Early life B cell programs such as affect long-term immune health

B cells and the antibodies they produce play an important role in our immune system, protecting us from the microscopic enemies that make us sick
.
Uncovering how they are formed and "programmed" during development is key to
better understanding the immune system's response to infection and vaccination.
A new study by researchers at Lund University in Sweden provides new insights into the origin and development of B cells in the body and gut, with implications
for long-term immune health.

The immune system is our body's first line
of defense against invading antigens, bacteria or viruses.
B cells are a type of lymphocyte or white blood cell that plays a key role
in our immune response to these microbial invaders.
They release antibodies, a special protein that locks on to the invader's antigens, making it easier for other immune cells to attack and destroy them
.
A special group of B cells, called memory B cells, remembers many previously defeated microbes so that when they enter the body again, the immune system can quickly recognize and destroy them
.

"We found that a large portion of adult B cells develop in the first few days of life
.
We hope that the identification of the time window in which B cells appear will prompt others in the field to re-evaluate and interpret their results in a new way," notes
Associate Professor Joan Yuan.

The idea of stratified development of the immune system is a long-standing theory: different immune cells emerge at different times during development to form the adult immune system
.
More specifically, for B cells, the exact time frame for the natural appearance of
the maximum wave during normal development is unknown.
To investigate how many B cells produced at different stages of life naturally remain in the body, the researchers used genetic tools to label and map
cells in the mouse model they developed.

By doing so, researchers can visualize the immune system based on time of development, link early life events to later life outcomes, and give them new insights
into how this might work in the human body.
Given that the immune systems of humans and mice follow the same guidelines, these insights are possible, allowing scientists to learn more about how individual genes regulate human health and disease
by studying mice.

"Together with researchers from Lund University's Department of Immunology, we found that many B cells in the gut are also produced in the early window after birth and remain in
adulthood.
They exist with microorganisms in a symbiotic way in which B cells respond to our gut bacteria, and the presence of bacteria also promotes the maintenance of these cells," emphasizes postdoctoral researcher Stefano Vergani
.

Speaking of B cells, the gut is home to a large collection of B cells and is the largest place
for antibody production in the human body.
However, the collection of these B cells remains somewhat mysterious compared to B cells in the lymph nodes or spleen, and the time frame in which they form was previously unknown
.

To better understand how these early life-producing B cells functioned, they introduced a mouse model of
rotavirus infection.
They found that when newborns were exposed to rotavirus, intestinal B cells produced antibodies that were different from
those produced by adults.

"Given the similarities in mammalian development, our findings suggest that, as adults, a large portion of our gut and elsewhere form
early in life.
" The first few days after birth may be the period
when our immune response is set to be long-term.
This means that early exposure to one antigen may determine our immune health trajectory, as well as our susceptibility to disease and allergies later in life," concludes
Joan Yuan.

The findings provide a better understanding of how B cells, or the immune system, are programmed early in life, opening many doors
to explore how microbial exposure and various infections program the long-term behavior of the human immune system.