LYMPHOCYTOSIS OF GAMMA DELTA T-CELLS IN HUMAN EHRLICHIOSIS/

The majority of T cells in peripheral blood express a T-cell receptor (TCR) comprised of alpha and beta chains, An alternate form of the TCR is comprised of gamma and delta chains, These gamma/delta T cells are associated with certain infectious lesions, and modestly elevated in peripheral blood in certain disease states. Human ehrlichiosis is char acterized by hematologic abnormalities including multi-lineage cytopen ias. In most cases reported, a lymphocytopenia has been present either at diagnosis, or at some time during the illness. Early in the course of antibiotic treatment (48-72 hours), the lymphocytopenia corrects i tself and is rapidly followed by a lymphocytosis of T cells that expre ss CD3, but are negative for CD4 and CD8, as well as the major form of the TCR formed by the alpha/beta heterodimer, Instead, these CD3(+)4( -)8(-) T cells express the gamma/delta heterodimer associated with V g amma 9 and V delta 2 chains, a population of cells usually the distinc tive minority of peripheral blood T cells, but constituting the major phenotype of peripheral gamma/delta T cells.