The present invention relates to the use of Yersinia outer protein M (YopM), a YopM fragment, or a YopM variant, which is capable of autopenetrating the cell membrane and of integrating into the cell cytosol without the requirement of additional factors for delivering a cargo molecule across the membrane to the cytosol of a cell. The present invention also relates to a pharmaceutical composition comprising YopM, a YopM fragment, or a YopM variant being capable of autopenetrating the cell membrane and of integrating into the cell cytosol without the requirement of additional factors for the regulation of inflammatory reactions of the immune system and the treatment of diseases caused by autoimmunity of the host. The present invention further relates to a YopM fragment or variant, which is capable of autopenetrating the cell membrane and of integrating into the cell cytosol without the requirements of additional factors as well as such proteins or YopM linked to a cargo molecule.