Foot pad enlargement as a measure of induced immunity to Mycobacterium leprae.

Foot pad enlargement (FPE) has been used as a measure of induced immunity to M. leprae, FPE peaked at 2-3 days, but it sometimes persisted for 4 weeks or more. Both as the inducing and eliciting antigen, heat-killed M. leprae were effective, and the optimum dose was about 1 x 10(7) bacilli. Higher doses were associated with flattening of the dose-response curve. Disrupted bacilli were not effective in immunizing mice, but they elicited FPE responses in mice immunized with intact bacilli. Cord factor was not found to have adjuvant activity for M. leprae. In immunization, the intradermal route was confirmed to be more effective than the foot pad route; the subcutaneous route was effective in providing protection against infection. FPE tests were used to investigate the steps of standard purification procedures for M. leprae in armadillo livers. A trypsin-chymotrypsin digestion step was found to be harmful to immunogenicity in one of two experiments.