Acquisitive advertising conglomerate WPP has acquired a stake in Istropolitana Group, a full service advertising agency group in the Slovak Republic.Founded in 1992 and head-quartered in Bratislava, Istropolitana is a full service advertising agency comprising a number of separate businesses. The group employs 95 people and major clients include Heineken, Slovak Telecom and VUB Banka.Istropolitana's consolidated unaudited revenues for 2011 were €4.51m, with gross assets of €3.67m.The size of WPP's stake and the price it paid for it have not been disclosed.JH