Eosinophils express CD49d (VLA-4) on their surface whereas neutrophils do
not. By gating on the granulocyte population (on a FS vs. SS plot), and
CD49d expression you can identify eosinophils.
The other method I've used to identify eosinophils is by polarised light
scatter. Eosinophils depolarise light to a greater extent than other white
cells so they can be distinguished quite easily. Since the laser provides
the polarized light source all you need is a polarizing filter. I've used
this method on our EPICS XL. A reference for this method is:
B.G. de Grooth, L.W.M.M. Terstappen, G.J. Puppels, and J. Greve.
Light - Scattering Polarization Measurements as a New Parameter in Flow
Cytometry. Cytometry 8:539-544 (1987).
- Maria Daly.