Paracrine Provision of Lipids in the Immune System
Caroline M. Pond
Affiliation: Department of Life Sciences, The Open University, Milton Keynes, MK7 6AA, UK.
Keywords: HIV-associated adipose redistribution syndrome, adipose tissue, perinodal adipocytes, lymph nodes, dendritic cells, nutrition, Crohn's disease
Adipocytes enclosing lymph nodes (and omental milky spots) are specialized for paracrine interactions with lymphoid cells. They secrete and respond to cytokines and their lipids contain more polyunsaturated fatty acids, precursors of eicosanoids and docosanoids. Dendritic cells and lymph node lymphoid cells obtain many, possibly all, fatty acids found in structural lipids from adjacent perinodal adipocytes. By supplying appropriate fatty acids to lymph nodes and dendritic cells, perinodal adipocytes intervene between the diet and the immune systems nutrition and partially emancipate it from fluctuations in abundance and composition of dietary lipids. Site-specific differences in the composition of lipids taken up from contiguous adipocytes create further dendritic cell diversity. Local immune stimulation induces the formation of more adipocytes, which may contribute to mesenteric and omental hypertrophy in chronic inflammatory diseases such as HIV-infection. Perinodal adipose tissue is abnormal in Crohns disease, leading to insufficient fatty acid precursors of eicosanoids in mesenteric lymph nodes, even when they are plentiful in the diet. Perivascular, epicardial and perinodal adipose tissue have some common properties. Adipose tissue partitioned into many depots, some specialised for paracrine interactions, is a fundamental feature of mammals, underpinning multiple simultaneous responses to pathogens and more efficient utilization of lipids.
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