The Surprising Wisdom of a Newborn Immune System
Much like their brains, babies’ immune systems are quick learners, adapting to their environments from the word go.
But a recent study from Pitt researchers suggests that, immunologically speaking, go-time might actually start in utero, long before a baby is even born—a notion that turns textbook biology on its head.
Using advanced cellular and genomic analyses, Liza Konnikova, assistant professor of pediatrics in Pitt’s School of Medicine and a neonatologist at UPMC Children’s Hospital of Pittsburgh, studied the mucosal immune system by analyzing gut tissue taken from fetuses ranging from 14 to 23 weeks of age. Results of the collaboration between Pitt researchers and scientists from Tel Aviv University in Israel were published in the Nov. 4, 2019, issue of Developmental Cell.
The immune system is really two systems: innate and adaptive. The innate immune system is always present in the body and includes natural barriers like skin and dendritic cells. The adaptive immune system, as the name suggests, adapts to encounters with foreign pathogens, growing and learning as it meets new invaders.
“We had presumed there’d be some adaptive component” in the tissue examined, Konnikova says, “but most likely naïve, meaning it’s never seen an antigen before.”
She and her colleagues were thus surprised to find a significant number of B and T cells, the major cellular components of the adaptive immune system. More strikingly, most of the T cells belonged to what Konnikova calls the “memory pool,” responsible for remembering past pathogens to better protect against future attacks.
That finding suggests that the fetuses’ immune systems were exposed to pathogens, something that their mothers’ placentas are designed to prevent—and that researchers were not anticipating.
Konnikova and others have speculated that the fetuses may encounter molecular byproducts of pathogens through amniotic fluid. But right now, she says, they don’t have a clear answer as to how this could be.
“That’s the burning question.”
These findings raise the possibility of intervening to boost vulnerable infants’ immune systems before they’re even born, Konnikova says, perhaps through maternal vaccines. She pointed to necrotizing enterocolitis, a disease that affects the intestines of premature infants, causing serious inflammation that can lead to perforation and result in death. Bolstering the defenses of these infants’ intestines could be a lifesaver.
The paper also sheds new light on how the adult immune system forms, and when—it turns out that the architecture of adult mucosal immunity is set far earlier than previously thought.
By the end of the second trimester, most of the T cells researchers found were of the memory variety. Although significant changes still occur as the fetus becomes an infant and then an adult, Konnikova says, “the major components of the mucosal immune system in adults are already there in fetuses.”
Recent technological innovations made these findings possible. These include an approach known as CyTOF that uses sequencing processes in combination with mass cytometry, a measurement technique that tags antibodies with metal isotopes, allowing scientists to sort antibodies according to their mass. The methods used to collect and preserve the tissues are also novel.
“This work is really tricky to do, because you need human tissue,” Konnikova says.
As a postdoctoral fellow, she helped develop a technique of cryopreserving tissue that allowed the Pitt-based researchers to save fetal tissue across a range of ages.
“We realized we can save the tissues, and we have all these new techniques,” Konnikova says. “The way they’re storing these tissues opens up these possibilities.”
That includes the chance to delve even deeper into how, and when, the immune system develops.
“We’re just starting to do the work.”
Men and Women Express Depression Very Differently at the Molecular Level
By Jason Bittel
Scientists have long struggled to understand why incidences of major depressive disorder (MDD) are higher among women than among men. Pitt’s Marianne Seney has found biological evidence that the sexes might be vastly different in regard to this mood disorder.
Not only that, but by some molecular measures, they’re opposites.
Seney, an assistant professor of psychiatry, and her team looked at brain tissue taken from 26 deceased men and 24 deceased women with MDD and compared those samples to samples taken from an equal number of deceased men and women who did not suffer from MDD while they were alive.
The researchers measured the genes expressed by three regions of the brain that are involved in mood regulation. When they analyzed each sex, they found that of the 706 genes that showed altered expression by men with MDD and the 882 genes that showed altered expression by women with MDD, just 21 genes were altered in the same direction. At the same time, 52 other genes displayed expression changes in completely opposite directions when it came to men and women with MDD. Further, a sex by disease analysis revealed that more than 1,000 genes were changed in opposite directions in depressed men and women.
These findings suggest that, with the exception of just a few genes, MDD presents in the brains of men and women in vastly different ways at the molecular level.
