MUC5AC and respiratory system disorder: Type II gastric mucin contains mucin 2 and mucin 6 (MUC2/MUC6), as well MUC5AC [24,25,26], and although these are not the major secreted mucins in saliva [27,28], they are gel-forming and serve as a surrogate for the secretory gel-forming mucins in saliva upregulated during respiratory disease.