Fat-associated lymphoid clusters: Supporting visceral adipose tissue B cell function in immunity and metabolism

Aortic, musculoskeletal and organ characteristics on computed tomography in knee osteoarthritis - an explorative study in the IMI-APPROACH cohort

The systemic associations with knee osteoarthritis (KOA) are incompletely understood. This study explores aortic disease, musculoskeletal and organ findings in patients with KOA in relation to their symptoms or radiographic abnormalities. Full body computed tomography (CT) scans of 255 IMI-APPROACH participants were investigated using an automated analysis of multislice CT (Voronoi Health Analytics) that extracts aortic size and calcifications, and volumes and densities of bones, muscles, fat compartments and thoracic and abdominal organs. The CT measurements were primarily related to KOA as measured with Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), visual scores and automated knee radiograph analysis of osteophytes, bone sclerosis and joint space width. The median age was 67 years, body mass index (BMI) 26.8 kg/m2 and 78% were female. About half had Kellgren-Lawrence grade ≥ 2. Larger knee osteophyte area was associated with a larger aortic volume (RSpearman=0.21,P = 0.001), which can be due to elongation or dilatation. We observed an association between more symptoms and increased psoas (RSpearman=-0.23,P < 0.001) and lower leg (RSpearman=-0.23,P < 0.001) muscle density, suggesting less microscopic muscle fat. Symptomatic KOA was associated with substantially lower lung volume (771 ml difference between 50% worst and 50% best WOMAC), but not with visible lung disease. Lung volume and density were significantly associated with the physical functioning WOMAC component. These associations remained significant after adjustment for age, sex and BMI. KOA is associated with significant systemic changes, including altered aortic and organ volumes. These correlations suggest that KOA's impact may extend beyond the joints. Future research should explore the causal relationships and therapeutic implications associations.

Immunity in adipose tissues: Cutting through the fat

Well known functions of adipose tissue include energy storage, regulation of thermogenesis, and glucose homeostasis-each of which are associated with the metabolic functions of fat. However, adipose tissues also have important immune functions. In this issue of Immunological Reviews, we present a series of articles that highlight the immune functions of adipose tissue, including the roles of specialized adipose-resident immune cells and fat-associated lymphoid structures. Importantly, immune cell functions in adipose tissues are often linked to the metabolic functions of adipocytes and vice versa. These reciprocal interactions and how they influence both immune and metabolic functions will be discussed in each article. In the first article, Wang et al.,11 discuss adipose-associated macrophages and how obesity and metabolism impact their phenotype and function. Several articles in this issue discuss T cells as either contributors to, or regulators of, inflammatory responses in adipose tissues. Valentine and Nikolajczyk12 provide insights into the role of T cells in obesity-associated inflammation and their contribution to metabolic dysfunction, whereas an article from Kallies and Vasanthakumar13 and another from Elkins and Li14 describe adipose-associated Tregs and how they help prevent inflammation and maintain metabolic homeostasis. Articles from Okabe35 as well as from Daley and Benezech15 discuss the structure and function of fat-associated lymphoid clusters (FALCs) that are prevalent in some adipose tissues and support local immune responses to pathogens, gut-derived microbes and fat-associated antigens. Finally, an article from Meher and McNamara16 describes how innate-like B1 cells in adipose tissues regulate cardiometabolic disease. Importantly, these articles highlight the physical and functional attributes of adipose tissues that are different between mice and humans, the metabolic and immune differences between various adipose depots in the body and the differences in immune cells, adipose tissues and metabolic functions between the sexes. At the end of this preface, we highlight how these differences are critically important for our understanding of anti-tumor immunity to cancers that metastasize to a specific example of visceral adipose tissue, the omentum. Together, these articles identify some unanswered mechanistic questions that will be important to address for a better understanding of immunity in adipose tissues.