IgA secretion is seen in –
**Core Concept**
IgA secretion is a key aspect of mucosal immunity, playing a crucial role in protecting the body's mucosal surfaces from pathogens. IgA antibodies are predominantly secreted in a dimeric form, providing a robust defense mechanism against invading microorganisms.
**Why the Correct Answer is Right**
IgA secretion is primarily facilitated by the J-chain, a polypeptide that links two IgA molecules together, allowing them to be secreted across mucosal epithelial cells. This process is mediated by the polymeric Ig receptor (pIgR), also known as secretory component (SC), which binds to the J-chain and facilitates the transcytosis of IgA through the epithelial cells. This results in the secretion of dimeric IgA antibodies into mucosal secretions, such as saliva, tears, and mucus.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe the primary mechanism of IgA secretion.
**Option B:** This option is incorrect as it is not directly related to IgA secretion.
**Option C:** This option is incorrect as it is not a known mechanism of IgA secretion.
**Clinical Pearl / High-Yield Fact**
The polymeric Ig receptor (pIgR) is a key molecule involved in the transcytosis of IgA antibodies across mucosal epithelial cells. Defects in this receptor can lead to impaired mucosal immunity and increased susceptibility to infections.
**Correct Answer:** D.