White blood cells help our bodies ward off invasions from microorganisms, but they serve other purposes too. Once white blood cell in particular, the “eosinophil” helps us when we are infected by multicellular parasites (worms and the like). Eosinophils, however, also play a more unpleasant role, and that is in allergies. When we suffer from allergies, eosinophils multiply and move to our lungs and other places, where they mediate inflammation and tissue damage. Thus eosinophils are the white blood cells we all love to hate.
However, researchers at the University of California, San Francisco (UCSF) have generated new data that, in their view, suggests that eosinophils also play an integral role in muscle regeneration.
Ajay Chawla, Associate Professor at the Cardiovascular Research Institute at UCSF and
lead researcher for this study, said, “Eosinophils are needed for the rapid clearance of necrotic debris, a process that is necessary for timely and complete regeneration of tissues.”
Chawla’s laboratory showed that eosinophils serve double duty when it comes to muscle repair. First, they remove the cellular debris that results from damaged tissues. Secondly, eosinophils secrete a protein called “Interleukin 4” or IL-4. IL-4 triggers a specific type of stem cell to replicate and repair muscle tissue.
According to Chawla, “Without eosinophils you cannot regenerate muscle.”
These eosinophil-activated stem cells are known as “fibro/adipogenic progenitors” (FAP). Until recently, the general thinking surrounding FAPs was that they could only form fat tissue (see Natarajan A., Lemos DR, and Rossi FM, Cell Cycle 2010 9(11): 2045-6). However, when FAPs are exposed to IL-4, they begin to differentiate into muscle fibers.
“They wake up the cells in muscle that divide and form muscle fibers,” said Chawla
“Bites from venomous animals, many toxicants, and parasitic worms all trigger somewhat similar immune responses that cause injury. We want to know if eosinophils and FAPs are universally employed in these situations as a way to get rid of debris without triggering severe reactions such as anaphylactic shock,” said Chawla.