Major Histocompatibility Complex Flashcards
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Questions and Answers

What do MHC genes code for?

The expression of cell surface proteins that function, among other things, to present antigen.

Where are MHC genes found in humans?

Chromosome 6.

What is the term for MHC in humans?

HLA.

What is the term for MHC in mice?

<p>H-2.</p> Signup and view all the answers

What are MHC proteins often called?

<p>MHC antigens.</p> Signup and view all the answers

How does a recipient's immune system recognize MHC molecules in a tissue transplant?

<p>As foreign.</p> Signup and view all the answers

Where are MHC class I molecules found?

<p>On essentially all nucleated cells.</p> Signup and view all the answers

Where are MHC class I genes found?

<p>In the HLA-A, HLA-B, and HLA-C regions of the complex.</p> Signup and view all the answers

What is the primary immunological function of MHC class I?

<p>To present antigen to CD8+ T cells (CTLs).</p> Signup and view all the answers

Where are MHC class II molecules normally found?

<p>On antigen-presenting cells (B cells, macrophages, dendritic cells).</p> Signup and view all the answers

What is the primary immunological function of MHC class II?

<p>Presents antigen to CD4+ T helper cells.</p> Signup and view all the answers

What do MHC class III genes code for?

<p>Complement components and tumor necrosis factor (TNF).</p> Signup and view all the answers

Which MHC class I genes code for an alpha chain?

<p>The HLA A, B, and C genes.</p> Signup and view all the answers

In MHC class I, where are the 3 globular domains located?

<p>External to the cell membrane.</p> Signup and view all the answers

What is B2 microglobulin?

<p>A small globular peptide non-covalently linked to the a3 domain of the a chain.</p> Signup and view all the answers

Where does B2 microglobulin come from?

<p>Chromosome 15.</p> Signup and view all the answers

What do the a1 and a2 chains form in MHC class I?

<p>A binding groove for binding antigen.</p> Signup and view all the answers

What occurs in the a1 and a2 domains of MHC class I?

<p>Major structural variability.</p> Signup and view all the answers

What are MHC class II molecules composed of?

<p>An a chain with external domains a1 and a2, and a b chain with external domains b1 and b2.</p> Signup and view all the answers

In MHC class II molecules, what is between the a and b chain?

<p>Antigen-binding groove.</p> Signup and view all the answers

What prevents self-antigens from binding to MHC class II?

<p>Invariant chain that occupies the antigen-binding site.</p> Signup and view all the answers

How many distinct MHC class I molecules will any nucleated cell express?

<ol start="6"> <li></li> </ol> Signup and view all the answers

How many different MHC class II molecules will APC cells express at least?

<p>At least 6.</p> Signup and view all the answers

What is determinant selection model?

<p>It is the property of selective binding and presentation of peptides that determines which peptides will be presented.</p> Signup and view all the answers

What are endogenous antigens?

<p>Those that are synthesized by the same cell that is producing the MHC class I molecule.</p> Signup and view all the answers

What are proteosomes?

<p>Proteinase complexes in the cytoplasm that process endogenous antigens into peptides 8-11 amino acids in length.</p> Signup and view all the answers

Processed endogenous peptides are transported to the _________ where they are loaded into the ___________ of newly synthesized MHC class I molecules.

Signup and view all the answers

What do MHC genes code for?

<p>The expression of cell surface proteins that function to present antigen.</p> Signup and view all the answers

Where are MHC genes found in humans?

<p>Chromosome 6.</p> Signup and view all the answers

What is the MHC termed in humans?

<p>HLA.</p> Signup and view all the answers

What is the MHC termed in mice?

<p>H-2.</p> Signup and view all the answers

What are MHC proteins often called?

<p>MHC antigens.</p> Signup and view all the answers

How does a recipient's immune system recognize MHC molecules in a tissue transplant?

<p>As foreign.</p> Signup and view all the answers

Where are MHC class I molecules found?

<p>On essentially all nucleated cells.</p> Signup and view all the answers

Where are MHC class I genes found?

<p>In the HLA-A, HLA-B, and HLA-C regions.</p> Signup and view all the answers

What is the primary immunological function of MHC class I?

<p>To present antigen to CD8+ T cells.</p> Signup and view all the answers

What are MHC class II genes a product of?

