Aggregated lymphoid nodules of ileum

Aggregated lymphoid nodules of ileum (Peyer's patches) are oval collections of lymphoid tissue located in the lamina propria and submucosa of the ileum, particularly along its antimesenteric border, with the greatest concentration in the terminal ileum. They are a characteristic anatomical feature used to distinguish the ileum from the jejunum.

Immune surveillance function of Payer's patches

The Payer's patches form an important component of the gut-associated lymphoid tissue (GALT) and serve as the primary immune surveillance sites of the small intestine. They consist mainly of B lymphocyte follicles with germinal centres, surrounded by T lymphocytes, dendritic cells, macrophages, and plasma cells. They are covered by specialised follicle-associated epithelium containing microfold (M) cells, which sample antigens, microorganisms, and other particles from the intestinal lumen and transport them to underlying immune cells. This process initiates mucosal immune responses and stimulates the production of secretory IgA, the principal antibody involved in intestinal immunity.

In addition to protecting against pathogens, Peyer's patches help maintain immune tolerance to dietary antigens and normal intestinal flora.

Clinical correlates

These aggregated lymphoid nodules of ileum may become enlarged in childhood, act as a lead point for intussusception, and can undergo inflammation and ulceration in typhoid fever, potentially causing intestinal haemorrhage or perforation of the terminal ileum.