Interleukin-32 (IL-32), first reported as an inducer of tumor necrosis factor-α, is a pro-inflammatory cytokine involved in various chronic inflammatory diseases. This study evaluated the relationship between sputum IL-32 expression and severity of asthma.
IL-32 was determined in induced sputum samples of patients with asthma (n = 137) using sandwich ELISA. Relationships among sputum IL-32, airway obstruction (FEV1), inflammation (neutrophil and eosinophil % of the airway) and exacerbation frequency were evaluated.
Sputum IL-32 levels was well correlated with FEV1(%) in the total study subjects (r=-0.232, P = 0.006) and in the stable asthmatics (r=-0.312, P = 0.003). The levels was not different by use of inhaled steroid (P=0.068). When the all subjects were grouped into two inflammatory patterns by eosinophil% (over 3%, under 3%) or Neutrophils% (over 70%, under 70%), IL-32 levels was not different by the inflammatory patterns. IL-32 levels was significantly increased in the subject experiencing exacerbation (n=69) compared to those not experiencing exacerbation (n=53) (p<0.05). The sputum levels of IL-32 were well correlated with the annual rate of exacerbation in the total subjects.(r=0.231, P < 0.022)
Sputum IL-32 may be associated with severity of the asthma regardless of inhaled steroid treatment, and may be a surrogate marker for exacerbation risk of asthma.