FIG.3.

Vaccination with mc²6020 confers long-term survival and induces milder lung pathology in immunocompetent mice. (A) Survival of immunocompetent C57BL/6 mice (n = 10) immunized subcutaneously with a single dose of mc²6020 (○) or BCG-P (▴) and challenged 3 months later with virulent M. tuberculosis Erdman by the aerosol route. Unvaccinated mice served as naive controls (•). (B and C) Lungs of mice challenged 7 months after vaccination with a single dose of mc²6020 by the subcutaneous route. (B) Low-power photomicrograph showing scattered areas of pneumonia adjacent to bronchioles, with limited localized spread into the adjacent parenchyma. (C) Higher-power magnification of lung lesions in these mice showing the intense localized lymphocytic perivascular accumulations and infiltration of numerous macrophages filling the adjacent alveolar spaces. (D and E) More-severe spreading lung lesions in unvaccinated mice compared with those in vaccinated mice. (D) Low-power photomicrograph showing multiple areas of extensive pneumonia. (E) Affected areas of the lung showed granulomatous pneumonia and were consolidated with loss of air spaces, caused by the extensive diffuse infiltration of epithelioid cells accompanied by large numbers of lymphocytes.