Complex sentence: Mast cells are a type of innate immune cell that resides in the connective tissue and in the mucous membranes, and are intimately associated with defense against pathogens, wound healing, but are also often associated with allergy and anaphylaxis.
Split into simpler sentences: Mast cells are a type of innate immune cell that reside in connective tissue and in the mucous membranes. They are intimately associated with defense against pathogens and wound healing, but are also often associated with allergy and anaphylaxis.