Quantification of BCG-induced reactions of T and B areas in peripheral lymphoid organs of young adult BALB/c mice. A histomorphometrical and autoradiographical study.

Significant structural alterations of the axillary lymph nodes and spleens were revealed by histomorphometry following intraperitoneal injection of BCG into young adult BALB/c mice. The relative proportions of the germinal center areas were increased in lymph nodes as well as in spleens. The overall proportion of the B cell areas, however, showed a significant increase only in the spleens, compared to a significant reduction in the lymph nodes. By contrast, T cell areas appeared significantly reduced in the spleens, while their size was almost doubled in the lymph nodes. The labeling index in the lymph node paracortical areas was also doubled autoradiographically. The structural changes in the lymph nodes and spleens differed not only in quality, but also in their time course. In lymph nodes, the altered proportions of the T and B cell areas persisted from the second through the sixth week after BCG treatment. By contrast, structural changes in the spleen began to subside 2 weeks after treatment, and after 6 weeks the proportions of the T and B cell areas in the spleen had returned to normal. These quantitative morphologic findings suggest a difference in the functional roles of lymph nodes and spleen in the systemic immune response to BCG.