Structural relationships between immune cells and longitudinal muscle during a Trichinella spiralis infection in the rat intestine

A Trichinella spiralis infection produces an acute inflammatory reaction and tissue damage in the mucosa, and, in addition, functional changes occur in the external muscle layers. The aim of the present study was to characterize structural changes in the musculature that occur during early infection, and to identify relationships between immune cells and muscle cells, as part of an ongoing investigation into the immune modulation of motor function in the gut. Rats were infected with T. spiralis larvae and the gut fixed at 12 h, 24 h, 48 h and 6 days post-infection for electron microscopy of the longitudinal muscle. Macrophages and lymphocytes penetrated the longitudinal musculature 12-24 h post-infection. Distinct contacts were observed between specific cell types; cellular protrusions from macrophages or lymphocytes made close apposition contacts with smooth muscle cells. Resident macrophages in the subserosal space, fibroblast-like cells as well as smooth muscle cells showed marked activation during inflammation. Fibroblast-like cells were frequently seen intercalated between lymphocytes and smooth muscle cells, hence they may mediate communication between immune cells and the musculature.