immune response.

Widal and indirect haemagglutination test were used to study the humoral immune response of 45 patients with typhoid fever. The Widal and IHA tests were positive in 41 (91.1%) and 42 (93.3%) of patients with typhoid fever after the second week of illness. Comparison between the Widal and IHA test showed that the latter was more sensitive as assessed by Wilcoxon matched-pairs signed-ranks test (p less than 0.01). The anti-LPS antibody belongs to all three classes of immunoglobulins namely IgG, IgM and IgA with the confinement mostly to IgG and IgM. It was found that the level of haemagglutinating enhancement activity was strongest in IgG class. The low level of anti LPS-antibody was found in healthy persons with the pattern of immunoglobulin class of antibody similar to that in patients with typhoid fever.