28 demonstrated that azithromycin treatment results in the reduction in IL-17-positive cells in the lung biopsies of lung transplant recipients with lymphocytic bronchiolitis/ARAD and not in PAN. Activation of IL-17 T cells and stimulation of IL-17 expression in neutrophils may be triggered by some intracellular bacteria 31 and viruses 32, which may be difficult to detect using standard microbiological methods. Here, IL17A is linked to polyarteritis nodosa.