The role played by Major Histocompatibility Complex (MHC)-1 and -2 is to:(AlIMS November 2014, November 2013)
**Core Concept**
The Major Histocompatibility Complex (MHC) plays a crucial role in the immune system by presenting peptide fragments from inside the cell to the T-cells, thereby initiating an immune response. This process involves the presentation of antigens to CD4+ and CD8+ T-cells.
**Why the Correct Answer is Right**
MHC-1 molecules are expressed on the surface of all nucleated cells and present endogenously synthesized antigens to CD8+ T-cells, also known as cytotoxic T-cells. This is a critical step in the elimination of infected cells and tumor cells. On the other hand, MHC-2 molecules are primarily expressed on the surface of antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B-cells, and present exogenously acquired antigens to CD4+ T-cells, which play a key role in activating the immune response.
**Why Each Wrong Option is Incorrect**
**Option A:** This option would imply a role for MHC-1 in presenting exogenously acquired antigens, which is incorrect as MHC-1 presents endogenously synthesized antigens.
**Option B:** This option suggests a role for MHC-2 in presenting antigens to CD8+ T-cells, which is incorrect as MHC-2 primarily presents antigens to CD4+ T-cells.
**Clinical Pearl / High-Yield Fact**
MHC molecules are essential for the proper functioning of the immune system, and any defects in MHC genes can lead to severe immunodeficiency. For example, individuals with MHC class II deficiency are prone to recurrent infections and autoimmune disorders.
**Correct Answer: C. Presenting antigens to CD4+ and CD8+ T-cells.**