Allergic asthma, also considered to be the classic TH2 lung disease [6], starts with the processing of inhaled antigens by dendritic cells, a subset of antigen‐presenting cells (APCs) in lung tissue, and their presentation to T lymphocytes (results in activation of T cells) via the interaction of their ligand, CD80 (B7‐1), and the receptor molecule CD28 on T cells. The gene discussed is CD80; the disease is lung disorder.