Analysis of cell division among subpopulations of lymphoid cells in sheep. II. Peripheral lymphocytes.

The number, distribution and surface phenotype of dividing cells in lymph nodes and blood and differences between the cell-cycle status of lymphocyte subpopulations were studied in lambs using double-labelling techniques. Dividing cells were labelled in vivo for various time periods with 5-bromo-2-deoxyuridine (BrdU). After removal of lymphoid tissues, the proportions of constituent lymphocyte subpopulations which had synthesized DNA during the labelling period were measured by flow cytometry or immunohistochemistry using a panel of monoclonal antibodies (mAbs) specific for sheep lymphocyte differentiation antigens and MHC class I and class II antigens in conjunction with an anti-BrdU mAb. There was a higher overall level of cell division in the ileocaecal lymph node than in either the prescapular or parathymic lymph nodes. In all three lymph nodes, the majority of lymphocytes which incorporated BrdU occurred in B-cell follicles or germinal centers. CD4+ and CD8+ T cells had a higher level of cell division (LI 5-14%) than those recognized by mAb 197 (CD4- CD8- subset) (LI less than or equal to 3%).