Researchers have uncovered new information about a cellular mechanism in the immune system that provides a critical step toward a better understanding of how antibodies evolve and improve in the human body.
The antibodies our immune system produces need fine-tuning to reach maximum effectiveness. When a vaccine or pathogen is first introduced into our bodies, antibodies produced against these agents help protect us — but need to be optimized, explained Matthew Macauley, an assistant professor with the University of Alberta’s Department of Chemistry.
“Slowly, our immune system improves the ability of the antibody to recognize their target, and makes them better and better.”
In a process called antibody affinity maturation, antibodies become better by evolving to bind more tightly to their target. This process occurs through mutations in a pseudo-random fashion. Then, as Macauley explained, in a highly orchestrated series of events, mutations that improve antibodies’ ability to recognize their target are selected.
The complex process of selecting the best antibody happens in the germinal centre, in a process called the germinal centre reaction. If the goal is to make vaccines even more effective and durable, scientists need to better understand this important location and the process by which they evolve, said PhD candidate Jhon Enterina, who was the first author of the study.
One standard approach immunologists have used to study the germinal centre for the past 20 to 30 years has been to look at specific carbohydrates on the surface of the white blood cells in the germinal centre as an identifying marker. Macauley, whose research as a network investigator with the pan-Canadian research network GlycoNet focuses on carbohydrates, took notice of this.
“We began asking ourselves, do these carbohydrates have a function? They’re probably not just there for us to identify; they’re likely serving an important role.”
B cells are the type of white blood cell that make antibodies. When B cells recognize a component of a vaccine or pathogen, it causes B cells to morph into more specialized germinal centre B cells. It is these specialized cells that have a unique set of carbohydrates on their surface. That’s where Macauley saw an opportunity to get to the bottom of the process.
“As the carbohydrates are changing in the germinal centre into a different type, we came up with a fairly simple way to test for their function: just stop them from changing and see what happens,” he said.
Macauley and his team created a specific model to prevent the changes from occurring. “This was accomplished at the genetic level. Normally an enzyme gets turned off in germinal centre B cells, so we simply didn’t allow the cells to turn it off.”
In doing so, they found key information about the mechanisms taking place in the germinal centre.
“We connected those changes to a protein receptor called CD22 that recognizes the key carbohydrates.”
The germinal centre is especially challenging to study because it can’t readily be studied in a petri dish. Once germinal centre cells are taken outside of their natural environment in the body, they die within a few hours. Additionally, the cells within the germinal centre divide at the fastest rate of all mammalian cells, even faster than cancer cells.
The reason these cells divide so rapidly is that it’s critical for our bodies to evolve antibodies as fast as possible to neutralize pathogens before it’s too late, said Macauley.
Many diseases, such as cancer or autoimmune diseases, stem from the germinal centre getting out of control. However, before scientists can find out how to control this key area in the body, “we need to know what proper controls are in the first place, and are still a long way from having all the answers,” noted Macauley.
“It’s a very complex process. And despite all of the insights that have been made in the last 10 years, there are still many questions about the germinal centre, so this is providing another insight into one of the mechanisms that controls it.”
The research was supported by grants from the National Institutes of Health and the Natural Sciences and Engineering Research Council of Canada, as well as a Canada Research Chair in Chemical Glycoimmunology to Macauley and a fellowship from the Canadian Arthritis Society and an Alberta Innovates graduate student scholarship to Enterina.
The study, “Coordinated changes in glycosylation regulate the germinal centre through CD22,” was published in Cell Reports.
| By Adrianna MacPherson
Adrianna is a reporter with the University of Alberta’s Folio online magazine. The University of Alberta is a Troy Media Editorial Content Provider Partner.
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