Immunological Functions of the Omentum

The omentum is a dynamic visceral adipose organ that extends across the peritoneal cavity and houses specialised immune structures known as milky spots or fat-associated lymphoid clusters (FALCs). These discrete nodules comprise stromal cells, mesothelial cover cells and diverse immune populations including macrophages, B1 and B2 lymphocytes, innate lymphoid cells and neutrophils. Under homeostatic conditions, the omentum surveys peritoneal fluid, captures antigens and orchestrates lymphocyte trafficking. In response to infection or sterile inflammation, omental stromal niches rapidly recruit circulating neutrophils and monocytes, promote germinal centre reactions and support long-term memory. Beyond host defence, the omentum contributes to tissue repair through secretion of growth factors and regulation of angiogenesis, and modulates systemic metabolism by fostering immune–adipocyte crosstalk. Collectively, these functions position the omentum as a sentinel of the abdominal cavity, integrating innate and adaptive immunity with tissue homeostasis.

Research from Nature Portfolio

Recent work has revealed that specialised high endothelial venules (HEVs) within omental milky spots serve as a principal gateway for neutrophils during acute peritonitis. These venules express unique adhesion ligands that permit rapid neutrophil transendothelial migration, outpacing entry via conventional postcapillary venules. Upon bacterial challenge, neutrophils and resident macrophages converge within milky spots to capture and neutralise pathogens, thereby preventing systemic spread and sepsis. Disruption of this pathway markedly exacerbates peritoneal infection, emphasising the clinical relevance of omental HEVs as targets for modulating early host defence in septic peritonitis.

Immunological Functions of the Omentum publication trend

The graph below shows the total number of articles in immunological functions of the omentum across all publications each year (not limited to Nature Index journals).

Technical terms

Milky spots: Discrete lymphoid-like structures in the omentum that capture peritoneal antigens and facilitate immune cell interactions.

High endothelial venules (HEVs): Specialised blood vessels lined by plump endothelial cells that enable efficient leukocyte trafficking into lymphoid tissues.

Fat-associated lymphoid clusters (FALCs): Ectopic immune aggregates within adipose depots that support innate surveillance and adaptive responses.

Fibroblastic reticular cells: Stromal cells that produce chemokines and extracellular matrix components to organise lymphoid microenvironments and guide lymphocyte migration.

References

1. Aldh1a2 + fibroblastic reticular cells regulate lymphocyte recruitment in omental milky spots. Journal of Experimental Medicine (2023).
2. Development and organization of omental milky spots. Immunological Reviews (2024).
3. Protection from septic peritonitis by rapid neutrophil recruitment through omental high endothelial venules. Nature Communications (2016).
4. Fat-Associated Lymphoid Clusters in Inflammation and Immunity. Frontiers in Immunology (2016).
5. Fat‐associated lymphoid clusters: Supporting visceral adipose tissue B cell function in immunity and metabolism. Immunological Reviews (2024).