Characterization of Lymphocyte Subpopulations in Sheep by Rosette Formation, Adherence to Nylon Wool and Mitogen Responsiveness

Sheep peripheral blood lymphocytes have been studied using a number of surface markers. Thus 16.6 +/- 2.4% (mean +/- S.E.) were surface immunoglobulin positive (sIg+) by direct immunofluorescence, 35.9 +/- 2.1% formed Fc rosettes with bovine red blood cells (RBC) sensitized with rabbit antibody (Fc+) and 28.4 +/- 2.0% formed rosettes with sheep red blood cells (RBC) in the presence of 4% dextran (DS+). The percentage of both Fc+ and DS+ lymphocytes tended to increase with age of the animals. Demonstration of these markers allowed computation of two further subpopulations: null cells lacking sIg and a receptor for sheep RBC, and Fc.null cells lacking a receptor for Fc and sheep RBC. The former population, which contained a proportion of Fc+ lymphocytes comprised 49.8 +/- 3.8% of blood lymphocytes and the latter 38.4 +/- 3.0%. Separation on nylon wool columns, selective rosette enrichment and depletion on density gradients and stimulation with phytomitogens have shown sIg+ and Fc+ lymphocytes to be nylon wool adherent and unresponsive to phytohaemagglutinin (PHA) and Concanavalin A (Con A) and DS+ lymphocytes to be nylon wool non-adherent and responsive to PHA and Con A. The data also indicates a major overlap of the lymphocyte subpopulations bearing sIg and Fc which are apparently B lymphocytes. Moreover these data support the contention that E-rosette formation with sheep RBC in the presence of dextran is a marker for sheep T cells. The data also indicates tha Fc.null cells are T cells, eluting in the non-adherent fraction from nylon wool. It is probable that a proportion of these cells bear a SRBC receptor too weak for present detection methods.