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Difference Between MHC Class 1 and MHC Class 2 Proteins

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Difference Between Mhc Class 1 and Mhc Class 2 Proteins: The MHC (Major Histocompatibility Complex) proteins play a crucial role in the immune system by presenting antigens to the immune cells. Both MHC I and MHC II are responsible for distinguishing between self and non-self molecules, allowing the immune system to recognize and eliminate foreign invaders.

MHC Class I proteins are found on the surface of almost all nucleated cells in the body. MHC Class II proteins are primarily expressed on antigen-presenting cells, including dendritic cells, macrophages, and B cells. In this article, we will read about Major Histocompatibility Complex (MHC) proteins and the difference between MHC Class 1 and MHC Class 2 proteins.

MHC Class I Proteins

The MHC Class I proteins, also known as Major Histocompatibility Complex Class I proteins, are crucial components of the immune system. MHC class I proteins allow for the recognition of molecules produced within the cell, such as viral or tumor antigens, by cytotoxic T cells or killer T cells.

Let’s read about the characteristics and functions of the MHC Class I proteins:

Structure and Composition of MHC Class 1 Proteins

The MHC Class I proteins are complex transmembrane glycoproteins composed of two main components: a heavy chain, also known as the α chain, and a smaller non-covalently associated protein called β2-microglobulin.

α chain + β2-microglobulin

  • The α chain is highly polymorphic, meaning it exists in various allelic forms leading to a diverse array of MHC Class I molecules in the population.
  • The α chain consists of three domains: α1, α2, and α3. The α1 and α2 domains form a peptide-binding cleft, while the α3 domain anchors the complex to the cell membrane.
  • The β2-microglobulin which is the non-polymorphic is essential for the proper folding and stability of the MHC Class I molecule.

MHC Class II Proteins

The MHC Class II proteins are essential components of the immune system involved in antigen presentation and immune regulation. They play a crucial role in recognizing and presenting antigens derived from the extracellular pathogens to CD4+ T cells, also known as helper T cells. Let’s explore the characteristics and functions of the MHC Class II proteins.

Structure and Composition

The MHC Class II proteins consist of two transmembrane chains: an α chain and a β chain. Both chains are synthesized in the endoplasmic reticulum and form a heterodimeric complex.

The α and β chains each have two domains: α1, α2, β1, and β2. The α1 and β1 domains are responsible for the binding and presenting the antigenic peptides, while the α2 and β2 domains contribute to the overall stability and structure of MHC Class II molecule.

α chain + β chain

  • MHC class II proteins are found primarily on antigen-presenting cells like macrophages, dendritic cells, and B cells.

Difference Between MHC Class I and MHC Class II Proteins

Characteristics MHC Class I Proteins MHC Class II Proteins
Structure

The α chain + β2-microglobulin

the α chain + β chain

Cell Surface Expression

The ubiquitous (expressed on most nucleated cells)

The restricted to the antigen-presenting cells (dendritic cells, macrophages, B cells)

Antigen Source

Intracellular pathogens (viruses, intracellular bacteria)

Extracellular pathogens (bacteria, parasites)

Antigen Processing

Endogenous pathway: antigens derived from inside the cell are processed and presented on MHC Class I molecules

Exogenous pathway: antigens internalized from the extracellular environment are processed and presented on MHC Class II molecules

Peptide Size

Small peptides (8-10 amino acids)

Larger peptides (13-25 amino acids)

T Cell Interaction

The CD8+ T cells (cytotoxic T cells)

The CD4+ T cells (helper T cells)

Co-receptor

The CD8 molecule

The CD4 molecule

Immune Function

Cytotoxicity (killing infected or abnormal cells)

The immune regulation, coordination, and activation of other immune cells

Location

Present of all nucleated cells

Present primarily on antigen-presenting cells

 MHC I vs MHC II Diagram

The diagram of Major Histocompatibility Complex (MHC) Proteins are given below:

MHC I and MHC II

Conclusion – Difference Between MHC Class 1 and MHC Class 2 Proteins

In conclusion, MHC Class I proteins are expressed on most nucleated cells and present antigens from intracellular pathogens to cytotoxic T cells for cell killing. On the other hand, MHC Class II proteins are restricted to antigen-presenting cells and present antigens from extracellular pathogens to helper T cells for immune regulation and activation. Studying the difference between MHC Class 1 and MHC Class 2 Proteins helps in the understanding how the immune system distinguishes between different types of pathogens. It also aids in understanding the roles of different immune cells and their interactions in the immune response against infections.

Also Read:

FAQs on Difference Between MHC Class 1 and MHC Class 2 Proteins

What is the Role of MHC Proteins in the Immune System?

The MHC proteins play a vital role in the immune system by presenting antigens to the immune cells, which triggers an immune response against foreign substances.

Can MHC Class I and MHC Class II Proteins Present the Same Antigen?

No, MHC Class I and MHC Class II proteins present antigens derived from different sources and interact with different types of T cells.

Are MHC Class I and MHC Class II Genes Polymorphic?

Yes, MHC genes are highly polymorphic, meaning they exist in different variants or alleles within a population, contributing to the diversity of antigen presentation.

What Happens if There is a Mismatch Between MHC Proteins During Organ Transplantation?

The Mismatched MHC proteins can lead to the immune response, as the recipient’s immune system may recognize the transplanted organ as foreign and mount an immune attack, resulting in organ rejection.

What is the function of MHC Class 2?

MHC Class II proteins aid in presenting antigens derived from extracellular pathogens to CD4+ T cells, facilitating immune responses

What is the structure of MHC-I?

MHC-I has an α chain associated with β2-microglobulin, forming a heterodimeric structure crucial for antigen presentation to CD8+ T cells.



Last Updated : 27 Mar, 2024
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