REGULATED EXPRESSION OF GP130 AND IL-6 RECEPTOR-ALPHA CHAIN IN T-CELLMATURATION AND ACTIVATION

The functional receptor for the inflammatory cytokine IL-6 is composed of the ligand binding IL-6 receptor a chain (IL-6R alpha) and the sig nal transducing chain gp130, which is a shared component of multiple c ytokine receptors. We analyzed the surface expression of gp130 and IL- 6R alpha in thymocytes and peripheral T cells. While ail thymocytes ex pressed gp130 throughout thymic maturation, they gained expression of IL-6R alpha at the CD4 or CD8 single-positive stage. Approximately 10- 30% of the CD4(-)CD8(+) and 40-50% of the CD4(+)CD8(-) thymocytes expr essed IL-6R alpha. Within the CD4+CD8- population, the IL-6R alpha(-) subpopulation was cortisone sensitive, appeared immature according to the cell surface markers expressed and failed to proliferate after TCR cross-linking. Peripheral T cells were predominantly gp130(+) and IL- 6R alpha(+), but downregulated gp130 and IL-6R alpha expression upon T CR engagement in vitro and in vivo. Peripheral gp130(low/-)IL-6R alpha (low/-) T cells expressed surface markers characteristic of memory T c ells, We show that gp130 and IL-6R alpha are expressed in a regulated manner in T cells, depending on the developmental and functional stage .