Distribution of cycling T lymphocytes in blood and lymphoid organs during immune responses

Proliferation of murine T lymphocytes in blood, lymph nodes, and spleen was studied in four in vivo stimulation systems, using BrdU pulse-labeling of DNA-synthesizing cells. The T cell response to the superantigen Staphylococ cus enterotoxin B (SEB) was studied in detail, V beta 8(+) T cells showed a peak of DNA synthesis 16-24 h after SEE injection, and the percentage of B rdU(+) CD4 and CDS T cells was higher in blood than in lymph nodes and sple en. DNA synthesis was preceded by massive migration of V beta 6(+) cells fr om blood to lymphoid organs, in which the earl! activation marker CD69 was first up-regulated, SEB-nonspecific V beta 6(+) cells showed minimal stimul ation but, when cycling, also expressed a high level of CD69, The other sys tems studied were injection of the IFN-gamma inducer polyinosinic:polycytid ylic acid, infection by the BM5 variants of murine leukemia virus (the caus ative agent of murine AIDS), and T cell expansion after transfer of normal bone marrow and lymph node cells into recombinase-activating gene-2-deficie nt mice, Ln each case, a peak of T cell proliferation was observed in blood . These data demonstrate the extensive redistribution of cycling T cells in the first few hours after activation. Kinetic studies of blood lymphocyte status appear crucial for understanding primary immune responses because cy cling and redistributing T lymphocytes are enriched in the circulating comp artment.