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Expression of a single‐chain human leukocyte antigen‐ DRA / DRB 3*01:01 molecule and differential binding of a monoclonal antibody in the presence of specifically bound human platelet antigen‐1a peptide
Author(s) -
Bouwmans Evelien E.,
Smethurst Peter A.,
Garner Stephen F.,
Ouwehand Willem H.,
Morley Sarah L.
Publication year - 2014
Publication title -
transfusion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.045
H-Index - 132
eISSN - 1537-2995
pISSN - 0041-1132
DOI - 10.1111/trf.12502
Subject(s) - epitope , monoclonal antibody , antigen , microbiology and biotechnology , human leukocyte antigen , antibody , biology , neonatal alloimmune thrombocytopenia , peptide , recombinant dna , chemistry , immunology , biochemistry , fetus , genetics , gene , pregnancy
Background Studies show that 1 in 1200 neonates have a low platelet ( PLT ) count due to alloimmunization against human PLT antigen ( HPA )‐1a (β 3 ‐ L 33). This mainly occurs in HPA ‐1a–negative mothers who are positive for the human leukocyte antigen ( HLA )‐ DRB 3*01:01 allele, but only about one‐third of cases will mount an effective alloimmune response. The development of specific treatment modalities requires that the mechanisms driving the maternal alloimmune response against the fetal PLTs be further explored. An antibody reagent that has a different binding affinity to HLA ‐ DRA / DRB 3*01:01 with and without the β 3 ‐ L 33 peptide would be a valuable reagent to study peptide presentation on maternal antigen‐presenting cells. Study Design and Methods To identify such antibodies, HLA ‐ DRA / DRB 3*01:01 was recombinantly expressed in D rosophila S 2 cells. To delineate the epitope of interesting antibodies, seven mutant HLA ‐ DRA / DRB 3*01:01 molecules were generated by site‐directed mutagenesis introducing naturally occurring amino acid changes encoded by DRB 3*02 and DRB 3*03 alleles. Results The murine monoclonal antibody ( MoAb ) DA 2 showed robust binding by enzyme‐linked immunosorbent assay to recombinant HLA ‐ DRA / DRB 3*01:01, but binding was reduced in the presence of β 3 ‐ L 33 peptide. The binding affinity of DA 2 to the mutant HLA ‐ DRA / DRB 3*0101 in which serine at P osition 60 of the β1‐chain was replaced by tyrosine was greatly enhanced. Interestingly the binding of DA 2 to the mutant was not reduced by the presence of β 3 ‐ L 33 peptide. Conclusion The results of this study generate a molecular model of the interaction of the HLA ‐ DRA / DRB 3*01:01 molecule with MoAb DA 2. This will inform functional studies with the recombinant C lass II molecules.