OBJECTIVEThis study aims to investigate the possible role and significance of soluble programmed death-1 (sPD-1)  /soluble programmed death ligand 1 (sPD-L1) in the immune pathogeneses of recurrent aphthous ulcer (RAU).

METHODSA total of 30 RAU cases (18 cases of minor RAU, 5 cases of major RAU, and 7 cases of herpetiform ulcers) were enrolled in this study. A total of 18 healthy people served as controls. Lymphocyte subsets (CD3⁺, CD4⁺, CD8⁺, CD19⁺, and CD16⁺+56⁺) were investigated by flow cytometric analysis. Humoral immunity (IgG, IgA, IgM, C3, and C4) was explored by nephelometry immunoassay. The sPD-1 and sPD-L1 protein levels in the sera of RAU patients were investigated by enzyme-linked immunosorbent assay. The correlations of the sPD-1 and sPD-L1 protein levels with the immune status and clinical characteristics of the RAU patients were analyzed by SPSS 19.0.

RESULTSThe number of CD4+ T cells decreased and the levels of IgM antibodies increased in the RAU patients relative to those in the normal controls (P<0.05). The sPD-1 and sPD-L1 protein levels in the RAU patients were significantly higher than those in the control group (P<0.05). Meanwhile, the sPD-1 and sPD-L1 protein levels in the patients with minor and major RAU were significantly higher than those in the control group (P<0.05). By contrast, no significant difference was found in the patients with herpetiform RAU (P>0.05). Positive correlations were noted between the sPD-1 protein level and the CD19+ cell frequency or C4 level (r₁=0.389, P₁=0.034; r₂=0.382, P₂=0.037).

CONCLUSIONSCellular immune hypofunction and humoral immunity disorders were found in the RAU patients. The PD-1/PD-L1 signaling pathway, which might be influenced by the involvement of sPD-1 and sPD-L1 proteins to a certain extent, may play some roles in the immune pathogenesis of RAU.