Which of the following hypersensitivity reactions occurs in Farmer&;s lungs –
**Core Concept**
The question is testing the understanding of **hypersensitivity reactions**, specifically in the context of an occupational disease known as Farmer's lung. This condition is an example of a **type III hypersensitivity reaction**, which involves the formation of immune complexes.
**Why the Correct Answer is Right**
Given that Farmer's lung is a type of **hypersensitivity pneumonitis**, it is caused by the inhalation of antigens from moldy hay or other agricultural products, leading to an immune response. The correct answer is related to this type of reaction, which typically involves the deposition of immune complexes in the lungs, triggering an inflammatory response mediated by **complement** and **neutrophils**.
**Why Each Wrong Option is Incorrect**
**Option A:** This choice is incorrect because it does not correspond to the type of hypersensitivity reaction associated with Farmer's lung.
**Option B:** Similarly, this option is not related to the pathophysiology of Farmer's lung.
**Option C:** This choice is also incorrect as it does not accurately describe the hypersensitivity reaction in Farmer's lung.
**Option D:** Although not specified, any option not corresponding to a type III hypersensitivity reaction would be incorrect in this context.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that **hypersensitivity pneumonitis**, like Farmer's lung, is an occupational disease that can be prevented by avoiding exposure to the offending antigen, highlighting the importance of **personal protective equipment** in high-risk occupations.
**Correct Answer:** D. Type III hypersensitivity reaction.