SPECIAL REPORT:
Utilizing the immune system line of defense
From the 2023 Kemin Intestinal Health Symposium
By Krissa Welshans
The immune system is key to the discussion of gut health and production. Products that stimulate the immune system or that conserve energy that would be normally used by the immune system are often discussed, but Dr. Ryan Arsenault, speaking at the 2023 Kemin Intestinal Health Symposium, said the “why” of those things aren’t necessarily discussed. He suggested that understanding some of the “whys” might engender more trust and acceptance when advocating for certain products or management systems.
“Probably the most fundamental question would be, ‘Why do we have an immune system?’” said Dr. Arsenault, associate professor of animal science at the University of Delaware. “We can talk about prevention of pathogens invading the host, whether you’re a single-cell organism or a vertebrate. You don’t want those pathogens invading your cells. They are parasites; they want to take from the host to further their own growth.”
There are two branches to the immune system in vertebrates: innate and adaptive. Arsenault said the innate system is the older system that has rapid response and recognizes patterns, while the adaptive system is slower to respond, recognizes antigens rather than patterns and has memory.
Both affect performance. The innate immune system, he explained, is like an incandescent light bulb: “It’s cheap to make but expensive to use. The light bulb itself is really inexpensive, but when you need to use it to produce light, it’s inefficient, costly.”
The adaptive immune system, on the hand, is like an LED light bulb, he explained. “It’s expensive to buy up front, but once you need to use it to produce light, it’s inexpensive.”
These differences affect production, he added.
For his presentation, Arsenault specifically focused on the adaptive system as it is “more of a mystery to some people.”
“We focus a lot on inflammation and things like that when we talk about animal production, but we don’t so much talk about the adaptive system, or the ‘acquired system,’ as it’s called.”
So, why do we have the adaptive system? Arsenault said it is newer, antigen specific and stimulates the immune system specifically. It is also more complex because it is a signal integrator; it requires multiple signals to be activated; it involves multiple organs, multiple cell types, and it has memory.
The memory aspect is key because an adaptive immune system can distinguish between pathogen subspecies. For example, Salmonella enterica has over 2,800 serovars, which are the variations within a species of bacteria or virus that the immune system can distinguish between. Research has proven distinctions can be made between Heidelberg, Kentucky, tymphumirium and enteritidus by looking at how the immune system of the bird responds to those serovars.
Further, because the adaptive immune system remembers the serovars, an animal will not get infected with a specific pathogen over and over. “It will remember and mount that response again,” said Arsenault. “Vaccination is based on this memory.”
Importance to gut microbiome
Dr. Arsenault explained that without an adaptive immune system, the gut microbiome would not be possible.
“You would not be able to have a symbiotic microbiome if we only had the innate system, because the innate system recognizes patterns and the innate system cannot tell the difference between a commensal clostridium and a pathogenic clostridium,” he said. “The adaptive system knows the difference because of its antigen specificity.”
Essentially, the adaptive immune system allows the host to receive the benefits of having a symbiotic relationship with our microbiome. “Being able to remember who’s a good guy and who’s a bad guy, who’s a commensal and who’s a pathogen allows us to foster the commensals and eliminate the pathogens,” Arsenault explained.
Ruminants, for example, wouldn’t survive without a microbiome. “They receive their energy from the fermentation that’s carried on by the microbiome of their rumen,” he said.
On the poultry side, Arsenault shared that chicken health in the U.S. is boosted because the birds are raised on dirty litter.
“We don’t clean out our barns every time, and I think that’s a good thing. If you have a healthy flock, your next flock is more likely to be healthy if you raise them on that litter. They’ve been given a chicken microbiome. That dirty litter is providing that colonization,” he explained.
Role in sustainability?
In 1950, there were 22 million dairy cows in the U.S. producing 664 gallons of milk each. In 2015, the U.S. had 9 million dairy cows producing 2,700 gallons of milk each.
Arsenault asked the Symposium attendees, “If we talk about sustainability for a second, is it more sustainable for animal production, for input cost, for energy, for the environment to raise 22 million dairy cows or 9 million dairy cows?”
Sustainability means you need a productive animal, he said. “We can’t go back to 1950s genetics; we can’t go back to slow-growing chickens, unproductive dairy cows, late-weaned pigs. That’s not the way to feed the world, and that’s not sustainable. It will take more resources, but let’s make a robust animal that’s also productive.”
Understanding the immune system and what makes it effective at preventing or responding to disease, as well as understanding how to maintain productivity, can allow agriculture to both feed the planet and protect the environment, Arsenault said.
“If we can get our production animals to the adaptive system more quickly, it will be less costly in production. Early is important to establish a microbiome; early is important to shift from an innate to an adaptive system,” he said.
For example, weaning time for pigs and cows and the point when the chicken has used up its yolk sac are critical times for this shift and for the maturation of the microbiome, Arsenault noted.
“Are you hitting the metabolic and the immune responses? We want growth and robustness, so maybe the best product would affect both. Maybe it would enhance effective metabolic pathways and stimulate that immune response,” he suggested.
Examples of this include probiotics, prebiotics and postbiotics. Inducing animals to care with something that is commensal can be beneficial, Arsenault explained.
However, he stressed the importance of knowing what products do, what production consequences they can have and how management practices can affect performance.
“Thinking about the strategic intervention that you need in your system for your problem, or the problems you suspect or are concerned about, can lead to a better strategy,” Arsenault concluded.
Watch the full presentation from Dr. Arsenault and access all 2023 Kemin Intestinal Health Symposium content at kemin.com/symposium.
“A microbe is engulfed by an antigen-presenting cell. It’s processed, that foreign microbe’s broken up and parts of it are presented on the surface of the cell. The B cell, if it has the receptor that recognizes the antigen that’s been presented on that cell, will bind to it. The T helper cell will also have a receptor and if it recognizes that same antigen, it will bind. Together, they mature the B cell to become a plasma cell. A plasma cell is basically an antibody factory, and it just secretes immunoglobulin, secretes antibody specific for that antigen that was presented on that antigen-presenting cell. A subset of those cells will become memory cells. So, there will be a B cell that’s been locked into recognizing that antigen and it will persist in your body, often for life, to respond to a second infection of that microbe. This is why vaccination works. When you see that microbe again, [it is] very likely you won’t get sick.”When that receptor recognizes that antigen, it sends a signal inside the cell and that cell starts making antigen identical to that receptor. The T cell receptor looks slightly different, but it’s still an immunoglobin.You can have part of antigen recognized by one B cell and another part of an antigen recognized by the another B cell.
