Complexes of heparin and platelet factor 4 specifically stimulate T cells from patients with heparin-induced thrombocytopenia/thrombosis.
Heparin-induced thrombocytopenia with thrombosis (HITT) is associated with antibodies specific for complexes consisting of heparin and platelet factor 4 (PF4). Studies in individual patients with HITT have demonstrated immunoglobulin (Ig) class switching from IgM to the IgG or IgA isotypes. This transition is thought to require helper T cells, but no studies of the cellular or molecular basis of this process have yet been reported. To characterize T-cell involvement in HITT, peripheral blood mononuclear cells (PBMC) from two patients with classical HITT obtained shortly after the acute episode were restimulated with heparin:PF4 complexes, PF4 alone, heparin alone, and medium alone in the presence of autologous antigen-presenting cells (APC). Responding T cells were then examined using the technique of "spectratyping," in which sequences encoding CDR3 domains of individual V beta (BV) families are amplified and separated by gel electrophoresis. After 14 days in culture with antigen (heparin:PF4 complexes), but not after culture with PF4, heparin, or medium alone, patient cells, but not cells from normal subjects, preferentially expressed T-cell receptor (TCR)-containing beta chains of the BV 5.1 family. Nucleotide sequencing of BV 5.1 TCR CDR3 showed that each patient had a personal repertoire, but also shared a tetrapeptide motif (PGTG). These findings provide evidence that the humoral immune response associated with HITT is driven by helper T cells that presumably recognize peptides derived from PF4. Identification of a common beta-chain CDR3 motif in responding T cells from each of two patients suggests that a limited number of helper TCRs may be used to mount an antibody response to heparin:PF4 complexes. TCR spectratyping appears to offer a new way to examine the molecular basis of pathologic immune responses and may be useful in further studies of HITT and other immune-mediated hematologic disorders.
Bacsi
S
S
The Blood Research Institute, The Blood Center of Southeastern Wisconsin, Milwaukee, WI 53226-3548, USA.
De Palma
R
R
Visentin
G P
GP
Gorski
J
J
Aster
R H
RH
D000368:Aged; D000595:Amino Acid Sequence; D000925:Anticoagulants / Q000009:adverse effects / Q000494:pharmacology*; D002478:Cells, Cultured; D005260:Female; D006493:Heparin / Q000008:administration & dosage / Q000494:pharmacology*; D006801:Humans; D008213:Lymphocyte Activation / Q000187:drug effects / Q000276:immunology*; D008875:Middle Aged; D008969:Molecular Sequence Data; D010978:Platelet Factor 4 / Q000009:adverse effects / Q000494:pharmacology*; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D013921:Thrombocytopenia / Q000139:chemically induced / Q000276:immunology*; D013927:Thrombosis / Q000139:chemically induced / Q000276:immunology*
D000925:Anticoagulants; D010978:Platelet Factor 4; D006493:Heparin