The immune system faces the arduous task of defending the mucosal surfaces from invading
pathogens, but must simultaneously repress responses against commensal organisms and
other inert antigens that are abundant in the external environment, as inappropriate immune
activation might expose the host to increased risk of autoimmunity. The behavior of
individual immune cells is governed by the expression of transcription factors that are
responsible for switching immune response genes on and off. T-bet (T-box expressed in T …