For example, Seney’s team found that men with MDD had lower expression of genes related to synapse function. Conversely, women with MDD had greater expression in those same genes. And it was a similar story for genes associated with inflammation and immune function: Men had increased gene expression and women showed decreased gene expression.
These opposing pathologies were “super-surprising to us,” says Seney.
The possible implications for these findings underscore the importance of studying both men and women in drug development—something that might sound like common sense, but has not been the norm in the past.
In fact, the team wrote, “many previous postmortem brain analyses in MDD were performed in mostly (or only) men.” Seney says the reasons for this are many, but chiefly, it’s long been viewed that men’s brains are less complicated to study because men don’t have all the hormonal shifts women do. This has caused an enormous bias in medical research that is still being corrected. (For instance, it wasn’t until 1993 that the National Institutes of Health implemented a policy that sought to ensure that women and ethnic minorities were included as participants in clinical research.)
Just imagine that you’re learning about how the brain works, but you’re only studying men’s brains. Say you create a drug addressing a neurological change related to depression. Even if that drug works really well for men, it “might push women further into a molecular pathology and potentially further into depression,” Seney says.
The team’s results were first published in Biological Psychiatry in 2018. Next, Seney hopes to disentangle how some of the genes marked by the study relate to behaviors in living people. Someday, the research may also help bring precision medicine to patients with major depression, and the first step might be sex-specific treatment.
“Maybe in the future we could look at what symptom profile a patient fulfills and then use that to target the treatment,” says Seney.
A 60-Year-Old Drug Could Lengthen Life For Kids With Congenital Defects
By Erin Hare
Surgery can mend congenital heart defects shortly after birth, but those babies will carry a higher risk of heart failure throughout the rest of their lives. Yet, according to a Science Translational Medicine study published in October 2019 by University of Pittsburgh and UPMC Children’s Hospital of Pittsburgh researchers, β-blockers could supplement surgery to build infant heart muscle and mitigate the lasting effects of congenital heart disease.
“The question is no longer, ‘Can we save this baby?’” says senior author Bernhard Kühn, associate professor of pediatrics at Pitt and director of the Pediatric Institute for Heart Regeneration and Therapeutics at Children’s Hospital.
“The challenge for our young patients is that we want to enable them to have a long lifespan, ideally as long as a person without heart disease.”
For a congenital heart defect called tetralogy of Fallot, treatment typically involves surgery at around 3 to 6 months of age, which is incidentally when heart muscle cells—cardiomyocytes—are at peak production. Decreased heart function during the first few months may be causing these infants to miss an essential opportunity to build heart muscle.
Kühn’s team collected heart tissue from 12 infants who underwent corrective surgery for tetralogy of Fallot and found that more than half of the cardiomyocytes in these samples had started to divide but then got stalled midway through the process; something similar happens with conjoined twins. The ultimate result was fewer cardiomyocytes overall, which makes the heart more vulnerable to damage later on.
“By the time our surgeons operate on these patients, the horse is already out of the barn,” Kühn says. “Our data show that they have up to 30% fewer cardiomyocytes than a normal infant has at this age. That’s significant. To put that in context, an adult’s heart attack can destroy up to 30% of cardiomyocytes.”
Through a series of experiments in human and mouse tissue, the researchers traced this cell division failure back to β-adrenergic receptors.
The natural next step was to ask whether the β-adrenergic receptor blocker propranolol—a common blood pressure medication—could enable proper cell division in infants with congenital heart defects and improve heart function.
Indeed, in the heart tissue samples taken from infants with tetralogy of Fallot, the medication enabled dividing cells to separate properly.
And in mice, propranolol treatment during the first weeks of life allowed for better recovery from heart attacks in adulthood. Compared to untreated controls, mice that were given propranolol as pups retained 30% more cardiomyocytes and were able to eject 24% greater blood volume following a heart attack. The treatment did not affect heart function.
According to Kühn, having such promising results with a tried-and-true drug like propranolol means the pathway to clinical translation could be relatively quick.
“This all comes together in a very applicable way,” Kühn says. “Propranolol was synthesized nearly 60 years ago, so we’re able to bypass a lot of the groundwork that would have to be done if we had identified a receptor that doesn’t have a drug for it.”