A recently discovered class of immune cell may hold the key to new treatments for asthma – and explain why existing therapies sometimes fail.

Asthma occurs when immune cells go into overdrive and release inflammatory chemicals called cytokines. These cause excess production of mucus, which plugs up the lungs. The disease is generally associated with immune cells called T-helper 2 (TH2) cells and the cytokines they release, but their response alone is not enough to trigger asthma.

Natural killer T (NKT) cells produce some of the same cytokines as TH2s, but release them faster and in greater quantities (see Diagram). …