<p>In the HLA-D region.</p> Signup and view all the answers

Where are MHC class II molecules found?

<p>On antigen-presenting cells.</p> Signup and view all the answers

What is the primary immunological function of MHC class II?

<p>Presents antigen to CD4+ T helper cells.</p> Signup and view all the answers

What does MHC class III contain genes that code for?

<p>Complement components and tumor necrosis factor.</p> Signup and view all the answers

Which MHC class I genes code for an alpha chain?

<p>The HLA A, B, and C genes.</p> Signup and view all the answers

In MHC class I, where are the three globular domains located?

<p>External to the cell membrane.</p> Signup and view all the answers

Describe B2 microglobulin.

<p>It is a small globular peptide non-covalently linked to the a3 domain of the a chain.</p> Signup and view all the answers

B2 microglobulin is not produced by which chromosome?

<p>Chromosome 15.</p> Signup and view all the answers

In MHC class I, what do the a1 and a2 chains form?

<p>A binding groove for binding antigen.</p> Signup and view all the answers

What occurs in the a1 and a2 domains of MHC class I?

<p>Major structural variability.</p> Signup and view all the answers

MHC class II molecules are composed of which chains?

<p>A chain with external domains a1 and a2, and b chain with external domains b1 and b2.</p> Signup and view all the answers

MHC class II, both a and b chains have what?

<p>Transmembrane domain and a cytoplasmic tail.</p> Signup and view all the answers

What is between the a and b chains in MHC class II molecules?

<p>Antigen-binding groove.</p> Signup and view all the answers

What accounts for binding specificity in MHC class II molecules?

<p>Variability in the amino acid sequence of the a1 and a2 domains.</p> Signup and view all the answers

What prevents self-antigens from binding in MHC class II molecules?

<p>An invariant chain occupies the antigen-binding site.</p> Signup and view all the answers

How many distinct MHC class I molecules will any nucleated cell express?

<ol start="6"> <li></li> </ol> Signup and view all the answers

MHC class II APC cells will express at least how many different molecules?

<p>At least 12.</p> Signup and view all the answers

Expression of MHC molecules is what?

<p>Limited.</p> Signup and view all the answers

Each MHC molecule must be able to do what?

<p>Bind and present multiple peptides.</p> Signup and view all the answers

What is the determinant selection model?

<p>It describes the selective binding and presentation of peptides that determines which peptides will be presented.</p> Signup and view all the answers

What are immunodominant epitopes?

<p>Epitopes that will induce an immune response.</p> Signup and view all the answers

What types of antigens do MHC class I present?

<p>Endogenous antigens.</p> Signup and view all the answers

What are endogenous antigens?

<p>Those synthesized by the same cell producing the MHC class I molecule.</p> Signup and view all the answers

What are proteasomes?

<p>Proteinase complexes in the cytoplasm.</p> Signup and view all the answers

Processed endogenous peptides are transported to the __________.

<p>rough endoplasmic reticulum</p> Signup and view all the answers

Antigen-loaded MHC class I molecules are then transported through the __________.

<p>Golgi apparatus</p> Signup and view all the answers

MHC class I molecules that are not loaded with antigen are __________.

<p>degraded intracellularly</p> Signup and view all the answers

MHC class II molecules present antigens of what origin?

<p>Exogenous origin.</p> Signup and view all the answers

MHC class II are synthesized in the _______ and transported through the ________.

<p>RER, Golgi apparatus</p> Signup and view all the answers

MHC class II gamma chain is hydrolyzed off the __________.

<p>Ag-binding groove.</p> Signup and view all the answers

Once the antigen-loaded MHC molecule is expressed on the cell surface, what can it do?

<p>Present antigen to any cell with the appropriate receptor.</p> Signup and view all the answers

What do CD4, CD8, and TCR recognize in the immune system?

<p>Processed Ag and MHC.</p> Signup and view all the answers

The CDR 1 and 2 regions bind to what component of MHC?

<p>Alpha helices.</p> Signup and view all the answers

While MHC molecules display specificity, what do they have broader specificity than?

<p>Antibodies and TCRs.</p> Signup and view all the answers

Class I molecules bind peptides that are _ to _ amino acids long.

<p>8-11</p> Signup and view all the answers

Class II molecules bind __ to __ amino acid length peptides, although the optimal length is __ to __ amino acids.

