Nonspecific acid esterase activity as a marker for canine T lymphocytes

Canine T lymphocytes are as yet poorly defined. Since focal paranuclear positivity for nonspecific esterase (alpha-naphthyl acetate esterase--ANAE) has been shown to be a reliable marker for T cells in humans and mice, canine lymphoid tissue sections, and cell suspensions were stained for this enzyme. Sections of five lymph nodes and 11 puppy thymuses displayed the same distribution patterns of focally ANAE-positive cells as were found in humans and mice in both organs: in thymuses only the medulla contained positive cells, and in lymph nodes only the thymus-dependent, paracortical zones, but not central areas of germinal centers, displayed focal ANAE reactivity. Furthermore, 56-78% of peripheral blood mononuclear cells, 60-71% of thoracic duct lymphocytes, and 10-15% of suspended thymus cells were positive for ANAE. It is concluded that focal ANAE reactivity is a marker for a canine T cell subpopulation.