Measurement of the tissue distribution of immunoperoxidase staining with polyclonal anti-BCG serum in lung granulomata of mice infected with Mycobacterium tuberculosis.

Mice inoculated with Mycobacterium tuberculosis, strain H37Rv were used as a model of human tuberculosis. The microanatomical location of immunoperoxidase staining with a polyclonal anti-BCG serum was within macrophages and appeared granular rather than delineating whole bacilli. Immunoperoxidase staining appears to demonstrate degraded mycobacterial antigens from disrupted organisms and so reflects prior turnover of bacilli. On Ziehl-Neelsen staining, intact or almost intact bacilli are seen and so the extent of this form of staining reflects the current bacillary load. Both methods have limited sensitivity, but with larger mycobacterial loads the area of immunoperoxidase stain measured on a semi-automated image analyser correlated with the numbers of bacilli observed. The immunoperoxidase method will be useful in the evaluation of residual antigen in studying the pathogenesis of experimental murine tuberculosis. In human mycobacterial granulomata, this immunohistochemical technique should provide an alternative method of estimating the extent of bacillary load: this approach may also provide evidence of mycobacterial infection from residual antigen deposits in the tissue when whole bacilli have been successfully cleared.