 Acute inflammation of the lung (usually caused in response to pneumonia) does not cause pain unless the inflammation involves the parietal pleura, which does have pain-sensitive nerve endings.The process of acute inflammation is initiated by resident immune cells already present in the involved tissue, mainly resident macrophages, dendritic cells, histiocytes, Kupffer cells and mast cells.These cells possess surface receptors known as "pattern recognition receptors" (PRRs), which recognize (i.e., bind) two subclasses of molecules