CD4 and childhood onset asthma: Furthermore, IL-2 can modulate the differentiation of CD4+ T helper (Th) cell subsets, including T-helper 1 (Th1), T-helper 2 (Th2), T-helper 17 (Th17), and regulatory T (Treg) cells, the key pathways in allergic and non-allergic inflammation and childhood asthma [49, 50].