Gastrointestinal tract, specific immune response

The immune system is characterized by a unique distribution, and many of its components are located close to the principal sites of absorption, including the gastrointestinal tract, the pulmonary tract, and the skin. Therefore, the immune system is in a position to be exposed to potentially high concentrations of drugs and chemicals. This phenomenon is especially important in hypersensitivity responses where the primary portal of entry of the hapten can determine the specific site of the reaction. 

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