Isolation and identification of equine lymphocytes and monocytes

Various cell populations of equine mononuclear leukocytes were identified and isolated. Mononuclear leukocytes were concentrated by isopyknic centrifugation, using a solution of Ficoll and Hypaque. Three additional techniques were explored to separate monocytes from lymphocytes, and 3 methods were used to separate lymphocyte types. Cytochemical techniques for the detection of nonspecific esterase readily distinguished equine monocytes from lymphocytes. Peripheral blood lymphocytes were separated into at least 2 populations. One population had surface traits identical to thymocytes [ie, they readily bound peanut agglutinin, but lacked receptors for complement or immunoglobulin (Ig) and did not have surface Ig, as detected by immunohistochemical techniques]. This population could be isolated, using nylon-wool columns, or by depletion of complement- and Ig-binding cells during centrifugation. The other class of lymphocytes had equine complement receptors, Ig receptors, and detectable surface Ig, but was not bound by peanut agglutinin. Using rosetting techniques followed by centrifugation, this latter population was enriched. These studies provided means of isolating and detecting equine monocytes, B lymphocytes, and T lymphocytes.