Structural and immunological similarities between HLA antigens from three loci

Area of Science:

• Immunogenetics
• Molecular Biology
• Human Genetics

Background:

• Human Leukocyte Antigen (HLA) antigens are crucial for immune response.
• Existing knowledge indicates structural similarity between gene products of the first and second HLA loci.

Purpose of the Study:

• To investigate the chemical and immunological relationship of third locus HLA antigens to those of the first and second loci.
• To determine if HLA antigens across the three loci share common evolutionary origins.

Main Methods:

• Analysis of polypeptide chain composition, including identification of beta2-microglobulin in third locus antigens.
• Molecular weight determination using detergent solubilization and proteolysis.
• Gel chromatography and sedimentation velocity for size and shape analysis.
• Cyanogen bromide fragmentation and cross-reactivity studies using antibodies.

Main Results:

• Third locus HLA antigens comprise two polypeptide chains, one identical to beta2-microglobulin.
• Apparent molecular weights of the alloantigenic chain were determined under different conditions.
• Techniques employed showed indistinguishable HLA antigens from the three subloci.
• Third locus antigens exhibited greater sensitivity to proteolysis compared to first and second locus antigens.
• Polypeptide chain fragmentation and antibody cross-reactivity further supported structural similarities.

Conclusions:

• HLA antigens from the three subloci are structurally indistinguishable using the employed techniques.
• Evidence strongly supports the hypothesis that the three HLA antigen subloci originated from gene duplications of a common ancestral gene.