Characterization of lymphocyte subpopulations in sheep by rosette formation, adherence to nylon wool and mitogen responsiveness

Abstract

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 that 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.