Inhibition of TNF-alpha-induced sickle RBC retention in retina by a VLA-4 antagonist.
OBJECTIVE
Patients with sickle cell disease have elevated circulating levels of cytokines including tumor necrosis factor (TNF) alpha. TNF-alpha stimulates expression by endothelial cells of adhesion molecules, including vascular cell adhesion molecule (VCAM) 1. Others have demonstrated that VLA-4 (alpha(4)beta(1)), a ligand for VCAM-1 or fibronectin, is present on a fraction of sickle reticulocytes. The intent of this study was to determine, using a rat model, if TNF-alpha increases retention of sickle erythrocytes in retina and if that retention can be inhibited.


METHODS
TNF-alpha was given intraperitoneally to rats 5 hours before IV administration of FITC-labeled, density-separated sickle erythrocytes. After 5 minutes, rats were exsanguinated, and retinas were excised and incubated for ADPase activity, permitting the determination of the number and location of retained cells.


RESULTS
TNF-alpha caused a three- to fourfold increase in retention of sickle erythrocytes in retinal capillaries (P < 0.05) but not of normal human erythrocytes. Preincubation of sickle erythrocytes with TBC772, a peptide that blocks the binding of alpha(4)beta(1) and alpha(4)beta(7), or a monoclonal antibody against VLA-4 (19H8), significantly inhibited the TNF-alpha-induced retention (P < or = 0.02), whereas a control cyclic peptide and antibody had no effect. IV TBC772 also inhibited sickle erythrocyte retention (P = 0.01). Two intravenously administered anti-fibronectin antibodies inhibited sickle cell retention as well, but an anti-rat VCAM-1 antibody did not inhibit retention.


CONCLUSIONS
The authors conclude that TNF-alpha stimulates retention of sickle erythrocytes in the retinal vasculature. This increased retention can be blocked by a VLA-4 antagonist, suggesting that the cells retained after cytokine stimulation are reticulocytes. The counter-receptor for VLA-4 in this rat retina model appears to be fibronectin and not VCAM-1, based on data obtained using antibodies against these molecules.
Lutty
G A
GA
Wilmer Ophthalmological Institute, Johns Hopkins Hospital, 170 Woods Research Building, 600 N. Wolfe Street, Baltimore, MD 21287-9115, USA. glutty@jhmi.edu
Taomoto
M
M
Cao
J
J
McLeod
D S
DS
Vanderslice
P
P
McIntyre
B W
BW
Fabry
M E
ME
Nagel
R L
RL
D000755:Anemia, Sickle Cell / Q000097:blood*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D002448:Cell Adhesion / Q000187:drug effects; D004730:Endothelium, Vascular / Q000187:drug effects; D004913:Erythrocytes, Abnormal / Q000378:metabolism*; D006801:Humans; D007274:Injections, Intraperitoneal; D039041:Integrin alpha4beta1; D016023:Integrins / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000378:metabolism; D008297:Male; D008856:Microscopy, Fluorescence; D010456:Peptides, Cyclic / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D016201:Receptors, Lymphocyte Homing / Q000037:antagonists & inhibitors* / Q000276:immunology / Q000378:metabolism; D012156:Reticulocytes / Q000187:drug effects; D012171:Retinal Vessels / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D000911:Antibodies, Monoclonal; D039041:Integrin alpha4beta1; D016023:Integrins; D010456:Peptides, Cyclic; D016201:Receptors, Lymphocyte Homing; D014409:Tumor Necrosis Factor-alpha; D019010:Vascular Cell Adhesion Molecule-1