Characterization and maturation of alveolar macrophages procured from BCG-induced pulmonary granulomas.

Pulmonary macrophages from BCG-induced granulomas were separated according to their densities into six fractions by the use of discontinuous gradients of Percoll. A comparative study of distribution profiles of lavaged rabbit alveolar cells obtained 16 or 28 days after vaccination revealed that 16 days after vaccination there were small numbers of low-density cells (fractions 1 and 2) and large numbers of high-density cells (fractions 4 and 5). In contrast, 28 days after vaccination there was a marked increase in the numbers of macrophages in fractions 1 and 2 and relatively small numbers of high-density cells in fractions 4 and 5. Macrophages of fractions 1 and 2 (densities of 1.030-1.050) were large and mature in appearance and expressed low levels of acid phosphatase and beta-glucuronidase. Although macrophages in fraction 1 commonly showed signs of degeneration, they were the most active in terms of reducing nitroblue tetrazolium (NBT). Macrophages of fractions 3 and 4 (densities of 1.050-1.068) were smaller, appeared intact and fully mature, showed no signs of degeneration, and expressed the highest levels of the above enzymes, although their ability to reduce NBT was less than that in cells from fractions 1 and 2. The cells of fractions 5 and 6 (densities of 1.068-1.074) were small, expressed low levels of the above enzymes, and their ability to reduce NBT was minimal. These results indicate that density may be a reliable correlate of the maturity of macrophages harvested from BCG-induced granulomas.