Induction of tissue transglutaminase in human peripheral blood monocytes by intracellular delivery of retinoids.

Human peripheral blood monocytes (HPBM) from normal donors, isolated by counter-current centrifugal elutriation into two subpopulations, showed no significant difference in their ability to differentiate in vitro into macrophages as determined by induction of a protein cross-linking enzyme tissue transglutaminase (TGase). The two subpopulations were equally responsive to the augmenting effect of recombinant interferon-gamma (rIFN-gamma) on expression of tissue TGase. In vitro maturation and treatment with rIFN-gamma of HPBM were associated with increased binding of tritiated retinol. Intracellular delivery of retinol rendered this hormone active in inducing the differentiation of HPBM. The retinoid-induced expression of tissue TGase was the result of increased accumulation of the enzyme peptide and not activation of preexisting enzyme. We propose, therefore, that maturation of HPBM, induced by in vitro culture or treatment with rIFN-gamma, is associated with acquisition of cell surface receptors for serum retinol-binding protein.