Neutrophil labeling with [(99m)Tc]-technetium stannous colloid is complement receptor 3-mediated and increases the neutrophil priming response to lipopolysaccharide.
BACKGROUND
[(99m)Tc]-technetium stannous colloid (TcSnC)-labeled white cells are used to image inflammation. Neutrophil labeling with TcSnC is probably phagocytic, but the phagocytic receptor involved is not known. We hypothesised that complement receptor 3 (CR3) plays a key role. Phagocytic labeling could theoretically result in neutrophil activation or priming, affecting the behaviour of labeled cells. Fluorescence-activated cell sorter (FACS) analysis side scatter measurements can assess neutrophil activation and priming.


METHODS
We tested whether TcSnC neutrophil labeling is CR3-mediated by assessing if neutrophil uptake of TcSnC was inhibited by a monoclonal antibody (mAb) directed at the CD11b component of CR3. We tested if TcSnC-labeled neutrophils show altered activation or priming status, comparing FACS side scatter in labeled and unlabeled neutrophils and examining the effect of lipopolysaccharide (LPS), a known priming agent.


RESULTS
Anti-CD11b mAb reduced neutrophil uptake of TcSnC in a dose-dependent fashion. Labeled neutrophils did not show significantly increased side scatter compared to controls. LPS significantly increased side scatter in control cells and labeled neutrophils. However, the increase was significantly greater in labeled neutrophils than unlabeled cells.


CONCLUSIONS
Neutrophil labeling with TcSnC is related to the function of CR3, a receptor which plays a central role in phagocytosis. TcSnC labeling did not significantly activate or prime neutrophils. However, labeled neutrophils showed a greater priming response to LPS. This could result in labeled neutrophils demonstrating increased adhesion on activated endothelium at sites of infection.
Gallagher
Hayley
H
School of Veterinary and Biomedical Sciences, James Cook University, Townsville, Queensland 4811, Australia.
Ramsay
Stuart C
SC
Barnes
Jodie
J
Maggs
Jacqueline
J
Cassidy
Nathan
N
Ketheesan
Natkunam
N
D039481:CD11b Antigen / Q000276:immunology / Q000378:metabolism; D002478:Cells, Cultured; D003102:Colloids; D006801:Humans; D008070:Lipopolysaccharides / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism*; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D017463:Receptors, Complement 3b / Q000378:metabolism*; D017556:Technetium Compounds / Q000493:pharmacokinetics*; D017971:Tin Compounds / Q000493:pharmacokinetics*
D039481:CD11b Antigen; D003102:Colloids; D008070:Lipopolysaccharides; D019275:Radiopharmaceuticals; D017463:Receptors, Complement 3b; D017556:Technetium Compounds; D017971:Tin Compounds; C033493:technetium Tc 99m tin colloid