CD97 receptor is a defining member of the EGF-TM7 family of adhesion class receptors. To understand the biological function of CD97 in leukocyte trafficking, mAbs were applied in a variety of in vivo models, in which it was showed that application of anti-CD97 mAbs effectively blocks the accumulation of neutrophils. Results of my experiments clearly proved that anti-CD97 Abs block the accumulation of neutrophils, eosinophils but not macrophages, what could be potentially used in granulocyte-dependent disease like for example asthma. The presented data also lead to the conclusion that the numbers of circulating neutrophils are reduced after mAb treatment suggesting that they might undergo apoptosis or migrate to another location, like spleen. In the second part of my work I demonstrated that CD55KO, CD97KO and CD55-CD97KO mice display mild granulocytosis. However, the exact role of CD55-CD97 interaction in this process has not been characterized. I tried to find the mechanism responsible for granuloctyosis in these mice.