Chen et al. discovered that peripheral blood mononuclear cell from AS patients with severe sacroiliitis had greater ability to express bone morphogenic protein genes by tumor necrosis factor-α and interleukin-1β stimulation than AS patients without severe sacroiliitis [31], which means that severity of sacroiliitis might have correlation with potency of new bone formation in AS. This evidence concerns the gene TNF and Sacroiliac arthritis.