Collect the peritoneal lavage, and centrifuge at 500 G onto white superfrost slides using a cytospin centrifuge. If you don't have one of these, just put a drop of cells onto the slide and let that drop dry quickly.

Then air dry the cells for 1 day, use a waterproof pen to draw around each "spot" on the slide, and stain with gill's hematoxylin.

You can identify neutrophils by their unique nuclear morphology, perform a cell count via microscopy, and get the number of neutrophils as a percentage of all cells in your peritoneal lavage.

This is a low-tech but useful protocol.

I am going to stain the peritoneal cells obtained by wash for CXCR2 and Ly6G and evaluate them by flow cytometry . The double positive cells will then be neutrophils . If you want the specific absolute number, you can use TruCount beads or similar to calculate that !

Best regards