Allergic CRSwNP patients had decreased numbers of IL-21 producing Th17 cells compared to non-allergic CRSwNP (1.69 ± 0.57 vs. 9.41 ± 3.23) per mg of tissue respectively, Kruskal-Wallis p < 0.05 (Figure 5). Here, IL21 is linked to chronic rhinosinusitis with nasal polyps.