Bacterial lipooligosaccharide (LOS) antigens from Moraxella catarrhalis and nontypeable Haemophilus influenzae (LOS)

Bacterial lipooligosaccharides (LOS) are essential glycolipid components of the outer membrane of Gram-negative respiratory pathogens, specifically Moraxella catarrhalis and nontypeable Haemophilus influenzae (NTHi). Unlike the lipopolysaccharides (LPS) found in many enteric bacteria, LOS molecules lack the repeating O-antigen subunits, consisting instead of a conserved Lipid A anchor, a 2-keto-3-deoxy-octulosonic acid (Kdo) core, and a variable, branched oligosaccharide (Apicella, 2012; Murphy, 2015). These molecules serve as critical virulence factors that facilitate bacterial adherence to human respiratory epithelial cells, promote the formation of biofilms, and enable the bacteria to evade the host complement system through the recruitment of regulatory proteins like C4b-binding protein (Schultz et al., 2020). LOS also acts as a potent trigger for the innate immune system by activating the Toll-like receptor 4 (TLR4) complex, which drives the localized inflammatory response characteristic of otitis media and chronic obstructive pulmonary disease (COPD) exacerbations (Tan et al., 2005). Because of their prominent surface exposure and essential role in pathogenesis, LOS structures are primary targets for the development of conjugate vaccines and therapeutic monoclonal antibodies designed to elicit protective bactericidal immunity and prevent colonization (Yu et al., 2018). However, therapeutic development must address the inherent endotoxicity of the Lipid A component and the potential for molecular mimicry, where bacterial oligosaccharides resemble human glycosphingolipids to avoid immune detection.

Other names

LipooligosaccharideBacterial LOSEndotoxinLipid A-oligosaccharide complexM. catarrhalis LOSNTHi LOS

Induction of opsonophagocytic and bactericidal antibodies; neutralization of Lipid A-mediated TLR4 signaling; inhibition of bacterial colonization and adherence to host respiratory epithelia.