Bacteria also express surface proteins that can bind C4BP and Factor H, thereby preventing their cofactor function in Factor I-mediated cleavage of C3b/C4b and the subsequent downstream complement activation. A number of bacteria target C4BP for binding and inactivation including the M protein family members Arp and Sir, expressed by group A Streptococci and outer membrane protein OmpA expressed by Escherichia coli (for a comprehensive review, see Blom et al. 2009 ). Factor H is similarly a target for binding by proteins expressed by a number of bacteria including M protein expressed by Staphylococcus aureus and Streptococcus pyogenes and GNA1870 expressed by Neisseria meningitides ).