1 alpha,25-Dihydroxyvitamin D3 receptors in human thymic and tonsillar lymphocytes

In vitro activated human peripheral blood lymphocytes possess the receptor protein for 1 alpha,25-dihydroxyvitamin D3 (1,25(OH)2D3). In the present study we have examined whether activated lymphocytes that occur in vivo in human thymuses and tonsils also possess receptors for 1,25(OH)2D3. Freshly isolated lymphocyte preparations, from five separate surgical specimens of thymus and tonsil, were depleted of monocytes and examined, before and after fractionation on a density gradient of Percoll, for [3H] 1,25(OH)2D3 binding by means of sucrose density gradient sedimentation, by saturation analysis of the binding, and by DNA-cellulose chromatography. The state of activation of the lymphocyte preparations was determined using [3H] thymidine incorporation, DNA and RNA quantitation (using acridine orange), and by determining the presence or absence of markers of activation (interleukin-2 receptor, transferrin receptor, and HLA-DR molecules). In both the thymic and the tonsillar lymphocyte preparations we detected a 1,25(OH)2D3-binding molecule possessing sedimentation coefficient of 3.3 S and dissociation constant of 10(-10) M as well as DNA binding capability. In thymic lymphocytes, the 1,25(OH)2D3 receptor concentration correlated positively with the number of lymphocytes expressing the transferrin receptor (r = 0.84; p less than 0.05). In addition, in both thymic and tonsillar lymphocytes the concentration of 1,25(OH)2D3 receptors correlated positively with the number of cells in the G1a phase of the cell cycle (r = 0.79, p less than 0.01, and r = 0.88, p less than 0.001 for thymic and tonsillar lymphocytes, respectively). In contrast, the 1,25(OH)2D3 receptor concentration in these preparations did not correlate with the rate of cell proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)