Ir gene function in an I-A subregion mutant B6.C-H-2bm12

Area of Science:

• Immunogenetics
• Transplantation immunology
• T cell biology

Background:

• The B6.C-H2bm12 (bm12) mouse strain possesses a mutation within the I-A subregion of the H-2 complex.
• This mutation results in the loss of detectable Ia antigens and elicits strong graft rejection and mixed lymphocyte responses between parent and mutant strains.
• It was hypothesized that the mutation affected the Ia-1 gene, prompting an investigation into the relationship between Ia antigens and immune response (Ir) genes.

Purpose of the Study:

• To determine the precise relationship between Ia antigens and Ir genes.
• To investigate the role of the Ia-1 gene in immune responses.
• To analyze the impact of the bm12 mutation on T cell-mediated immunity.

Main Methods:

• Comparative analysis of immune responses between the parent (C57BL/6) and mutant (bm12) mouse strains.
• Assessment of immune responses to synthetic polypeptide antigens: poly(L-Tyr,LGlu)-poly(DLAla)--poly(LLys), poly(Phe,Glu)-poly(DLAla)--poly(LLys), and poly(His,Glu)-poly(DLAla)--poly(LLys).
• Evaluation of cytotoxic T lymphocyte generation against the male-specific H-Y antigen in both strains.

Main Results:

• Immune responses to the tested synthetic polypeptide antigens were identical in both parent and mutant strains, indicating Ia-1 and the Ir genes for these antigens are distinct.
• The bm12 mutant strain failed to generate cytotoxic T lymphocytes against the H-Y antigen, a response typically controlled by I-A subregion Ir genes.
• Complementary Ir genes within the H-2b haplotype for H-Y antigen response were identified using the bm12 mutant.

Conclusions:

• The Ia-1 gene, located in the I-A subregion, is crucial for the immune response to the male-specific H-Y antigen.
• The mutation in the bm12 strain specifically disrupts H-Y antigen recognition, not general immune responsiveness to other antigens.
• This study establishes the Ia-1 gene as the Ir gene controlling H-Y antigen-specific cytotoxic T lymphocyte responses.