Lectins of the innate immune system and their relevance to fish health

Innate immunity is a key component of disease resistance in vertebrates. Instead of relying on antibodies for pathogen recognition, innate immunity consists largely of pattern-based recognition of non-self cells, often through the arrangement of carbohydrates on their surfaces. In mammals, the proteins that recognize these carbohydrates are soluble lectins known to play key roles in the innate immune system and to affect overall disease resistance. These lectins would be expected to play an equal or greater role in fish, in which acquired (i.e. antibody-mediated) immunity is more variable. There are many reports of lectin or agglutinin activities in fish. However, there are few in which the protein has been biochemically characterized or analysed with respect to pathogen recognition or immunity in the host animal. Several laboratories have recently begun to work towards the identification and the structural and functional characterization of fish lectins. Development in this area may provide new tools for prevention, monitoring, and treatment of disease in fish.