**1. Introduction**

Peripheral occlusive diseases, including atherosclerosis, myocardial infarction and stroke, are a wide spectrum of arterial-based pathologies, reported as one of the leading causes of death worldwide [1]. Currently, the therapeutic options mainly consist of surgical interventions such as

balloon dilatation and stent implantation, as well as bypass surgery [2]. However, the body possesses an endogenous mechanism to compensate for stenosis and obstructions by forming natural bypasses. This process is called arteriogenesis [3]. Understanding the mechanisms of arteriogenesis can help to design new therapeutic options to accelerate the process of arteriogenesis in patients with the final aim of minimizing invasive interventions and avoiding amputation.

Previous studies, predominantly performed on murine hindlimb models [4], showed that arteriogenesis essentially depends on the recruitment of leukocytes to the perivascular space, where these cells subsequently supply growth factors for collateral remodeling [5,6]. At present, immunohistochemical (IHC) staining is the technique of choice for analyzing and quantifying the leukocyte subpopulations involved in this process. However, this method is very time-consuming. Analysis by flow cytometry offers an elegant and time-saving alternative to IHC especially in regard to the quantification of leukocytes.
