Fusobacterium necrophorum leukotoxin (Lkt) (Lkt)

Fusobacterium necrophorum leukotoxin (Lkt) is a high-molecular-weight extracellular protein and the primary virulence factor of the anaerobic bacterium Fusobacterium necrophorum (Narayanan et al., 2002). It is a potent exotoxin that specifically targets and destroys host leukocytes, including neutrophils and macrophages, thereby impairing the host's primary immune defense (Tadepalli et al., 2009). In cattle, Lkt is the central driver in the development of hepatic abscesses and foot rot, leading to significant economic losses in the livestock industry (Nagaraja & Chengappa, 1998). In humans, the toxin is implicated in the pathogenesis of Lemierre's syndrome, where it facilitates the spread of infection from the oropharynx to the internal jugular vein (Riordan, 2007). The molecular mechanism involves the formation of pores in the target cell membrane, which results in osmotic lysis at high concentrations or the induction of apoptosis at lower concentrations (Narayanan et al., 2002). Because of its critical role in disease, Lkt is a major target for veterinary vaccine development, specifically in the form of toxoid-based formulations that stimulate the production of neutralizing antibodies (Nagaraja et al., 2005). While clinical management of human infections currently relies on antibiotics to eliminate the source bacteria, Lkt remains a significant target for potential adjunctive antitoxin therapies to reduce tissue damage.

Other names

Leukotoxin ALktAF. necrophorum exotoxinNecrobacillosis toxin

The leukotoxin acts by binding to the host cell membrane and forming pores, which leads to an influx of ions and water, resulting in cell swelling and osmotic lysis (necrosis) at high concentrations, or triggering apoptotic pathways at lower concentrations (Narayanan et al., 2002).