<prompt> The most impoant source of histamineMast cellsEosinophilNeutrophilsMacrophages  <response>: ref Robbins 8e p57,9e p83 Histamine is synthesized in all tissues, but is paicularly abundant in skin, lung and gastrointestinal tract. Mast cells, which are present in many tissues, are a prominentsource of histamine, but histamine is also secreted by a number of other immune cells. 