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Molecular Imaging and Contrast Agent Database (MICAD) [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2004-2013.

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Molecular Imaging and Contrast Agent Database (MICAD) [Internet].

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Microbubbles coated with anti-P-selectin antibody RB40.34

, PhD
National Center for Biotechnology Information, NLM, NIH, Bethesda, MD
Corresponding author.

Created: ; Last Update: April 17, 2012.

Chemical name:Microbubbles coated with anti-P-selectin antibody RB40.34
Abbreviated name:MB-RB40.34, MBp
Agent category:Antibody
Target category:Antigen
Method of detection:Ultrasound
Source of signal:Microbubbles
  • Checkbox In vitro
  • Checkbox Rodents
Click on protein, nucleotide (RefSeq), and gene for more information about P-selectin.



Ultrasound is the most widely used imaging modality (1) and its role in noninvasive molecular imaging with ligand-carrying microbubbles is expanding (2). Microbubbles are spherical cavities filled by a gas encapsulated in a shell. The shells are made of phospholipids, surfactant, denatured human serum albumin, or synthetic polymer. Ligands and antibodies can be incorporated into the shell surface of microbubbles. Microbubbles are usually 2 to 8 μm in size. They provide a strongly reflective interface and resonate to ultrasound waves. They are used as ultrasound contrast agents in imaging of inflammation, angiogenesis, intravascular thrombus, and tumors (3-5). They may also potentially be used for drug and gene delivery (6).

Endothelial cells are important cells in inflammatory responses (7, 8). Bacterial lipopolysaccharide, virus, inflammation, and tissue injury increase tumor necrosis factor α (TNFα), interleukin-1 (IL-1), and secretion of other cytokines and chemokines. Leukocyte emigration from blood is dependent on rolling of leukocytes along endothelial cell surfaces and subsequent adherence to endothelial cell surfaces. Inflammatory mediators and cytokines induce chemokine secretion from endothelial cells and other vascular cells and increase their expression of cell surface adhesion molecules, such as intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), integrins, and selectins. Chemokines are chemotactic to leukocytes to sites of inflammation and tissue injury. The movement of leukocytes through endothelial junctions into the extravascular space is highly orchestrated through various interactions with different adhesion molecules on endothelial cells (9).

P-selectin is found on the cell surface of endothelial cells and platelets (8, 10). It binds to glycoprotein on the cell-surface of leukocytes. IL-1 and TNFα, released from inflammatory and ischemic stimuli, stimulate P-selectin and other adhesion molecule expression on the vascular endothelial cells leading to leukocyte adhesion to the activated endothelium. P-selectin and other selectins are involved in rolling and arresting leukocytes on the endothelium. Microbubbles targeted with antibodies against P-selectin are being developed as noninvasive agents for P-selectin expression in vascular endothelial cells of inflamed and damaged tissues (11).



For targeted microbubbles, biotinylated microbubbles were first prepared by sonication of an aqueous dispersion of decafluorobutane gas, distearoylphosphatidylcholine, polyethyleneglycol (PEG)- stearate, and distearoylphosphatidylethanolamine-PEG-biotin (11). Microbubbles were combined with streptavidin, washed, and conjugated with biotinylated monoclonal antibody (RB40.34) against P-selectin (MBp) or isotype-control monoclonal antibody (R3-34) against αv integrin (MBiso). Control lipid microbubbles (MBc) were also prepared. The microbubbles are about 3.5 ± 1.4 μm in diameter. An antibody to microbubble ratio was estimated to be 102 ± 3 x 103 by flow cytometry.

In Vitro Studies: Testing in Cells and Tissues


Takalkar et al. (12) reported that MBp (5 x 106 particles/ml) perfused through the flow chamber coated with P-selectin (109 sites/μm2) at a shear stress of 0.3 dyn/cm2 accumulated at a rate of 565 mm-2 min-1. Attachment rates increased at higher plate surface densities of P-selectin and MBp detachment was reduced. Accumulation rate first increased with shear, reached a maximum stress force at ~0.6 dyn/cm2, and then decreased. Minimal microbubble attachment was observed on a plate that lacked P-selectin or was blocked with RB40.34. Microbubble detachment was tested by stepping up shear stress at 30-s intervals. Half-maximal detachment was reached at 34 dyn/cm2. Therefore, accumulation and retention of MBp is possible under physiologic flow conditions and is strongly influenced by shear stress and surface density of the target receptor. Furthermore, Rychak et al. (13) demonstrated that deformed MBp exhibited significantly greater attachment efficiency than spherical MBp at stress forces of 0.4–1.35 dyn/cm2.

Animal Studies



Lindner et al. (11) performed ultrasound assessment of inflammation with MBp by intravital microscopy of the cremasteric venules of control (n = 5) and TNFα–stimulated wild-type mice (n = 5). Retention of MBp, MBiso, and MBc increased (P<0.05) with TNFα treatment because of increased attachment to activated leukocytes. Extensive attachment of MBp directly to the endothelium was observed in TNFα–stimulated mice, resulting in retention of MBp (16 microbubbles/measurement) >3-fold (P<0.01) greater than either MBiso (4 microbubbles/measurement) or MBc (2 microbubbles/measurement). Enhanced retention of MBp was completely abolished in TNFα–stimulated P-selectin–deficient mice. Renal ultrasound imaging of the kidneys of wild-type mice (n = 5) undergoing ischemia-reperfusion injury showed that video intensity signal was significantly higher (P<0.05) for MBp (12 ± 2 U) than either MBiso (6 ± 3 U) or MBc (5 ± 3 U). In P-selectin-deficient mice (n = 3), the signal for MBp was equivalent to that from control microbubbles.

Rychak et al. (13) demonstrated that deformed MBp exhibited significantly greater attachment than spherical MBp in the cremasteric venules of TNFα–treated wild-type mice (P<0.05, n = 4). There was no difference in adhesion of deformed MBp and spherical MBp in the cremasteric venules of TNFα–treated P-selectin–deficient mice (n = 3); rather, the adhesion measurements were 6- and 2-fold lower, respectively.

Other Non-Primate Mammals


No publication is currently available.

Non-Human Primates


No publication is currently available.

Human Studies


No publication is currently available.

NIH Support

EB02185, HL07284, HL03810, HL64381


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