Proliferation of PPD-stimulated lymphocytes measured by sister chromatoid differential staining

Lymphocyte proliferation in response to tuberculin-purified protein derivative (PPD) stimulation was measured by bromodeoxyuridine incorporation followed by sister chromatid differential staining PPD-stimulated lymphocytes responded identically to phytohaemagglutinin (PHA) stimulated lymphocytes in that there was a steady increase in the number of second- and third-division metaphases with a corresponding decrease in the number of first-division metaphases. However, the mitotic index was considerably less in the PPD-stimulated cultures. The response of PPD-stimulated lymphocytes was largely the result of repeated divisions of a small number of lymphocytes. Donors who had been treated for tuberculosis showed greater numbers of second- and third-division metaphases than donors who had received BCG vaccination. Third-division metaphases than donors who had received BCG vaccination. Third-division metaphases were also present in the PPD and PHA 48-hr cultures, indicating tha lymphocytes can both respond to stimulation and divide faster than was previously recognized.