Infants with whooping cough tend to have lower vitamin D levels but higher natural antimicrobial peptides (LL‑37 and HBD‑2) in their blood. The study shows the body can raise these peptides during infection even when vitamin D is low, and there’s no clear link between the two.

Most children with serious infection diseases suffer from malnutrition. Vitamin D participates in the immune response through endogenous antimicrobial peptides (AMPs) regulation. The aim of this study is to investigate the expression of 25-hydroxyvitamin D3 [25(OH)D3], AMPs [LL-37 and human β-defensin 2 (HBD-2)] in the children with pertussis. Serum levels of 25(OH)D3, LL-37, and HBD-2 were detected in 116 children with pertussis aged at 1-12 months (67 males and 49 females). Fifty healthy infants at similar age were employed as normal controls. The serum 25(OH)D3 levels in the children with mild (27.30 ± 5.98 ng/ml) and severe (24.40 ± 6.27 ng/ml) pertussis were significantly lower than that in the healthy group (30.16 ± 5.13 ng/ml; p <0.01). The vitamin D deficiency rates in children with mild (55.9%) and severe (78.12%) pertussis were significantly higher than that in the control group (34%; p < 0.01). The serum levels of LL-37 and HBD-2 were significantly higher in pertussis patients. Spearman rank correlation analysis did not show any correlation of 25-(OH)D3 with LL-37 or HBD-2. Most children with pertussis had vitamin D deficiency accompanied by elevated serum LL-37 and HBD-2 levels. However, the average level of 25(OH)D3 at 26.50 ng/ml in the infants with pertussis may not affect the immuno-regulatory ability; thus, the infants with pertussis still maintained a higher level of AMPs (LL-37 and HBD-2) against pertussis infection.