Hypersensitivity Reactions and the Respiratory System: Imaging Based Review

Hypersensitivity reactions are characterized by inappropriate response of the immune system to an inciting antigen, which results in damage to various body tissues. Respiratory system can be involved as a part of hypersensitivity reaction by a myriad of conditions ranging from infective pathologies like tuberculosis to non-infective processes such as asthma, graft- versus host disease, sarcoidosis and vasculitic disorders. Recognition of specific imaging features in appropriate clinical setting helps in diagnosing these conditions. We present a review of mechanism of different types of hypersensitivity reactions; and imaging features of various such pathological conditions affecting the respiratory system.