Abstract: Objective To investigate the role of natural anti-keratin autoantibody(AK auto Ab) in defense against Staphylococcus aureus(S.aureus)infection in vivo using AK auto Ab transgenic(Tg) mouse model.Methods Peritoneal cavity lavage fluid from Tg mice and littermate controls was analyzed by ELISA for the level of total IgM,anti-keratin IgM,and anti-S,aureus IgM.At 48 h after intraperitoneal (ip)inoculation with S.aureus,colony forming assay was used to detect the bacterial burden in abdominal cavity and kidney of these mice,and flow cytometry to assess the neutrophil percentage and inflammatory factor level in the peritoneal cavity lavage fluid of these mice.Results The IgM levels of anti-keratin and anti-S,aureus were significantly higher in Tg mice than those in the littermate controls(both P<0.01).Colony forming assay revealed that littermate controls displayed a significantly higher bacteria burden than Tg mice did(P<0.01).Both the neutrophil percentage and inflammatory factor concentration were significantly lower in Tg mice than those in the control(both P<0.01)as indicated by flow cytometry.Conclusion These findings suggest that natural anti-keratin lgM may have an excellent protective effect against S.aureus in mice.

Key words: Autoantibodies, Keratin, Staphylococcus aureus, Animal testing alternatives, Bacterial infections