Histophilus somni causes a variety of syndromes in cattle, including thrombotic meningoencephalitis and pneumonia, as opportunistic infection or mixed infection. However, the virulence factors of H. somni and their functional mechanisms have not been fully determined. Immunoglobulin binding protein A (IbpA), one of the surface proteins of H. somni, shares several features with virulence factors of other pathogens, and thus, is considered as a candidate of the H. somni virulence factors. We constructed the ibpA mutant strain 2336.A1 using the wild-type strain 2336 and compared the abilities of the mutant and the wild-type strain to cause cytotoxic and anti-phagocytic effects in macrophage-like cell lines and bovine primary monocytes in vitro. A remarkable cytotoxic effect associated with disruption of actin filaments was observed in bovine macrophage-like FBM-17 cells infected with strain 2336 but not with strain 2336.A1. Inhibition of phagocytosis of microspheres was found in assays with murine J774.1 macrophage cells and bovine primary monocytes infected with strain 2336 but not with strain 2336.A1. These results indicate that H. somni IbpA inhibits the phagocytic activity of macrophages and monocytes, probably by disrupting the actin filament structure. We suggest that IbpA plays an important role in the pathogenesis of H. somni via its antiphagocytic properties.
(Research Team for Bacterial/Parasitic Diseases, TEL +81-29-838-7708)
Reference:
Hoshinoo, K. et al. (2009) Microb. Pathog. 46(5):273-282.
