Major Histocompatibility Complex (MHC) Molecules Quiz

Significance of Polymorphic Genes of MHC Molecules

• Polymorphic genes enhance the diversity of MHC molecules, allowing for a broad range of antigen presentation.
• Increased diversity improves the immune system's ability to recognize and respond to various pathogens.

Target Cell Types for CD8+ CTLs

• CD8+ cytotoxic T lymphocytes (CTLs) target cells that express MHC class I molecules, typically found on all nucleated cells.
• This interaction is crucial for the elimination of virus-infected or malignant cells.

Co-Dominant Expression of MHC Genes

• Co-dominant expression ensures that both inherited alleles from parents are expressed, increasing the variety of MHC molecules on the surface of cells.
• This maximizes the potential for antigen presentation to T cells, enhancing immune response effectiveness.

Cell Types Interacting with CD4+ Helper T Lymphocytes

• CD4+ helper T lymphocytes interact primarily with cells presenting MHC class II molecules, commonly found on antigen-presenting cells (APCs) such as dendritic cells, macrophages, and B cells.
• This interaction is critical for activating the adaptive immune response.

Significance of Codominant Expression of HLA Proteins

• Codominant expression of human leukocyte antigen (HLA) proteins allows for the presentation of a more diverse array of peptides to T cells, improving immune vigilance and responses to infections.

Cells Expressing Class II Molecules

• Class II MHC molecules are mainly expressed on professional antigen-presenting cells, including dendritic cells, macrophages, and B cells.
• These cells play a pivotal role in initiating and regulating immune responses.

Cytokine Inducing Class II Molecule Expression

• Interferon-gamma (IFN-γ) is a cytokine that can induce the expression of MHC class II molecules on non-classical APCs, broadening their ability to present antigens.

Number of Polymorphic Class I Genes in Humans

• Humans possess multiple polymorphic class I genes, specifically HLA-A, HLA-B, and HLA-C, each contributing to the diversity of MHC class I molecules.

Terminology for MHC Gene Set

• The set of MHC genes present on each chromosome is referred to as the Major Histocompatibility Complex (MHC) haplotype, representing a collection of genes inherited together.

Sibling Testing for Transplantation

• Siblings are often tested for compatibility as organ donors before unrelated individuals due to the higher probability of genetic matching and reduction of transplant rejection risks.

Modern Designation of Individual Alleles

• Individual alleles of MHC genes are designated according to a numerical system that includes the gene name followed by an asterisk and the specific allele number (e.g., HLA-DRB1*01).

Peptide-Binding Cleft Function

• The peptide-binding clefts of MHC molecules bind to specific peptides derived from protein antigens, facilitating T cell recognition.

Peptide Presentation Capacity

• Each MHC molecule can present a single peptide at a time to T cells, a crucial step for the activation of an adaptive immune response.

Essential Component for Antigen Display Function

• Proper folding and stable binding of peptides in the MHC molecule's cleft are essential for its antigen display function.

Recognition of Protein Antigens by T Cells

• MHC-restricted CD4+ and CD8+ T cells recognize protein antigens due to the specific presentation of peptide fragments in the context of MHC molecules, linking innate and adaptive immunity.

Test your knowledge on the properties and significance of MHC molecules and genes, including their role in immune responses and interaction with CTLs. Explore the polymorphic genes and their impact on presenting and responding to microbial peptides.