Goblet cell numbers were reduced in Il6−/− mice and MUC5AC expression was reduced upon AF exposure versus controlsIL6 directly induced IL13 production on CD4+ T cells and was essential for mucus productionIL6 and IL21 deficiency resulted in IgE hypersecretion and increased IgE during allergic inflammation. IL6 contributed to IgG1 productionIL6 deficiency impaired IL17 production in induced allergic inflammationIL6 was rapidly produced in the lung upon allergen exposure and played a key role in dictating immune response against allergens. This evidence concerns the gene CD4 and atrial fibrillation.