In vivo Analysis of Neutrophil Infiltration during LPS-induced Peritonitis

Materials and Reagents

1. Insulin syringes (Thermo Fisher Scientific, catalog number: 14-841-31 )
   
2. 0.22 μm filters
   
3. C57BL/6 mice, typically of 8-12 weeks old mice (male or female)
   
4. LPS E.coli 0111:B4 (Sigma-Aldrich, catalog number: L2630-100MG )
   
5. Dulbecco's phosphate-buffered saline (DPBS) (Corning, catalog number: 21-030-CV )
   
6. XenoLight RediJect inflammation probe (PerkinElmer, catalog number: 760535 )
   
7. Luminol sodium salt (Sigma-Aldrich, catalog number: A4685 )
   
8. Isofluorane (Henry Schein, Isothesia^TM, catalog number: 10014450 )
   
9. 5 mg/ml LPS (see Recipes)
   
10. 20 mg/ml luminol sodium salt stock solution (see Recipes)
    

Equipment

1. Anesthesia machine (VetEquip, model: 901808 ) or similar anesthesia equipment
   
2. Rechargeable trimmer (Braintree Scientific, catalog number: VLP-323 75 )
   
3. Scale (Kent Scientific, catalog number: SCL66110 )
   
4. Biosafety cabinet
   
5. IVIS spectrum (PerkinElmer, model: 124262 ) or a comparable luminescence imaging equipment
   

Software

1. Living Image software (PerkinElmer)

Procedure

1. Two days before the LPS intraperitoneal injection, place mice in the anesthesia machine and once the mice are anesthetized shave abdominal area with a trimmer, as fur quenches the luminescence signal (Figure 1).
   
   
   Figure 1. A representative picture of mice under anesthesia getting their abdominal area shaved with a trimmer
   
   
2. Weigh mice.
   
3. In the day of the experiment dilute LPS in DPBS and prepare syringes for injection.
   
4. Intraperitoneally inject mice with 2.5 mg/kg of LPS or the same volume DPBS for the control group (injection volume approximately 200 μl).
   
5. 3 h later intraperitoneally inject mice with 200 mg/kg of XenoLight Rediject inflammation probe or 200 mg/kg luminol sodium salt (injection volume approximately 200 μl).
   
6. Place mice in the IMPAC6 anesthesia chamber attached to the IVIS spectrum.
   
7. Transfer mice to the IVIS spectrum and place mice abdomen facing up into the chamber and position each nose inside the cone that delivers the isofluorane (Figure 2).
   
8. Start imaging anesthetized mice 10 min post XenoLight Rediject inflammation probe injection with a 5 min exposure capturing in vivo bioluminescence generated by the activity of MPO as a marker for infiltration of neutrophils. In order to imagine 5 mice select field of view D and select 1.5 cm subject height (Figures 2 and 3) (Gross et al., 2009; Tseng and Kung, 2012).
   
   
   Figure 2. A representative example of in vivo imaging in 8 wk of age male C57BL/6 mice after i.p. injection of PBS (left) or LPS (2.5 mg/kg body weight) (right)
   
   
   Figure 3. Screen capture image of the IVIS acquisition control panel
   
   
9. Quantify the MPO signal using the Living Image software. First select region of interest (ROI) using ROI tools and choose to automatically draw measurement ROIs and perform ROI analyses to measure photon radiance. Also measure background ROI and subtract from your ROI measurement. Use average radiance to plot your graph.
   

Recipes

1. 5 mg/ml LPS
   Dilute LPS in DPBS.
   Filter sterillize with a 0.22 μm filter and aliquot stock solution at -80 °C.
   
2. 20 mg/ml luminol sodium salt stock solution
   Prepare 20 mg/ml luminol sodium salt stock solution in DPBS.
   Note: Luminol sodium salt for injection has to be prepared fresh each time in DPBS (20 mg/ml), filter sterillize with a 0.22 μm filter and protected from light until use.
   

Acknowledgments

This protocol was adapted from a previously published study (de Almeida et al., 2015). This work was supported by grants from the National Institutes of Health (AI099009 and AR064349 to C.S., AR066739 to A.D., AI120625 and AI120618 to C.S. and A.D., T32AR007611 to L.d.A., and the American Heart Association 13GRNT17110117 to C.S.).

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