Recruitment of mast cells to muscle after mild damage.

We followed the response of muscle following mild intentional injury to determine a temporal sequence of cellular events involved in muscle repair. We found that intramuscular saline injection induced mild damage to muscle which resulted in the gradual recruitment of mast cells. Around the needle track, mast cells appear around 8 h post-injection. Mast cell accumulation were most dramatic immediately neighboring the posterior tibial vessels supplying the injured muscle. Dystrophin-deficient mdx muscle showed mast cell accumulations 3-fold higher than normal muscle, and this number did not change after saline injection. Additionally, we show that stem cell factor (SCF), a known mast cell chemoattractant, is expressed in both normal and mdx muscle at high levels. This steady-state level did not appear to be influenced by injury or dystrophin status. The implications of these findings are discussed as they relate to the repair of injured muscle and to their possible significance in the pathophysiology of Duchenne muscular dystrophy.