A gene family that plays a major role in asthma susceptibility has been identified. This gene family, located at chromosome 5q23-35, is called TIM (T cell transmembrane, immunoglobulin and mucin) or Tapr (T cell and Airway Phenotype Regulator) . The TIM family of genes is involved in allergic response, asthma, and transplant tolerance. It controls the development of airway hyperreactivity (and the T cell production of interleukin 4 and 13). TIM-1 is also the receptor of the hepatitis A virus. This may explain the fact that hepatitis A virus infection decreases the chance asthma will develop.