Both can trigger hyperreactivity of T cells and neutrophils.14 T lymphocytes respond to viral and bacterial infections, tending to a Th1 and Th17 response pattern, which in turn produces proinflammatory mediators such as IL-2, IL-6, IL-8, IL-12, IL- 18, IL-21, TNF-α and IFN-γ.7 It is worth outlining how some of these are related to BD:. The gene discussed is IL21; the disease is bacterial infectious disease.