Homing receptor expression and migration of activated lymphocytes.

The experiments show that homing receptors are regulated in a complex fashion during initial cellular activation: Signals leading to blast formation induced either: --a decrease of homing receptor expression in the majority of blasts; --an increase of the Mel-14 expression in 20-40% of the blasts, and --a selective down-regulation in the capacity to bind to Peyer's patch HEV even under conditions, where binding to peripheral HEV is high. Submitogenic stimuli in partially activated cultures induce a rise in Mel-14 antigen expression and binding to peripheral node HEV, whereas Peyer's patch binding is unchanged or lowered. Thus, a selective and differential regulation of organ-specific homing receptors takes place under distinct activation conditions. The mucosal system-related receptor is more easily down-regulated upon activation. The in vivo homing experiments indicate that mitogen activation induces one dominant migratory phenotype. Alterations in homing receptor expression seem to be associated with changes in further cellular functions leading to reduced entry into lymphatic tissues and increased localization of these cells in lung or liver. The mechanisms regulating the differential expression of organ-specific homing receptors and additional homing-relevant properties of the cells are still unknown.