Th2 cells in rapid immune responses and protective avoidance reactions.

Type 2 helper cells (Th2 cells) differentiate from CD4 helper T cells under the influence of IL-4 and conventional or monocyte-derived CD11b+ dendritic cells. Th2 cells are capable of generating IL-4, IL-5, and IL-13, as well as evoking immunoglobulin class-switch to IgE. Three types of rapid immune responses are Th2 cell-dependent: (1) mast cell-IgE mediated allergic reactions, (2) Th2 cell-derived cytokine-mediated reactions that complement allergic reactions and protect the host from toxins, xenobiotics, environmental irritants, and helminthic parasites, and (3) IgE-stimulated mast cell-derived cysteinyl-leukotriene mediated avoidance of toxins. The contributions of Th2 cell-derived cytokines to eosinophilia (IL-5), IgE class-switch, and epithelial barrier activation, mucous secretion, and metaplasia (IL-4 and IL-13) in asthma, allergic rhinitis with polyps and atopic dermatitis have led to anti-cytokine monoclonal antibody treatments. Anti-IL-5 neutralizing monoclonal antibody in asthma and anti-IL-4/IL-13 receptor neutralizing monoclonal antibody in asthma and atopic dermatitis are proven successful therapies in appropriately selected patients who are not sufficiently improved by conventional treatments.