Kinetics of the immune response associated with tularemia: comparison of an enzyme-linked immunosorbent assay, a tube agglutination test, and a novel whole-blood lymphocyte stimulation test.

We have developed and evaluated a novel and simplified whole-blood lymphocyte stimulation assay that focuses on the measurement of gamma interferon after 24 h of stimulation with whole-cell tularemia antigen and a tularemia enzyme-linked immunosorbent assay (ELISA) based on highly purified lipopolysaccharide antigen. Comparison of the kinetics of the two assays and those of the traditional tube agglutination test shows that the cellular immune response can be detected earlier by the lymphocyte stimulation assay. This test already shows a high proportion of positive results during the first week after the onset of the disease, may be applicable in everyday laboratory practice, and has the potential of changing routine diagnostics for tularemia. The new ELISA has a high sensitivity and becomes positive to a high degree during the second week of disease.