Erythrocyte-Rosetting Properties of Feline Blood Lymphocytes and Their Relationship to Monoclonal Antibodies to T Lymphocytes

Abstract

Rosette formation of feline peripheral blood leukocytes with guinea pig (GP) and gerbil (G) erythrocytes (E) has been shown in an earlier study to identify T lymphocytes expressing helper and suppressor cell activity, respectively. This T lymphocyte distinction was based on the removal of the E-rosetting populations from peripheral blood leukocytes (PBL) and the subsequent functional evaluation of the remaining cells in a pokeweed mitogen (PWM)-induced synthesis of immunoglobulin (Ig). In the present study, we demonstrate a direct helper and suppressor function of GPE- and GE-rosetted cells, respectively, wherein the induction of Ig synthesis is altered in a positive or negative way by the addition of the cells to a control target population. A pan-T monoclonal antibody (mAb), CT843, and mAbs to the CD4 (CT248) and CD8 (CT87) subsets are also described; their specificities are established in functional assays, the PWM-induced Ig synthesis and the production of interleukin-2 following Concanavalin A stimulation of PBL, and a biochemical analysis of the surface membrane antigens detected by the mAbs. Immunopreclpitation and SDS-PAGE analyses showed CT248 to react with a ~60-kDa protein under both reducing and nonreducing conditions. Under reducing conditions, CT87 reacted with one subunit at ~35 kDa; a second faint band at ~39 kDa was poorly resolved. mAb CT843 detected a heterodimer of ~70 and ~60 kDa under both reducing and nonreducing conditions. The relationship of the mAbs to E-rosetting was examined in FACScan analyses and rosette Inhibition studies. The percentage of GE-rosetting cells agreed with the percentage of cells stained with the CD8 mAb, whereas a comparison of GPE-rosetting and staining with the CD4 mAb showed variability. The binding of GE to PBL was blocked by pretreatment of PBL with the CD8 mAb, whereas no inhibition of GPE rosettes was observed with any of the mAbs. In a previous study, we had shown that an overnight culture of feline PBL at 37°C leads to the development of a second population of GPE-rosetting cells, also having a helper function. The relationship of the two GPE-rosetting populations to the CD4 mAb, CT248, was examined in rosette depletion studies and FACScan analyses. It was found that depletion of the GPE-rosetting cells from fresh, i.e., Day 0 cells, removed only a small percentage of cells reactive with the CD4 mAb, whereas GPE-rosette depletions performed on Day 1 PBL, which contained both populations of GPE-rosetting cells, removed almost all cells reactive with this antibody. The latter study suggests that the GPE-rosetting phenomenon is detecting two subsets of CD4 cells with T helper function, those present in fresh blood and those acquiring the GPE receptor after an overnight culture.