Nonprofessional antigen presenting cell is A/E –
**Core Concept**
The question is about non-professional antigen presenting cells (APCs), which are cells that can present antigens to T-cells but are not part of the conventional immune system's APC lineage. These cells play a crucial role in bridging the innate and adaptive immune responses.
**Why the Correct Answer is Right**
Non-professional APCs, such as epithelial cells, endothelial cells, and fibroblasts, can engulf and process antigens through phagocytosis or receptor-mediated endocytosis. They then display antigenic peptides on their surface via MHC class I molecules, which can be recognized by CD8+ T-cells. This process is essential for initiating an immune response against pathogens or tumors. In contrast, professional APCs like dendritic cells and macrophages are highly specialized for antigen processing and presentation.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because, while epithelial cells can function as non-professional APCs, they are not the only example.
**Option B:** This option is incorrect because endothelial cells can also present antigens, but this is not the only function of non-professional APCs.
**Option C:** This option is incorrect because fibroblasts can also act as non-professional APCs, but this is not the correct answer choice.
**Option D:** This option is incorrect because it is not a correct example of a non-professional APC.
**Clinical Pearl / High-Yield Fact**
Non-professional APCs can contribute to the development of autoimmune diseases by presenting self-antigens to T-cells, leading to immune activation and tissue damage.
**Correct Answer: B. Endothelial cells.**