Difference Between MHC Class I and MHC Class II Proteins

MHC is an abbreviation for Major Histocompatibility Complex, which is a group of genes which code for proteins found on the surface of cells which helps the immune system to identify foreign pathogens. In humans, the MHC is also called the HLA system (Human leukocyte antigen). There are two classes of this complex – Class I and Class II. Read on to explore the differences between these two classes:

Difference Between MHC Class I and MHC Class II Proteins

MHC Class I

MHC Class II


Present on almost all cells which have a nucleus

Has a comparatively limited distribution. Typically found in dendritic cells, macrophages, and B-cells

Encoding Genes



Antigen Origin

Endogenous origins

Derived from extracellular proteins

Enzymes involved (in generating peptides)

Cytosolic Proteasome

Lysosomal and endosomal proteases

Peptide loading of MHC

Endoplasmic Reticulum

Specialized Vesicular compartment

Functional Effect

Presence of abundant antigens targets the cell for destruction

Presence of foreign antigens induce the production of antibodies

Method of Detection


Mixed lymphocyte reaction and serology

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