IL17A and hypersensitivity pneumonitis: γδ T cells are also a well-known source of IL17A in response to antigen and bacterial infection, and other studies have also shown that in B. subtilis and Pigeon Droppings Extract induced model of HP, IL17A concentration was significantly increased in the lung and Vγ6Vδ1 or Vγ4 γδ expressing T cells are the predominant population of IL17A producing cells39,40.