... and chemicals that cause extrinsic allergic alveolitis. Farmer's lung, which results from repeated inhalation of heat-loving bacteria in mouldy hay, is a well-known example of this condition. Another example is humidifier lung; it occurs when contaminated humidifiers or air conditioners circulate antigens that are capable of causing a hypersensitivity reaction. The mechanisms of this condition are contained within the alveolar. When the invading soluble antigen is inhaled into the lungs it combines with circulating IgG antibodies. Complexes are formed that precipitate out of the serum and into the tissue of the alveolar membranes. The complexes activate compliment and cause the release of mediators that increase vasodilation and vasopermeability. The immune complex then in turn binds with the Fc receptors on the mast cells and other leukocytes, this creates the localised inflammation. Activated Fc receptors cause the mast cells to degranulate which causes increased fluid and protein release, bringing about phagocytosis and ...

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