Biochemical evidence that equine leucocyte antigens W13, W22 and W23 are present on horse major histocompatibility complex class II molecules.

The research paper discusses the identification of equine leukocyte antigens W13, W22 and W23 on horse major histocompatibility complex (MHC) class II molecules through biochemical tests that involved immunoprecipitation and molecular weight determination.

Understanding MHC Class I and Class II Antigens

• The study alludes to two main types of major histocompatibility complex (MHC) molecules, namely, class I and class II.
• Typically, MHC refers to proteins found on the surface of cells that help the immune system distinguish between self and non-self entities.
• MHC class I molecules are chiefly found on all nucleated cells and are responsible for presenting endogenous antigens to the immune system, primarily to alert the body against intracellular pathogens like viruses.
• MHC class II molecules, on the other hand, primarily exist on immune cells, such as B cells, macrophages, and dendritic cells. These molecules present exogenous antigens, effectively alerting the immune system against extracellular pathogens like bacteria.

Characterizing Horse Alloantisera

• The research team biochemically characterized a number of horse alloantisera, which are antibodies produced in response to an antigen from members of the same species, as against MHC class I or class II antigens.
• The characterization process involved immunoprecipitation, which is a method used to purify antibodies from complex mixtures such as horse alloantisera using monoclonal or polyclonal antibodies.
• The antigens were immunoprecipitated from radiolabeled lymphocyte lysates, a method where cells are broken open to release their contents for further analysis.

Determination of Molecular Weights of Antigens

• Following immunoprecipitation, the molecular weights of these antigens were determined using a technique known as SDS-PAGE and fluorography.
• SDS-PAGE, or Sodium Dodecyl Sulphate Poly-Acrylamide Gel Electrophoresis, is a method used for separating proteins based on their molecular weights.
• Fluorography is an imaging technique used to visualize radioactive compounds, thus enabling measurement of the molecular weights of the radiolabelled antigens.
• Sera recognizing A2 and A3 specificities were found to have precipitated antigens with a molecular weight of 44,000 Daltons (class I heavy chain). In contrast, sera with specificities W13, W22, and W23 precipitated antigens corresponding to class II dimers (30,000 and 32,000 Daltons).

Comparison with Human MHC Molecules

• Finally, the research team compared the gleaned results with those derived from the use of cross-reacting antibodies directed against human MHC class I and II molecules. These tests confirmed that discoveries made about the horse MHC molecules were indeed valid.