Cellular Barriers of the Innate Immune System
Inflammation is the observable condition that accompanies damage to the body. It is a localized response to tissue injury and to invading microorgan-isms, characterized by infiltration by granulocytes and macrophages, re-moval of dead cells and foreign cell and debris, followed by tissue repair. Inflammation confers protection by walling off an infected area from the rest of the body. This type of response in fish has been reported against bacterial, viral, fungal, protozoal and parasitic infections. In the higher ver-tebrates especially in mammals, inflammation involves mast cell degranula-tion and the release of vasoactive substances. These cause vasodilation, which increase blood flow and vascular permeability, and adhesiveness of vascular endothelial cells for phagocytic blood cells.
Some population of cells in fish display a non-induced and non-specific toxicity to foreign cells. The non-specific cytotoxic cells in fish are equiva-lent to the natural killer cells of mammals. They differ from their mamma-lian counterparts by being able to destroy a wider range of foreign cells, and they can even destroy multicellular parasites that attack fish.
In fish, macrophages, monocytes and granulocytes are phagocytic and in some species neutrophils are also phagocytic. Intracellular killing by teleost macrophages is similar but slower than found in mammals. These killing activities include lysosomal enzymes, alkaline and acid phosphatases and peroxidases. Activated macrophages produce oxygen metabolites such as super oxide anion in a process known as the respiratory burst. These oxy-gen radicals are bactericidal.