Fish Immunology (1+1)

Unit 16 - Immuno-stimulants

16.1. Introduction
During evolution the immune system has developed the mechanisms to detect foreign molecules that are part of the pathogen, so that once the pathogen enters the body of an organism these foreign molecules that are part of the pathogen are detected and activate the defense system against the pathogen. Simple presence of such foreign molecules is sufficient to trigger the immune system and can act as if pathogenic organism might have entered the body. So the administration of these foreign molecules which will act as immunostimulant can activate the defense system and keeps the defense system in alert to combat any invading pathogen.
Immunostimulant can be defines as a chemical, drug, stressor, or action that enhances the innate or non-specific immune response by interacting directly with cells of the system activating them.
Most immune-stimulants are chemical compounds which exist as structural elements of bacteria,
mycelial fungi and yeasts. However, there are also a couple of purely synthetic compounds that possess immune-stimulating properties.
The chemical nature of a number of different immune-stimulants are:

• Structural elements of bacteria (lipopolysaccarides (LPS), lipopeptides, capsular glycoproteins and muramylpeptides)
• Various ß-1,3-glucan products from bacteria (Curdlan) and mycelial fungi (Krestin, Lentinan, Schizophyllan, Scleroglucan, SSG, VitaStim)
• ß-1,3/1,6-glucans from the cell wall of baker’s yeast (MacroGard, Betafectin)
• Complex carbohydrate structures (glycans) from various biological sources including seaweed
• Peptides present in extracts of certain animals or made by enzymatic hydrolysis of fish protein
• Nucleotides, and
• Synthetic products (Bestatin, muramylpeptides, FK-156, FK-565, Levamisole).

Among all the immune-stimulants ß-1,3/1,6-glucans more effective and widely used in veterinary medicine , human medicine, and also in traditional animal farming. Because this immune-stimulants acts at a very basic level of the immune system. ie., the ß-1,3/1,6-glucan molecule is recognized by the specific receptor present on white blood cells in all animal groups, from the simple invertebrates to humans, and switches trigger the most basic defence mechanisms.