Effect of active vitamin D on expression of co-stimulatory molecules and HLA-DR in renal transplant recipients

Full activation of T cells requires 2
distinct but synergistic signals. The first is the T-cell
antigen receptor, which is antigen specific, and the
second is activation of co-stimulatory signals. Active
vitamin D (1, 25-dihydroxyvitamin D3) decreases
T-cell activation and proliferation, inhibits
differentiation and maturation of dendritic cells,
and induces tolerogenic dendritic cells. These
immunoregulatory effects may be due, at least in
part, to changes in cytokine secretion and
expression of co-stimulatory molecules. The use of
active vitamin D has been reported to improve
allograft survival, decelerate loss of allograft
function, and prevent acute rejection. This study
was conducted to assess the effect of active vitamin
D on the expression of co-stimulatory molecules and
HLA-DR in renal transplant recipients.
Materials and Methods: In this prospective study,
we enrolled 24 renal transplant recipients who had
undergone a transplant 6 to 18 months earlier, had
stable allograft function, and were without
episodes of allograft dysfunction or febrile illness in
the previous 2 months. Participants were
administered oral calcitriol 0.5 μg daily for 4 weeks.
Expression of HLA-DR, CD28, CD86, and CD40 in
peripheral blood leukocytes was assessed by flow
cytometry before and after calcitriol administration.
Results: Compared to baseline levels, expression of
HLA-DR decreased by 16.8%; expression of CD28, by
30%; of CD40, by 31.2%; and of CD86, by 36.7%.
Conclusions: In renal transplant recipients,
decreased expression of co-stimulatory and HLA-DR
molecules occurred after treatment with active
vitamin D. Such changes may be involved in
increasing allograft survival.