Suppression of tuberculoimmunity in mice by Evans blue dye.

Evans blue dye, which acts as an adjuvant in mice to promote induction of cell-mediated immunity, was found earlier to apparently act contrarily and decrease tuberculoimmunity. This phenomenon was investigated here in a long-term experiment examining the persistence of the suppressed immunity. Systemic suppression after injection of only 1 mg of dye was confirmed and was found to last for more than 2 weeks but less than 11 weeks. Localized evidence for dye-caused depression of tuberculoimmunity also was seen by the development in dye-injected mice immunized with emulsified whole bacilli of caseating tubercles at sites of pulmonary infection, a very rare type of pathology for tuberculosis in mice. The experiment, in addition, detected an aging-related decline in mice of resistance to tuberculosis evident by shortened survival, enlarged pulmonary tubercles, and increased susceptibility to systemic tuberculin reaction.