Q.35 MHC-II is expressed by which of the following?
(1) All nucleated cells
(2) Antigen presenting cells
(3) RBCs
(4) All leukocytes
MHC-II Expression on Antigen Presenting Cells: Immunology MCQ Solved
MHC class II (MHC-II) molecules are key for CD4+ T cell activation in adaptive immunity. This SEO article clarifies the correct answer for the multiple-choice question on MHC-II expression.
Correct Answer
The correct answer is (2) Antigen presenting cells. MHC-II is primarily expressed on professional APCs like dendritic cells, macrophages, and B cells, presenting exogenous antigens to CD4+ T helper cells [web: conversation context].
Role in Immune Response
MHC-II molecules bind peptides from engulfed pathogens in endosomal compartments and display them on the cell surface for T cell recognition. This triggers cytokine release and immune coordination, distinct from MHC-I’s endogenous antigen presentation.
Option Analysis
| Option | Description | Expresses MHC-II? |
|---|---|---|
| (1) All nucleated cells | Express MHC class I for endogenous antigens (e.g., virus-infected cells); MHC-II restricted to APCs. | No |
| (2) Antigen presenting cells | Dendritic cells, macrophages, B cells constitutively express MHC-II; activated endothelial cells may inducibly. | Yes |
| (3) RBCs | Anucleate, lack MHC molecules entirely; no antigen presentation role. | No |
| (4) All leukocytes | Includes neutrophils, NK cells (MHC-I only); only subset (APCs) express MHC-II. | No |
Biological Importance
MHC-II on APCs bridges innate and adaptive immunity, essential for autoimmune disease understanding (e.g., rheumatoid arthritis) and vaccine design. Critical for immunology, molecular biology studies in exams.
