section_path: Mononuclear cells of skeletal muscle
section_name: Mononuclear cells of skeletal muscle
paragraph_text: Mononuclear cells of skeletal muscle
  
  Nuclei present in skeletal muscle are about 50% myocyte nuclei and 50% mononuclear cell nuclei. Mononuclear cells found in skeletal muscle tissue samples from mice and humans can be identified by messenger RNA transcription of cell type markers. Cameron et al. identified nine cell types. They include endothelial cells that line capillaries (45% of cells), fibro-adipogenic progenitors (FAPs)(20%), pericytes (14%) and endothelial-like pericytes (4%). Another 9% of mononuclear cells are muscle stem cells, adjacent to muscle fiber cells. Types of lymphoid cells (such as B-cells and T-cells) (3%) and myeloid cells such as macrophages (2%) made up most of the remaining mononuclear cells of skeletal muscle. In addition, Cameron et al. also identified two types of myocyte cells, Type I and Type II. Each of the different types of cells in skeletal muscle was found to express different sets of genes. The median number of genes expressed in each of the nine different cell types was 1,331 genes. When a biopsy is taken from a thigh muscle, however, the biopsy contains all the different cell types. Mixed together, in a biopsy of human thigh skeletal muscle, there are 13,026 to 13,108 genes with detected expression.