Naturally processed peptides spanning the HPA-1a polymorphism are efficiently generated and displayed from platelet...

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Neonatal alloimmune thrombocytopenia (NAIT) is often caused by maternal antibodies against fetal platelet antigen HPA-1a.
• Most mothers producing anti-HPA-1a antibodies carry the human histocompatibility leukocyte antigen (HLA)-DRB3*0101 allele.
• The HPA-1a Leu(33) polymorphism is hypothesized to be part of an HLA-DRB3*0101-restricted T-helper epitope.

Purpose of the Study:

• To investigate whether peptides derived from platelet glycoprotein naturally presented by HLA-DRB3*0101 are associated with NAIT.
• To identify the specific epitopes involved in the T-helper response.

Main Methods:

• Utilized a homozygous HLA-DRB3*0101 antigen-presenting cell line.
• Pulsed cells with recombinant HPA-1a (Leu(33) plexin-semaphorin-integrin domain).
• Eluted peptides from HLA-DR molecules, fractionated using HPLC, and analyzed via tandem mass spectrometry.

Main Results:

• Identified a "nested set" of naturally presented HPA-1a-derived peptides.
• All identified peptides contained the core epitope Trp(25)-Leu(33).
• The most abundant peptide identified was the 16-mer Met(22)-Arg(37).

Conclusions:

• Naturally processed HPA-1a peptides, including the Trp(25)-Leu(33) epitope, are presented by HLA-DRB3*0101.
• These findings provide a basis for developing novel therapeutic strategies to induce tolerance in women at risk of NAIT.