Characterization of human platelet binding of recombinant T cell receptor ligand.
BACKGROUND
Recombinant T cell receptor ligands (RTLs) are bio-engineered molecules that may serve as novel therapeutic agents for the treatment of neuroinflammatory conditions such as multiple sclerosis (MS). RTLs contain membrane distal α1 plus β1 domains of class II major histocompatibility complex linked covalently to specific peptides that can be used to regulate T cell responses and inhibit experimental autoimmune encephalomyelitis (EAE). The mechanisms by which RTLs impede local recruitment and retention of inflammatory cells in the CNS, however, are not completely understood.


METHODS
We have recently shown that RTLs bind strongly to B cells, macrophages, and dendritic cells, but not to T cells, in an antigenic-independent manner, raising the question whether peripheral blood cells express a distinct RTL-receptor. Our study was designed to characterize the molecular mechanisms by which RTLs bind human blood platelets, and the ability of RTL to modulate platelet function.


RESULTS
Our data demonstrate that human blood platelets support binding of RTL. Immobilized RTL initiated platelet intracellular calcium mobilization and lamellipodia formation through a pathway dependent upon Src and PI3 kinases signaling. The presence of RTL in solution reduced platelet aggregation by collagen, while treatment of whole blood with RTL prolonged occlusive thrombus formation on collagen.


CONCLUSIONS
Platelets, well-known regulators of hemostasis and thrombosis, have been implicated in playing a major role in inflammation and immunity. This study provides the first evidence that blood platelets express a functional RTL-receptor with a putative role in modulating pathways of neuroinflammation.
Department of Cell and Developmental Biology, Oregon Health & Science University, Portland, USA.
Asako
A
Itakura
Joseph E
JE
Aslan
Sushmita
S
Sinha
Tara C
TC
White-Adams
Ishan A
IA
Patel
Roberto
R
Meza-Romero
Arthur A
AA
Vandenbark
Gregory G
GG
Burrows
Halina
H
Offner
Owen Jt
OJ
McCarty
D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000378:metabolism; D003599:Cytoskeleton / Q000378:metabolism; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D006801:Humans; D008024:Ligands; D051379:Mice; D010973:Platelet Adhesiveness; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000037:antagonists & inhibitors; D011485:Protein Binding; D011948:Receptors, Antigen, T-Cell / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D013927:Thrombosis / Q000378:metabolism; D013928:Thromboxane A2 / Q000037:antagonists & inhibitors
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D008024:Ligands; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011948:Receptors, Antigen, T-Cell; D011993:Recombinant Fusion Proteins; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D004533:Egtazic Acid; D013928:Thromboxane A2; D002118:Calcium