Cyclosporin receptors on human lymphocytes
Ryffel, B.; Götz, U.; Heuberger, B.
Journal of Immunology 129(5): 1978-1982
1982
ISSN/ISBN: 0022-1767 PMID: 6981669 Document Number: 188589
Utilizing (3H)-cyclosporin C (3H-CS-C), a dihydroderivative of cyclosporin A (CS-A), an assay for cyclosporin receptors on human peripheral blood lymphocytes was developed. The specific binding of (3H)-CS-C was saturable, time-dependent and reversible. A Kd of 1.2 .times. 10-7 M and a maximum binding capacity (Bmax) of 7 pmol/106 cells was calculated from equilibrium binding studies. A Scatchard analysis confirmed a single population of high affinity binding sites and .apprx. 7 .times. 105 sites/cell. Kinetic analysis of specific binding at 37.degree. C yielded a pseudo-first-order rate association constant of 1.1 .times. 106 M-1 min-1 and a zero-order dissociation rate constant of 0.19 min-1. The Kd 1.7 .times. 10-7 M calculated from kinetic studies agreed well with the value of 1.2 .times. 10-7 M determined in equilibrium binding studies. Regarding the specificity of binding, (3H)-CS-C binding to lymphocytes was inhibited with CS-A and CS-C; no inhibition with the biologically inert keto-CS-A was observed. Mitogens and various growth factors did not compete for the binding site when added simultaneously with the radiolabel. Pretreatment with T cell mitogens such as PHA or the OKT3 antibody reduced (3H)-CS-C binding significantly. The binding site for CS-A apparently is closely associated with the mitogenic receptor on lymphocytes.