Objective To study the influence of residual methylene blue after plasma viral inactivation on the human immune cell function by using the peripheral blood mononuclear cell(PBMC) .Methods PBMC were isolated by adopting the Ficoll‐Hypaque density gradient centrifugation method and co‐cultured for 72 h in presence of specific T cell stimulating factors(Anti‐CD3/28 and Anti‐CD28) ,with or without different concentration of methylene blue .The culture supernatant was collected and detected the cyto‐kines secretion situation by ELISA .After 66 h culture ,CCK‐8 dye was added and continueously cultured for 4-6 h ,the prolifera‐tion was determined at A450 .Results The high‐concentration doses of methylene blue (1 .25 ,2 .5 ,5 μmol/L groups) had signifi‐cantly inhibiting effect on the proliferation of PBMC stimulated by Anti‐CD3/28(P< 0 .01) ,its OD value was decreased from 0 .897 ± 0 .385 to 0 .632 ± 0 .334 ,0 .524 ± 0 .254 and 0 .445 ± 0 .287 respectively ,showing certain dose dependent effect .The high concentrations of methylene blue (1 .25 ,2 .5 ,5 μmol/L groups) could down‐regulate interleukin(IL)‐17a ,IL‐10 and interferon (IFN)‐γ secreted by anti‐CD28 induced PBMC ,moreover showing a dose dependent effect .1 .25 ,2 .5 ,5 μmol/L methylene blue af‐fected the IL‐17a level secreted by PBMC from (406 ± 57)pg/mL descending to (276 ± 38) ,(192 ± 31) ,(134 ± 24)pg/mL respec‐tively ;affected PBMC to secrete IL‐10 ,its level was reduced from (184 ± 15) pg/mL to (132 ± 13) ,(110 ± 12) ,(42 ± 8)pg/mL ;af‐fected PBMC to secrete IFN‐γ,its level was deduced from (4 512 ± 187)pg/mL to (2 876 ± 143) ,(2 234 ± 153) ,(1 988 ± 112)pg/mL respectively .Conclusion High concentrations of methylene blue (≥1 .25 μmol/L ) has the significant inhibiting effect on the proliferation and cytokine secretion functions of PBMC .In other words ,the residual methylene blue concentration in viral inactiva‐tion plasma (≤0 .33 μmol/L) has no obvious effect on the immune function of PBMC ,but whether this concentration of methylene blue having the effect on human pure T cell immune function needs to be further evaluated and studied .