Refined localization of H7 and Ctt1 on distal mouse chromosome 9

Biochemical and Immunogenetic Analysis of an Immunodominant Peptide (B6dom1) Encoded by the Classical H7 Minor Histocompatibility Locus

Of the many minor histocompatibility (H) Ags that have been detected in mice, the ability to induce graft vs host disease (GVHD) after bone marrow transplantation is restricted to a limited number of immunodominant Ags. One such murine Ag, B6dom1, is presented by the H2-Db MHC class I molecule. We present biochemical evidence that the natural B6dom1 peptide is indistinguishable from AAPDNRETF, and we show that this peptide can be isolated from a wide array of tissues, with highest levels from the lymphoid organs and lung. Moreover, we employ a novel, somatic cell selection technique involving CTL-mediated immunoselection coupled with classical genetics, to show that B6dom1 is encoded by the H7 minor H locus originally discovered ∼40 years ago. These studies provide a molecular genetic framework for understanding B6dom1, and exemplify the fact that mouse minor H loci that encode immunodominant CTL epitopes can correspond to classical H loci originally identified by their ability to confer strong resistance to tumor transplantation. Additionally, these studies demonstrate the utility of somatic cell selection approaches toward resolving H Ag immunogenetics.

Immunodominant minor histocompatibility antigen peptides presented by H2Db molecules

BACKGROUND

C57BL/6 (B6) mice generate cytolytic T lymphocytes (CTLs) to a limited number of immunodominant cytotoxic T cell target (CTT) antigens and associated peptides when primed with H2-matched BALB.B spleen cells, despite multiple minor histocompatibility antigen (HA) differences. We previously showed that these CTLs recognize four Kb-bound minor HA peptides derived from CTT antigens. Here, we describe the identification of Db-bound minor HA peptides recognized by B6 anti-BALB.B CTLs.

METHODS

Peptides were extracted from Db molecules immunoprecipitated from lysates of T lymphoblasts from BALB.B mice and mice from the CXB recombinant inbred strains that express H2b and segregate minor HA from BALB/c and B6. Peptides were separated by reverse-phase high-performance liquid chromatography and tested for sensitization of targets for lysis by CTLs specific for BALB.B and the CXB strains.

RESULTS

B6 anti-BALB.B CTLs recognized a single Db-bound peptide whose distribution in CXB strains matched that of the previously reported CTT-1 minor HA. An additional Db-bound peptide (CTT-7) was recognized by B6 anti-CXBG CTLs. CTT-1 was expressed by independently derived inbred mouse strains that express H2b. CTT-1 was recognized by B6 CTLs specific for these inbred strains, except for the LP and 129 strains that stimulated CTL specific for the CTT-8 peptide expressed by these two strains.

CONCLUSIONS

These results demonstrate that B6 CTLs primed and boosted with multiple minor HA recognize a maximum of two minor HA peptides regardless of the strain of origin of H2b-matched stimulating lymphoid cells.