Identification of Leukotoxin and other vaccine candidate proteins in a Mannheimia haemolytica commercial antigen

Tucci, Paula; Estevez, Verónica; Becco, Lorena; Cabrera-Cabrera, Florencia; Grotiuz, Germán; Reolon, Eduardo; Marín, Mónica

LKT is a potent cytolytic toxin, with an apparent molecular weight (MW) of 105 kDa, actively secreted by all serotypes of the bacterium during the logarithmic phase of in vitro growth (Shewen and Wilkie, 1985; Chang et al., 1987) . It belongs to the family of the RTX (repeat in toxin) pore-forming cytolysins, which have been linked with the virulence of other bacterial species (Lo et al., 1987; Lainson et al., 1996) . It specifically targets ruminant leukocytes and plays a major role in pathogenesis of BRD by impairing the primary lung defense mechanism and by inducing inflammation as a consequence of leukocyte lysis (Conlon et al., 1991) . This phenomenon has been correlated with its ability to bind and interact with the ruminant beta2-integrin Lymphocyte Function-associated Antigen 1 (LFA-1) (CD11a/CD18) (Zecchinon et al., 2005; Singh et al., 2011) . Neutralizing antibodies generation against the cytolytic toxin is relevant for achieving a high level of protection (Mosier et al., 1989) . Immunity against M. haemolytica also requires antibodies against bacterial cell surface antigens (Shewen and Wilkie, 1988) and iron-regulated outer membrane proteins (Potter et al., 1999) .