Circulating white blood cells and lung function impairment: the observational studies and Mendelian randomization analysis

BACKGROUND: Circulating white blood cell (WBC) counts have been related to lung function impairment, but causal relationship was not established. We aimed to evaluate independent effects and causal relationships of WBC subtypes with lung function. METHODS: The 19,159 participants from NHANES 2011–2012 (n = 3570), coke-oven workers (COW, n = 1762) and Dongfeng-Tongji (DFTJ, n = 13,827) cohorts were included in the observational studies. The associations between circulating counts of WBC subtypes and prebronchodilator lung function were evaluated by linear regression models and LASSO regression was used to select effective WBC subtypes. Summary statistics for WBC-associated SNPs were extracted from literature, and Mendelian randomization (MR) analysis with inverse-variance weighted (IVW) method was applied to estimate the causal effects of total WBC and subtypes on lung function among 4012 subjects from COW (n = 1126) and DFTJ cohorts (n = 2886). RESULTS: Total WBC counts were negatively associated with lung function among three populations and their pooled analysis indicated that per 1 × 10(9) cells/L increase in total WBC was associated with 36.13 (95% CI: 30.35, 41.91) mL and 25.23 (95% CI: 19.97, 30.50) mL decrease in FVC and FEV(1), respectively. Independent associations with lung function were found for neutrophils, monocytes, eosinophils and basophils (all p < .05), except lymphocytes. Besides, IVW MR analysis showed that genetically predicted total WBC and neutrophil counts were associated with reduced FVC (p = .017 and .021, respectively) and FEV(1) (p = .048 and .043, respectively). CONCLUSIONS: WBC subtypes were independently associated with lower lung function except lymphocytes. Our findings suggest that circulating neutrophils may be causal factors in lung function impairment. KEY MESSAGES: White blood cell (WBC) subtypes were negatively associated with lung function level except lymphocytes in the observational studies. Associations of WBC subtypes with lung function may be modified by sex and smoking. Mendelian randomization analysis shows that neutrophils may be causal factors in lung function impairment.