Blood monocytes in cystic fibrosis

Background: Neutrophilic inflammation causes lung damage in cystic fibrosis (CF). Recent data from animal models and other chronic pulmonary inflammatory conditions suggest that the monocytes/macrophages may be an important driver of airway inflammation. CF may be associated with increased airway levels of chemoattractants for monocytes and resulting expansion of CD14++ small macrophages. I sought to assess the levels of monocyte chemoattractants CCL2 and CX3CL1 in the blood and airways of CF patients, and expression of their respective receptors CCR2 and CX3CR1 on monocytes. In a pilot study, I sought evidence for expansion of airway CD14++ small macrophages. Methods: Blood was obtained from 32 CF patients and 25 healthy controls; and induced sputum (IS) from 24 CF patients and 17 healthy controls. Flow cytometry was used to determine expression of CCR2 and CX3CR1 on CD14++ and CD14+CD16+ blood monocytes and to characterise IS airway macrophages. CCL2 and CX3CL1 levels in blood and IS were determined by ELISA. Results: Absolute count of total monocytes and monocytes subpopulations was not different between CF and controls. Serum CCL2, but not CX3CL1, was increased in CF patients (p=0.006). Similarly, CF was associated with increased IS CCL2, but not CX3CL1 (190.6 vs. 77.3 pg/mL; p=0.029). CCR2 was expressed on CD14++ monocytes but not on CD14+CD16+ monocytes. Both CD14+CD16+ and CD14++ cells expressed CX3CR1 but the expression was higher in CD14+CD16+ cells compared to the CD14++ cells. There was no difference in expression of both chemokine receptors by either monocyte subpopulation between CF and controls. Small macrophages were significantly increased in CF airways (p=0.018). Conclusion: CCL2, but not CX3CL1 is increased in the airway and blood of CF patients. Blood monocytes from CF patients are phenotypically competent to respond to CCL2, since they express normal levels of CCR2. Preliminary results suggest an expansion of small macrophages in CF airways.