The Four Pillars of the Immune System in Fish- Blood
We recently introduced the 4 pillars of the immune system in fish. This article dives into the innate and adaptive immune response system and what micronutrients are essential to support healthy immune system function.
The immune system in fish works much the same way as our immune system so take note.
Viruses enter the blood stream and attempt to infiltrate a healthy cell to replicate. The innate and adaptive immune system evolved to counter this attack using one strategy for neutralizing viruses in the bloodstream and a second for killing and removing infected cells.
Before the immune system take action it has to figure out it is under attack!
The challenge of recognizing a friend or a foe and eliminating foes falls to three different white blood cell types, NK, B and T-Cells, all members of the lymphocyte family.
Natural Killer (NK) Cells
When eggs hatch, each fish species executes its DNA- programmed development strategy. One of the early priorities is bone marrow development and inside bone marrow - NK cell production.
NK cells recognize "friends" using a system composed of chemical lock and keys. Proteins on the surface of the NK have a lock (aka antibody) that is designed to be opened by a key (aka antigen). All healthy cells that belong in the blood have the key to open the NK cell’s lock. If the NK cell bumps into something that does not have the friend key, it immediately signals the immune system that there is something wrong.
NK cells are generalists. They don't know anything specific about the invader, how it works and what defenses it has. Once a foe is detected, the immune system will immediately flood the blood stream with NK cells who have a predefined set of techniques used to kill viruses and other pathogens. This process resolves most infections but as viruses and bacteria evolve, some figure out how to avoid evade the NK cell's attack.
B-Cells & T-Cells- The Adaptive Immune System
Every virus has its own lock and key strategy. In the case of the COVID virus, the spike protein is a specific key that is designed to fit into a lock of healthy cells that are line our respiratory system.
When a fish is exposed to a pathogen for the first time, the NK cells signal the immune system that a foe has been detected.
The thymus has the task of training B-Cells how to make a new lock that fits the key that the virus is using to enter healthy cells. That process takes time, typically 3-9 days. The details of how the thymus trains B-Cells are outside the scope of this article.
Once the B-Cells figure out the lock, the immune system releases a flood of B-Cells that have the lock that fit the key that the virus uses to unlock and enter healthy cells. The B-Cells act like "fake locks" that bind with the virus (preventing that virus from infecting a healthy cell) and tagging the virus for destruction.
After remediation, the immune system keeps a few B-Cells with that lock in inventory.. effectively forming a memory bank of each virus that the animal has seen before. The next time that virus enters the bloodstream, the training process is no longer required, and thymus selects the correct B-Cell and gives instructions to make lots of copies immediately.
B-Cells and NK cells both operate in the blood.
What happens when the virus infects a cell?
This challenge is left to T-Cells. Once inside a cell, most viruses alter the surface proteins on infected cells. T-Cells are trained by the thymus to look for these antigens and build a specific lock that fits that key. In this case, the T-Cells dock with the infected cell then release acids to penetrate the cell wall membrane and neutralize whatever is inside. Like B-Cells, the Adaptive Immune System keeps an inventory of small amounts of trained T-Cells so that it can quickly copy them if a subsequent infection is detected.
How do vaccines work?
Vaccines all are designed to stimulate the adaptive immune system to build B and T-Cells prior to becoming infected by the actual virus.
The challenge with giving vaccines to fish (beyond cost) is which ones do you give? There are thousands of viruses and bacteria present in water and if you pick the right one, then you increase the odds of survival but only for the virus that the vaccine is designed for. Salmon crops have been lost to Infectious Salmon Anaemia (ISA), salmonid alphavirus (SAV), Infectious Pancreatic Necrosis(IPN) and Viral Haemorrhagic Septicaemia (VHS).
Is there a better way?
We believe that wild and farmed salmon are succumbing to viruses because their immune system is compromised by micronutrient deficiencies and poor animal husbandry esp. during the critical allometric development stage following birth.
The thymus & bone marrow are critical to both train and produce lymphocytes in large quantities and on demand. During the allometric development growth phase healthy bone marrow formation requires collagen (Vitamin C) and white blood cell production requires zinc. The thymus is degraded by mitochondrial dysfunction caused by Reactive Oxygen Species (ROS) (see Power) and ROS if left unmitigated attacks both zinc and vitamin C. Nature figured this out vectoring large amounts of astaxanthin into the yolk and early feeds rich with astaxanthin protected other micronutrients needed for rapid NK, T and B-Cell formation.
Our sister hatchery has operated over 100 RAS systems for 15 years enjoying an over 96% egg hatch to harvest yield across 200 species of warm and cold water fish. All without antibiotics or vaccines.
Dose your fish with the micronutrients their immune system needs to do its job and let nature do the rest.