Calprotectin has long been identified as an inflammation-related protein which is also active in both innate and adaptive immune responses in inflammation. This study describes that the baseline calprotectin level in serum was positively concerned with expressions of IL-1β, IL-17 and TNF-α in AS patients. Hence, a more significant and more rapid change in calprotectin might indicate a reduction of inflammation in AS patients post-treatment, which might envisage a better response to treatment. 

To examine the association of serum calprotectin with risk and severity of ankylosing spondylitis (AS), and to investigate its levels for predicting the treatment responses. 

A total of 260 healthy and 262 AS patients were selected for the analysis. One hundred and forty-two active AS participants received pharmaceutical therapy and assessed for the clinical response as per the ASAS 40 improvement criteria. The blood sample from HCs and AS patients were collected at enrollment and from 142 active AS patients at month 1, 3, 6 following the treatments. Serum calprotectin, TNF-α, IL-1β, and IL-17 expressions were also assessed using the ELISA.

The baseline calprotectin was of excellent diagnostic value for AS as per the Receiver Operating Curve (ROC) analysis. The AS patients exhibited a remarkably higher expression of calprotectin than HCs. A positive association was seen between Calprotectin level and pain VAS, CRP,  BASDAI, BASFI, ESR, and PGA and the patients with greater calprotectin levels exhibited high TNF-α, IL-1β, and IL-17 expressions. Among active AS patients, the calprotectin levels reduced notably from baseline to 1, 3 or 6 months after the treatment. Moreover, the patients who obtained ASAS 40 exhibited a more significant change in the levels of calprotectin during the first month and this shift in calprotectin during the first month helps to predict the SAS 40 patients with AUC of 0.691.

For assessing severity and risk of AS, serum calprotectin level could be a promising biomarker and the change of calprotectin in the first post-operative month might predict more positive treatment response within active AS patients.