Since the main producers of IL-6 are APCs and endothelial cells80, APC-derived IL-6 plays a critical role in restricting Th2 differentiation81 and several relevant types of APC were more abundant among VAP vs. HC (Fig. 2b), we investigated a potential correlation between serological IL-6 levels and specific circulating APC subsets or total APCs. This evidence concerns the gene IL6 and ventilator-associated pneumonia.