Hypersensitivity pneumonitis

Hypersensitivity refers to an abnormal and excessive immune reaction, and pneumonitis refers to an inflammation of the lungs.

So, hypersensitivity pneumonitis is when a person’s immune system reacts excessively to something that’s inhaled, causing lung inflammation.

The lungs are made up of a collection of branching tubes called bronchioles that get smaller and smaller until they end in little air-filled sacs called alveoli.

The alveoli are like clusters of grapes, and they’re covered by nets of tiny capillaries - and that’s where gas exchange occurs.

Between the airways and the blood vessels there’s lung tissue - called interstitium, which is full of proteins and structural cells .

Hypersensitivity pneumonitis can be caused by a variety of organic antigens, from coffee bean dust, to moldy sugarcane, to bacterial spores in the mist from hot tubs. The resulting disease is often named for the profession at risk.

For instance, the most common type is Farmer’s lung, which is caused by breathing in the spores of actinomycetes that live in moist, newly harvested hay.

Sugarcane farmers might also get bagassosis, from inhaling actinomycete spores in moldy bagasse, or sugarcane fiber.

Malt worker’s lung is from Aspergillus spores from moldy barley.

Humidifier or air conditioner lung is caused by inhaling the spores of actinomycetes that grow in the warm water reservoirs of these machines.

Pigeon breeders lung is caused by breathing in proteins from bird poop or feathers, but other animal proteins, such as those from fur, can also cause the disease.

When a person inhales an organic antigen, it travels down the trachea, into the bronchi and ends up in the lungs where they settle in the alveolus. There, it gets picked up by an alveolar macrophage which takes it to the nearest lymph node,