Is Adipose Tissue an Immunological Organ?

Recently, several studies have reported endocrine properties in adipose tissues. The adipose tissue has also been reported to be associated with thermal insulation, mechanical protection, energy storage and release, immune responses, and nonshivering thermogenesis. In the present review, the authors attempted to understand the way in which the adipose tissue is associated with the initiation and modulation of both adaptive and innate immune responses. The information collected from the literature published to date suggests that in an obese individual, the adipose tissue undergoes inflammation. This process leads to insulin resistance, thereby causing various metabolic syndromes, including type 2 diabetes. Apart from the adipocytes, the adipose tissue is also reported to be comprised of a distinct set of immune cells. These immune cells are associated with both innate and adaptive immune responses. Additionally, immune-related structures, for instance, fat-related lymphoid clusters and lymph nodes, are also found in adipose tissues. These additional structures behave as a secondary lymphoid organ and are responsible for modulating the adaptive immune response. Thus, the adipose tissue serves as an active immunological organ and also has the capability of modulating the whole-body metabolism via endocrine and paracrine mechanisms. Nevertheless, it is still unclear if the immune cells present in the adipose tissue have a direct function in the host defense mechanisms. In the near future, unmasking the interactions among the adipocytes and leukocytes may enable us to identify clinically essential pathways that may help in controlling the adipose inflammation, which in turn, might help us manage various metabolic disorders.