Response to Letter to the Editor, “The Role of Membrane Attack Complex Formation against Gram-positive Bacteria”

Abstract

It has long been accepted that Gram-positive bacteria resist the membrane attack complex (MAC) because of a protective, thick peptidoglycan layer (Joiner et al. 1983). However, this is contradicted by reports showing that MAC components are assembled on Gram-positive bacteria in specific localizations and that this assembly differs among bacterial strains (Berends et al. 2013). Also, MAC components’ deficiency increases patients’ susceptibility to infections not only with Gram-negative but also with some Gram-positive bacteria (Skattum et al. 2011). Moreover, many Gram-positive bacteria not only recruit the host inhibitors of MAC but also express proteins that inhibit MAC formation (Laursen et al. 2010). For example, Streptococcus pyogenes secretes streptococcal inhibitor of complement, which blocks the C5b-7 membrane insertion site and thereby prevents MAC formation (Akesson et al. 1996). This shows clearly that the peptidoglycan wall is not enough to protect all Gram-positive bacteria from MAC lysis.