Adipose tissue macrophages: phenotypic plasticity and diversity in lean and obese statesMorris, David La; Singer, Kanakadurgaa; Lumeng, Carey Na,bCurrent Opinion in Clinical Nutrition & Metabolic Care: July 2011 - Volume 14 - Issue 4 - p 341–346 doi: 10.1097/MCO.0b013e328347970b Genes and cell metabolism: Edited by Nada Abumrad Abstract Author Information Purpose of review Proinflammatory adipose tissue macrophages (ATMs) contribute to obesity-associated disease morbidity. We will provide an update of the current state of knowledge regarding the phenotypic and functional diversity of ATMs in lean and obese mice and humans. Recent findings The phenotypic diversity of ATMs is now known to include more than two types requiring an expansion of the simple concept of an M2 to M1 shift with obesity. Potential functions for ATMs now include the regulation of fibrosis and response to acute lipolysis in states of caloric restriction. Novel pathways that can potentiate ATM action have been identified, which include inflammasome activation and the response to lipodystrophic adipose tissue. Studies provide a new appreciation for the ability of ATMs to respond dynamically to the adipose tissue microenvironment. Summary ATMs play a key role in shaping the inflammatory milieu within adipose tissue, and it is now apparent that ATM heterogeneity is acutely shaped by the adipose tissue environment. To account for the new findings, we propose a new nomenclature for ATM subtypes that takes into account their diversity. aDepartment of Pediatrics and Communicable Diseases, USA bDepartment of Molecular and Integrative Physiology, University of Michigan Medical School, University of Michigan, Ann Arbor, Michigan, USA Correspondence to Carey N. Lumeng, MD, PhD, 4520B Medical Science Research Building 1, 1150 West Medical Center Drive, Ann Arbor, MI 48109-5652, USA Tel: +1 734 936 4200; e-mail: firstname.lastname@example.org © 2011 Lippincott Williams & Wilkins, Inc.