A study measured two immune proteins, LL‑37 and hBD2, in kids with a lung condition called post‑infectious bronchiolitis obliterans and found both were higher than in healthy children, but the levels didn’t relate to age, gender, weight, or vitamin D.

The antimicrobial peptides (AMPs) human β-defensins and cathelicidin (LL-37) are key factors in innate and adaptive immune responses of the respiratory tract and play an important role in many respiratory diseases. No data are available in the literature about the levels of these AMPs in paediatric patients with post-infectious bronchiolitis obliterans (BO). This study aimed to determine human β-defensin 2 (hBD2) and LL-37 levels and compare between post-infectious BO patients and the control group. The patients diagnosed with post-infectious BO between September 2012 and 2013 and age- and-gender matched healthy controls were enrolled in this multi-center study. Serum hBD2 and LL37 levels were determined with the enzyme-linked immunosorbent assay method. Sixty-three post-infectious BO patients and 65 healthy children (median age 73 ± 55 and 78.74 ± 36.32 months, respectively) were enrolled in the study. The mean of hBD2 levels in patients and the control group were 1.06 ± 0.24 and 0.67 ± 0.72 ng/mL, respectively (P < 0.001). The mean of LL-37 levels in patients and the control group were 72.13 ± 29.06 and 50.10 ± 21.98 ng/mL, respectively (P < 0.001). No correlation was found between these AMPs levels and chronological age, age at the time of diagnosis, gender, Z-scores of weight and length, hospitalization numbers, the disease history before diagnosis and 25-OH D vitamin levels. This is the first study to demonstrate the higher levels of serum hBD2 and LL-37 levels in paediatric post-infectious BO patients. These AMPs may have important roles in the immune systems and pathogenesis of these patients.