Professor Oppermann's research interests initially focused on immunoregulatory functions of the complement system, an important humoral element of innate immunity which consists of more than 20 soluble and membrane-bound proteins. Since 1996 his main research focus has been on chemokine receptors (CCR5, CXCR4) and their signalling mechanisms. These receptors are members of the GPCR superfamily, the largest known family of membrane proteins and certainly among the oldest devices devoted to cellular signalling. Chemokine receptors fulfil important roles in the homing and directed trafficking of immune cells to sites of inflammation. Importantly, these receptors also form entry ports for several pathogens, such as HIV-1/-2 (CCR5, CXCR4).