Molecular and cellular studies of human immune responsiveness to the short ragweed allergen, Amb a V

Specific immune responsiveness to the Amb a V allergen (from Ambrosia artemisiifolia, short ragweed pollen) is significantly associated with the Class II specificities, human leucocyte antigen (HLA)-DR2 and Dw2 determined by serological and MLR typing ('DR2.2'). Similarly, responsiveness to homologous Amb t V and Amb p V allergens is associated with DR2.2. We examined the deoxyribonucleic acid (DNA) sequences of HLA-DRB1, DRB5, DQB1 and DQA1 genes associated with Amb a V responsiveness using a combination of polymerase chain reaction (PCR), dot-blot and DNA sequencing methodologies. Our focus was on the highly polymorphic regions within the second-exon gene segments that are believed to encode antigen (Ag)-binding portions of the respective Class II molecules. Analysis of three patients having unusual sequence combinations of HLA-D gene sequences implicate an HLA-DR molecule (either DR αβ(I)2.2 or DRαβ(V)2.2), rather than a DQ Class II molecule, as the major Amb a V immune response (Ir) gene product. Our studies suggest that this DR2.2 molecule is usually a necessary, almost always a sufficient, requirement for high immunoglobulin E and G (IgE) and (IgG) antibody responsiveness in ragweed-allergic individuals. From an atopic DR2.2⁺ subject, we isolated three Amb a V-specific T-cell clones. Analysis revealed these clones to be DR-restricted, supporting the conclusion that the Amb a V-Ir gene is a DR and not a DQ molecule. The DRβ(I) polypeptide of DR2.2 and 2.12 was implicated in Ag presentation, since monoclonal antibody (MoAb) Hu30 (antibody specific for DRβ(I)) blocked T-cell proliferation. Amb t V and Amb p V did not stimulate these clones, but blocked Amb a V-induced response, indicating the existence of shared Amb V agretopes (Class II-binding portions of the Ags), but distinct T-cell epitopes. Our data are consistent with DRαβ(I)2.2 being the major Ir gene product controlling responsiveness to both of these Amb V homologous. These studies demonstrate the power of the allergy model for genetic and molecular studies of human immune responsiveness. Atopic allergy provides perhaps the best model for studying, in humans, the causal relationship between specific immune response and susceptibility to an immunological disease.