sheep cell test [AS, sceap + L, cella, storeroom, testum, crucible] , a method that mixes human blood cells with the red blood cells of sheep to determine the absence or the deficiency of human T lymphocytes. When mixed with human blood cells, the red blood cells of sheep cluster around the human T lymphocytes and form characteristic rosettes. An electron microscope is used to identify the rosettes. An absence or a decrease in the number of rosettes indicates a deficiency or absence of T cells. The sheep cell test is used to diagnose several diseases, such as DiGeorge’s syndrome, that decrease or destroy the cellular immunity provided by T cells.
