Hypersensitivity pneumonitis is/are caused by –
**Core Concept**
Hypersensitivity pneumonitis is a type of lung disease characterized by an immune-mediated inflammatory response to inhaled antigens, leading to lung injury and fibrosis. This condition is often associated with exposure to organic dusts, such as farming, bird breeding, or certain chemicals.
**Why the Correct Answer is Right**
The condition arises when the immune system overreacts to the inhaled substance, triggering an inflammatory response that damages the lung tissue. This response is mediated by T-lymphocytes and the release of cytokines, which attract macrophages and other inflammatory cells to the affected area. The inflammation can lead to the formation of granulomas, which are characteristic of hypersensitivity pneumonitis.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify a known cause of hypersensitivity pneumonitis.
**Option B:** This option is incorrect as it is not a recognized antigen associated with hypersensitivity pneumonitis.
**Option C:** This option is incorrect as it is a different type of lung disease, characterized by inflammation of the airways.
**Clinical Pearl / High-Yield Fact**
Hypersensitivity pneumonitis can be prevented by avoiding exposure to the offending antigen, and treatment involves corticosteroids and immunosuppressive agents to reduce inflammation and prevent further lung damage.
**Correct Answer:** D. Bird proteins, moldy hay, and other organic dusts are common causes of hypersensitivity pneumonitis.