Biomarkers in diagnosis of allergic rhinitis
With deeper insights into mechanisms of AR, novel biomarkers have recently been identified in its diagnosis. Furthermore, several immune cells and mediators, genes and metabolites have been studied to explore their potential utilization in diagnosis of AR.
Immune cells andmediators
Several potential immune cells (granulocytes, lymphocytes, etc.) and mediators might serve as diagnostic biomarkers of AR.14,76 Izuhara and colleagues have reported that induction and increased expression of periostin reflect type 2 inflammation and remodelling, and could be regarded as an emerging biomarker for allergic diseases.77 One study has demonstrated that allergen-induced surface CD203c expression on basophils exhibits a time-of-day-dependent variation, and allergen-specific basophil reactivity shows daily variations depending on circadian clock activity in basophils, which could partly be responsible for temporal symptomatic variations in AR.78 One recent study has suggested that circulating group 2 innate lymphoid cells (ILC2s) may play an important role in the pathology of AR, particularly as increased levels of ILC2scorrelated with symptom scores and IL-13 levels in house dust mite (HDM)-sensitized AR patients,79 and these cells produce large amounts of proinflammatory mediators in response to Th2 cytokines.80,81 Indeed, a more recent study by Tojima and colleagues found that prostaglandin D2 (PGD2) and cysteinyl leukotriene (cysLTs) might induce ILC2s to produce Th2 cytokines such as IL-5 and IL-13.82 Similarly, ST2-expressing pathogenic memory T helper (Th) 2 cells, producing substantial amounts of IL-33-induced IL-5 and IL-13, have been shown to be linked to sensitization and the onset and progression of AR (Figure 3).83