Although the RBM of the SARS-CoV S protein does not involve any glycan chain, clusters of glycosylation sites are located in its vicinity (Li et al. 2005; Han et al. 2007). Large molecules such as lectins or antibodies binding to these glycans are thus expected to interfere with the S protein/ACE2 interaction. This has already been observed with mannose-specific lectins which have shown anti-viral activity against SARS-CoV by blocking virus attachment to its receptor (Keyaerts et al. 2007). Our data indicate that natural anticarbohydrate antibodies could have a similar effect. In addition to the blocking of virus attachment to its receptor, natural antibodies could block entry or opsonize viral particles leading to complement-mediated neutralization (Neil et al. 2005). Moreover, it was recently shown that natural antibodies can contribute to help the generation of cytotoxic T cells against the pathogen (Stäger et al. 2003; Dürrbach et al. 2007). These additional mechanisms of protection may also have participated to the protection of blood group O individual during the SARS outbreak.