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MHC Class I and MHC Class II Proteins Differences in Biology Import Concepts Must to Know
Question. Difference Between MHC Class I and MHC Class II Proteins.
Answer:
Differentiating Property | MHC Class I | MHC Class II |
Definition | MHC class I are a class of major histocompatibility complex molecules found on the surface of all nucleated cells in mammals. | MHC class II are a class of major histocompatibility complex molecules mainly found on antigen presenting cells such as macrophages, dendritic cells, and B cells. |
Occurrence | MHC class I molecules are expressed on all types of nucleated cells in the body. | MHC class II molecules are expressed on the antigen presenting cells such as B cells, macrophages, and dendritic cells. |
Structure | MHC class I molecules are composed of three alpha domains and a single beta domain. | MHC class II molecules are composed of two alpha and beta domains. |
Membrane-spanning Domain | MHC class I molecules are composed of a single, membrane-spanning, alpha domain. | MHC class II molecules are composed of two membrane-spanning alpha and beta domains. |
Encoded Genes | The three main types of MHC class I genes are MHC – A, MHC – B, and MHC – C. | The main type of MHC class II gene is MHC – D. |
Encoded Chromosomes | The alpha domains are encoded on the MHC locus of chromosome and beta chains are encoded on chromosome . | MHC class II genes are encoded on the chromosome . |
Nature of Antigen Presenting | MHC class I molecules present endogenous antigens originated from the cytoplasm. | MHC class II molecules present exogenous antigens originated extracellularly from foreign bodies such as pathogens. |
Antigen-presenting Domains | The alpha and alpha domains are involved in the presentation of antigens in MHC class I molecules. | The alpha and beta domains are involved in the antigen presentation in MHC class II molecules. |
Responsive Cells | MHC class I present antigens to cytotoxic T cells. | MHC class II present antigens to helper T cells. |
Responsive Co-receptor | MHC class I molecules bind to the receptors on the cytotoxic T cells. | MHC class II molecules bind to the receptors on the helper T cells. |
Role | MCH class I is responsible for the clearance of endogenous antigens. | MHC class II is responsible for the clearance of exogenous antigens. |
Antigen | Cytosolic proteins; they sample peptides generated within the cell or those that may enter cytosol from phagosomes. | Class II molecules sample peptides outside the cell such as lysosomal proteins mostly internalized from extracellular environment. |
Enzymes involved in peptide generation | Cytosolic proteasome. | Endosomal and lysosomal proteases. |
Peptide loading of MHC | Endoplasmic reticulum. | Specialized vesicular compartment. |
Building amino acids | Possess amino acids. | Possess amino acids. |
Invariant chain | Has no invariant chain. | Has an invariant chain. |
Functional effect | Presence of abundant antigens target cell for destruction. | Presences of foreign antigens induce antibody production. |
Detection Method | Serology. | Serology and mixed lymphocyte reaction. |