Immunohistochemical Identification of Human Skeletal Muscle Macrophages
Kate Kosmac,
Bailey Peck,
R. Walton,
Jyothi Mula,
Philip Kern,
Marcas Bamman,
Richard Dennis,
Cale Jacobs,
Christian Lattermann,
Darren Johnson,
Charlotte Peterson
Affiliations
Kate Kosmac
Department of Rehabilitation Sciences, College of Health Sciences and Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
Bailey Peck
Department of Rehabilitation Sciences, College of Health Sciences and Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
R. Walton
Department of Rehabilitation Sciences, College of Health Sciences and Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
Jyothi Mula
Center for Genetic Muscle Disorders, Kennedy Krieger Institute, Baltimore, MD, USA
Philip Kern
Department of Internal Medicine, Division of Endocrinology and Center for Clinical and Translational Sciences, University of Kentucky, Lexington, KY, USA
Marcas Bamman
Center for Exercise Medicine and Department of Cell, Developmental, and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL, USA
Richard Dennis
Geriatric Research Education and Clinical Center, Central Arkansas Veterans Healthcare System, Little Rock, AR, USA
Cale Jacobs
Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky, Lexington, KY, USA
Christian Lattermann
Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky, Lexington, KY, USA
Darren Johnson
Department of Orthopaedic Surgery and Sports Medicine, University of Kentucky, Lexington, KY, USA
Charlotte Peterson
Department of Rehabilitation Sciences, College of Health Sciences and Center for Muscle Biology, University of Kentucky, Lexington, KY, USA
Macrophages have well-characterized roles in skeletal muscle repair and regeneration. Relatively little is known regarding the role of resident macrophages in skeletal muscle homeostasis, extracellular matrix remodeling, growth, metabolism and adaptation to various stimuli including exercise and training. Despite speculation into macrophage contributions during these processes, studies characterizing macrophages in non-injured muscle are limited and methods used to identify macrophages vary. A standardized method for the identification of human resident skeletal muscle macrophages will aide in the characterization of these immune cells and allow for the comparison of results across studies. Here, we present an immunohistochemistry (IHC) protocol, validated by flow cytometry, to distinctly identify resident human skeletal muscle macrophage populations. We show that CD11b and CD206 double IHC effectively identifies macrophages in human skeletal muscle. Furthermore, the majority of macrophages in non-injured human skeletal muscle show a ‘mixed’ M1/M2 phenotype, expressing CD11b, CD14, CD68, CD86 and CD206. A relatively small population of CD11b+/CD206- macrophages are present in resting skeletal muscle. Changes in the relative abundance of this population may reflect important changes in the skeletal muscle environment. CD11b and CD206 IHC in muscle also reveals distinct morphological features of macrophages that may be related to the functional status of these cells.
