Sequencing of HLA-D in responders and nonresponders to short ragweed allergen, Amb a V.

We investigated the molecular basis for the striking association between HLA-DR2,Dw2 and human immune responsiveness to the Ambrosia artemisiifolia (short ragweed) pollen allergen Amb a V by sequencing the second exons of the DRB and DQB1 genes of 17 selected ragweed-allergic Caucasoid subjects. We also studied the DQA1 allelic polymorphic regions (APRs) in these patients by dot-blotting using sequence-specific oligonucleotides (SSOs). The deduced amino acid sequences of the respective class II beta and alpha polypeptides were compared, with particular emphasis on residues in the APRs that are implicated in antigen binding. No evidence for "new" HLA-DRB or DQB sequences unique to Amb a V responders were found on sequencing seven Dw2+ subjects. This suggests that the presence of a particular Dw2-associated class II molecule usually provides a necessary, but not always sufficient condition for responsiveness to Amb a V. The HLA phenotypes of three subjects suggest that they possess novel recombinant haplotypes containing either DRB1*1501 and DRB5*0101 (DR2.2-associated) or DQB1*0602 (DQ1.2-associated) sequences. In these subjects, responsiveness to Amb a V was associated with the DR2.2 but not the DQ1.2 sequences, suggesting that DR alpha beta I or DR alpha beta V class II molecules are involved in antigen presentation. We investigated whether there may be shared HLA-D-encoded responder sequences present in all responders, including some exceptional DR2- Amb a V responders. The 13 subjects producing antibody (Ab) responses to Amb a V [either from natural exposure and/or after ragweed immunotherapy (Rx)] possessed DRB1*1501, 1601, 1602, 0103, 0402, 0404, 0801, or 1101 sequences, which share the majority of their aa residues in the APRs 2-4. Some of these shared residues might be important for the binding of a common Amb a V agretope prior to presentation of the class II Amb a V complex to the T-cell receptor (Tcr). An alternative postulate is that the recognition of two different Amb a V agretopes may be determined by the beta 1 polypeptides of molecules having the DR2 and DQw3 specificities.