Lymphocyte subpopulations in lymph from BCG-vaccinated sheep injected with tuberculin PPD

The subpopulations of lymphocytes in efferent popliteal lymph from BCG-vaccinated sheep were studied during the delayed-type hypersensitivity (DTH) response to tuberculin purified protein derivative (PPD). There was an initial 'shutdown' or transitory decrease in cell output 12 h after the subcutaneous injection of PPD. During this time the output of lymphocytes with surface immunoglobulin (sIg+), Fc-receptors and those forming rosettes with sheep erythrocytes in saline (E+) or in Ficoll (Efic+) were reduced, suggesting that all subpopulations were affected equally. The total cell output increased during the course of the blast cell response that followed the 'shutdown', but again the proportion of Efic+ cells remained relatively constant. In some sheep, the proportion of sIg+ cells and cells with receptors for complement (C') increased to a peak 4 days after challenge, before returning to base levels. With most sheep, however, the numbers of sIg+ cells did not change greatly during the blast cell response. Lymph cells obtained during the DTH response were found to enhance the in vitro response of sensitized lymphocytes to PPD. In one sheep this 'help' progressively increased from 108 h until 324 h, the last sample taken. These experiments failed to detect the presence of suppressor cells in lymph that could play a role in regulating the blast cell response of lymph-borne cells to PPD.