MACROPHAGES AND DENDRITIC CELLS IN NORMAL AND REGENERATING MURINE SKELETAL-MUSCLE

Mononuclear phagocytes and MHC class II+ dendritic cells (DC) were ide ntified in frozen sections of skeletal muscle using a panel of pan-spe cific antimacrophage (MOMA-2, SER-4, Mac-1, F4/80), anti-major histoco mpatibility complex (MHC) class II (M5/114) and anti-DC (NLDC-145, N41 8, M342) monoclonal antibodies. Uninjured and regenerating skeletal mu scle were investigated in SJL/J and BALB/c mice, strains with known di fferences in muscle regenerative capacity. Resident tissue macrophages and MHC class II+ DC were present within uninjured mouse muscle. A su bpopulation of DC were positive for the pan-DC markers, N418 and M342, and negative for the lymphoid DC marker NLDC-145. Following crush inj ury, the macrophage population increased by day 2, became marked by da y 3, and had decreased by day 6. In contrast, the number of MHC class II+ cells around the injury site increased steadily after injury and r emained high at day 6. The numbers of macrophages and DC detected by i mmunohistochemical staining were consistently higher in SJL/J than BAL B/c muscles. This study confirms that macrophages are a significant co mponent of normal murine skeletal muscle and that these cells increase dramatically after injury. Furthermore the data also reveal for the f irst time that DC are present in normal skeletal muscle and that MHC c lass II+ cells, including DC, increase after injury. The presence of D C in muscle has important implications for the understanding of the im munobiology of muscle and immune-mediated processes such as the host v ersus graft responses following muscle transplants and autoimmune dise ases affecting this tissue. (C) 1997 John Wiley & Sons, Inc.