Inverse correlation of programmed death 1 (PD-1) expression in T cells to the spinal radiologic changes in Taiwanese patients with ankylosing spondylitis.

Programmed death 1 (PD-1) has been shown to be involved in the negative regulation of the immune response. However, the role of PD-1 in ankylosing spondylitis (AS) has not been studied. Therefore, we analyzed the expression of PD-1 in peripheral blood mononuclear cells (PBMC) from patients with AS. Twenty-three AS patients, 20 rheumatoid arthritis (RA) patients, and 25 normal healthy subjects were recruited. The percentage of the PBMC and PD-1 levels in these subjects were measured by flow cytometry. A higher percentage of CD4+ T cells was noted in AS patients than in healthy controls (37.53±1.65% vs. 31.55±0.92%, P<0.01), but a similar result was not observed with regard to CD3+ T lymphocytes, CD4+CD25 high+regulatory T cells, CD19+ B cells, and CD14+ and CD16+ monocytes/macrophages. PD-1 levels in PBMC were not significantly higher in AS patients than in RA patients or age- and gender-matched healthy controls and were also not correlated to the erythrocyte sedimentation rate, C-reactive protein, limitation of back flexion, and chest expansion in patients with AS. Of interest, the percentages of PD-1+CD3+ T cells and PD-1+CD4+ T cells were significantly lower in AS patients with higher modified Stokes Ankylosing Spondylitis Spinal Scores (mSASSS ≥30) than in those with lower mSASSS (<30; 0.07±0.04% vs. 0.42±0.14%, P<0.05; 0.06±0.03% vs. 0.40±0.14%, P<0.05, respectively). These results have suggested that the increased number of T helper cells lacking PD-1 may contribute to the spinal radiologic changes in AS patients.