LACK OF BINDING OF PEPTIDES CARRYING THE HUMAN PLATELET ANTIGEN-1 (HPA-1) DIMORPHISM TO PURIFIED HLA-DRW52A MOLECULES

The strong association between anti-HPA-1a alloimmunization and DR3, DRw52a phenotype in HPA-1b homozygous women suggests that these class II molecules play a crucial role in the immune response against HPA-1a. The diallelic system HPA-1 results in a single amino acid polymorphism at the residue 33 of the glycoprotein IIIa, So, we tested the binding of peptides from the 25-42 region of the GPIIIa to purified HLA-DR3 and -DRw52a molecules, using a solid phase assay and a liquid phase peptide binding assay. No binding was demonstrated, indicating that either the crucial region for binding to class II molecules is not the 25-42 region, or that other events only occurring << in vivo >> are required for binding. These results may also suggest an indirect role of the residue 33 for T-cell stimulation.