PURPOSE: Acquired immunity is impaired in hemodialysis (HD) patients, and decreased T cell number may contribute. Receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin (OPG) are expressed in cells of the immune system and affect T cell development, homeostasis and proliferation. Serum levels of RANKL and OPG and their relation to blood T cell number were evaluated in HD patients.METHODS: Thirty-four HD patients and 20 healthy controls participated in the study. Serum RANKL and OPG were measured by ELISA and T cell number was assessed by flow cytometry.RESULTS: Median RANKL concentration did not differ between HD patients and healthy volunteers (300.00 pmol/L; range, 3,340.00 vs. 330.00 pmol/L; range, 440.00 pmol/L; p = 0.528). Median OPG was markedly higher in HD patients than in healthy volunteers (13.12 ± 4.71 vs. 4.71 ± 0.93 pmol/L, p < 0.001). The T cell count was significantly lower in HD patients than in healthy controls (1,177.00 ± 567.71 vs. 1,519.80 ± 594.96 cells/mm(3), p = 0.044). In HD patients, blood T cell number was correlated positively with serum RANKL (ρ = 0.462, p = 0.007) and negatively to serum OPG (r = -0.449, p = 0.008).CONCLUSION: Serum OPG concentration is markedly increased in HD patients and may contribute to decreased blood T cell count and impaired acquired immunity that characterizes this population.