• Postoperative ileus
• muscularis externa
• macrophage
• monocyte
• dendritic cell
• nitric oxide

In Gut, Farro et al and Pohl et al present new findings on the role of myeloid cells in postoperative ileus (POI).1 2

POI is a frequent consequence of abdominal surgery that can lead to costly delays in patient recovery.3 The failure of peristalsis reflects paralysis of the smooth muscles of the intestine and several studies have suggested that this is dependent on macrophages in the muscularis externa (ME) layer of the gut wall that produce nitric oxide (NO).4

The intestine contains one of the largest pools of macrophages in the body, the majority of which is located in the lamina propria (LP) of the mucosa, near the epithelium. However macrophages are also present between the longitudinal and circular muscle layers of the ME, where they are in close proximity to the myenteric plexus.5 6 Recent studies indicate that LP and ME macrophages are phenotypically and functionally distinct under steady-state conditions.6 In particular, ME macrophages appear to have specialised tissue protection functions, including the production of factors such as bone morphogenic protein-2 (BMP2) that promote neuronal growth. In return, β₂-adrenergic receptors on ME macrophages allow them to be sustained by sympathetic neurons and these two-way interactions are at least partly dependent on the local microbiota.6 …