According to textbooks, type 2 helper T cells (Th2 cells) preside over asthma. T cells are a subset of the white blood cells known as lymphocytes, and the conventional view is that an asthma attack occurs when Th2 cells secrete a certain set of immune-signalling proteins called cytokines that inflame the lungs, irritate the chest and cause asthmas characteristic wheezing. However, another cytokine, interleukin-17 (IL-17), which does not belong to Th2's signature set, has been caught lurking in lung tissue, sputum and the blood of asthmatic patients (see 'New partner in crime?'.) "We thought we understood asthma, but now we know it's much more complex," reflects immunologist Manfred Kopf at the Swiss Federal Institute of Technology in Zurich.
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