Galectins are beta-galactoside animal lectins which possess similar carbohydrate recognition domains and have important roles in the development and regulation of innate and adaptive immunity. Galectins have been previously shown to modulate inflammatory responses to bacterial infections, however nothing is known about the functions of different galectins during meningococcal disease.
Here I describe the interaction between galectins, in particular galectin-3, and Neisseria meningitidis, a commensal of the human respiratory tract that occasionally causes septicaemia and meningitis. Immunohistochemical analyses showed that expression of galectin-3, but not galectin-1 and galectin-8, is increased in tissues of mice following challenge with N. meningitidis; furthermore, galectin-3 staining co-localises with the bacterium in tissues from patients with meningococcal disease.
The molecular basis of interaction between N. meningitidis and exogenous galectin-3 was investigated by identifying both the bacterial structures and the regions of galectin-3 involved. Binding of galectin-3 to N. meningitidis was shown to be dependent on bacterial lipopolysaccharide (LPS), while inhibition assays with lactose and the use of truncated versions of galectin-3 demonstrated that the C-terminal carbohydrate recognition domain is necessary, but not sufficient, for the interaction. Furthermore, the biological consequences of interaction of bacteria with galectin-3 were investigated. Exogenous galectin-3 did not affect adhesion of N. meningitidis to epithelial cells, but increased the attachment of bacteria to phagocytic cells; silencing of galectin-3 expression in phagocytes did not alter the interaction of N. meningitidis with cells.
In summary, galectin-3 binds to N. meningitidis via LPS and affects meningococcal interaction with phagocytic cells. The potential role of galectin-3 in pathogen recognition is discussed.