<p>10-30, 12-16</p> Signup and view all the answers

What do MHC molecules bind?

<p>Both foreign and self peptides.</p> Signup and view all the answers

How do T cells discriminate between self and non-self?

<p>Via the specificity of the TCR.</p> Signup and view all the answers

What type of structures are T cell epitopes often?

<p>Hydrophobic or aromatic peptide fragments.</p> Signup and view all the answers

Many T cell epitopes are processed peptide fragments from where?

<p>From the interior or other areas of the intact antigen.</p> Signup and view all the answers

Study Notes

Major Histocompatibility Complex (MHC) Overview

  • MHC genes encode proteins that present antigens on cell surfaces, aiding in immune responses.
  • Human MHC is identified as HLA, while in mice it is referred to as H-2.
  • MHC genes in humans are located on chromosome 6; in mice, they reside on chromosome 17.

MHC Class I

  • MHC class I molecules are present on all nucleated cells and are essential for presenting endogenous antigens to CD8+ T cells (cytotoxic T lymphocytes).
  • Key regions for MHC class I genes include HLA-A, HLA-B, and HLA-C, which code for an alpha chain involved in the formation of a binding groove for antigens.
  • B2 microglobulin, a non-covalently linked small globular peptide, comes from chromosome 15 and is associated with MHC class I.
  • MHC class I presents peptides that are typically 8-11 amino acids in length, with structural diversity in the a helices and b pleated sheets enhancing binding specificity.

MHC Class II

  • MHC class II is primarily found on professional antigen-presenting cells (APCs), such as B cells and dendritic cells, and presents exogenous antigens to CD4+ T helper cells.
  • Composed of both an alpha (containing a1 and a2 domains) and a beta (containing b1 and b2 domains) chain, MHC class II molecules have a transmembrane domain and a cytoplasmic tail on both chains.
  • The antigen-binding groove in MHC class II is formed between the two chains, enabling the binding of larger peptides (10-30 amino acids, optimal being 12-16).
  • MHC class II molecules prevent self-antigen binding initially by associating an invariant chain that occupies the antigen-binding site during intracellular assembly.

Peptide Binding and Presentation

  • MHC molecules exhibit broad specificity, allowing them to bind both foreign and self-peptides, crucial for T cell recognition.
  • T cell receptors (TCRs) recognize the peptide-MHC complex, with CDR regions binding specifically to MHC helices and the processed antigen.
  • Determinant selection model describes the selective binding of peptides to MHCs, influencing which peptides are presented and eliciting immune responses.
  • Immunodominant epitopes are those that primarily stimulate an immune reaction, which often consist of hydrophobic or aromatic peptide fragments.

Expression and Genetic Diversity

  • Each nucleated cell expresses six distinct MHC class I molecules due to inheritance from both parents.
  • MHC class II molecules, formed from two chains with three major genes (DR, DP, DQ) for each chain, can display varying configurations, increasing possible antigen presentation.
  • MHC expression is inherently limited, ensuring that a variety of peptides can compete for binding and presentation. However, not every peptide processed within the cell is presented outside.

Importance in Immune Response

  • MHC molecules play a critical role in the immune system, enabling T cells to differentiate between self and non-self entities through their unique TCR specificity.
  • Antigen-loaded MHC molecules that reach the cell surface can present antigens to any T cell with appropriate receptors, which is vital for mounting an effective immune response.
  • Class I molecules are crucial for recognizing and responding to endogenous threats, typically viral, while class II molecules are key for recognizing exogenous antigens encountered by APCs.

Key Mechanisms and Processes

  • Proteasomes degrade intracellular proteins into peptide fragments that are 8-11 amino acids long, suitable for MHC class I.
  • Processed peptides are transported to the rough endoplasmic reticulum to be loaded into MHC class I antigen-binding grooves before being expressed on the cell surface.
  • MHC class II molecules, synthesized in the endoplasmic reticulum, fuse within vesicles containing processed antigens from phagocytosis, facilitating external presentation.

Overall, the MHC is vital in shaping the adaptive immune response by presenting diverse peptide antigens, ensuring recognition and response to infections while maintaining self-tolerance.

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Test your knowledge on the Major Histocompatibility Complex (MHC) with these flashcards. Learn about the genes, their functions, and differences between humans and mice. Perfect for students studying immunology or genetics.

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