Lysozyme: an important defence molecule of fish innate immune system

TLDR

The fish innate immune system relies heavily on lysozyme, a ubiquitous enzyme with lytic, opsonic, and complement‑activating activity that varies with sex, age, season, temperature, pH, toxicants, infections, and stress. This review aims to synthesize current knowledge on the various lysozyme types and their expression in fish. The authors examine lysozyme distribution across tissues, fluids, and species, and discuss its functional roles in innate immunity.

Abstract

The innate immune system of fish is considered to be the first line of defence against a broad spectrum of pathogens and is more important for fish as compared with mammals. Lysozyme level or activity is an important index of innate immunity of fish and is ubiquitous in its distribution among living organisms. It is well documented that fish lysozyme possess lytic activity against both Gram-positive bacteria and Gram-negative bacteria. It is also known to be opsonic in nature and activates the complement system and phagocytes. It is present in mucus, lymphoid tissue, plasma and other body fluids of freshwater and marine fish. It is also expressed in a wide variety of tissues. Lysozyme activity has been shown to vary depending on the sex, age and size, season, water temperature, pH, toxicants, infections and degree of stressors. Here, we review our current understanding of different types of lysozyme and their expression and its role in fish innate immune system.