Figure 2.

1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] inhibits regulatory T (Treg) and conventional T (Tconv) cell proliferation. (a) The effect of graded doses of 1,25(OH)₂D₃ on Treg or Tconv cell proliferation, stimulated with anti-CD3/anti-CD28 monoclonal antibody-coated microbeads and in the presence of interleukin-2 (IL-2). Cell proliferation as assayed by [³H]thymidine incorporation at day 4 of culture and expressed as mean ± SD. Data are representative for five independent experiments. (b) Percentage growth inhibition of Treg and Tconv cells upon treatment with 1,25(OH)₂D₃ at 1, 10 and 100 nm was calculated. Data are the cumulative results of five independent experiments using cells isolated by high purity flow cytometric cell sorting. *P< 0·05 when comparing the degree of growth inhibition between Treg and Tconv cells. Effect of 1,25(OH)₂D₃ (100 nm) on CD69 expression (y-axis), in (c) Treg and (d) Tconv cells labelled with carboxyfluorescein succinimidyl ester (CFSE; x-axis), 24 or 48 hr after activation. (e) Cell division of Treg and Tconv cells as analysed by CFSE dilution (x-axis) on day 5 with and without addition of 100 nm 1,25(OH)₂D₃. Data are representative for three independent experiments performed with cells isolated by high-purity flow cytometric cell sorting, obtained from different donors.