MOLECULAR-IDENTIFICATION OF T-CELLS THAT RESPOND IN A PRIMARY BULK CULTURE TO A PEPTIDE DERIVED FROM A PLATELET GLYCOPROTEIN IMPLICATED IN NEONATAL ALLOIMMUNE THROMBOCYTOPENIA

Neonatal alloimmune thrombocytopenia induced by the human platelet all oantigen la (HPA1a) is characterized by generation of alloantibodies b y a mother who is homozygous for the HPA1b alloantigen and almost alwa ys HLA-DRB30101. The disease is viewed as B cell mediated but the lin kage with HLA is indicative of a role for T cells. The HPA1a and HPA1b allotypes are defined, respectively, by Leu and Pro at amino acid 33 of the beta-chain of the platelet integrin GPIIbIIIa (alpha(IIb)beta(3 )). Under the assumption that the same polymorphism may control both t he B cell epitope and constitute the MHC-bound peptide, we restimulate d PBMC from a woman with an affected child with a synthetic peptide fr om this polymorphic region. Molecular analysis of the responding T cel l repertoire identified two T cells which predominated in cultures sti mulated with the alloantigen peptide and which were absent in cultures with the autoantigen peptide. In spite of the use of different V fami lies, sequence of the CDR3 region of the T cell receptor (TCR) P-chain revealed the presence of a shared motif, L-P-SIT. Oligonucleotide pro bes specific for the CDR3 sequence indicated that these T cells were p resent in the PBMC at the highest levels immediately after delivery of the affected infant and their frequency dropped at later times.