Newborns make their way into the world and are immediately susceptible to infections. Protection is provided by antibodies that are transmitted vertically from the baby’s mother, either through the placenta in the wombOr via breast milk after birth, until the baby’s immune system develops.
Understanding how maternally transmitted antibodies protect newborns has been a primary research focus in neonatal studies. Previously, antibodies were considered Just Target of pathogens that occur outside cells. However, many pathogens survive by intracellular replication, including group B streptococcus (GBS), Escherichia coliAnd the Listeria monocytogenes and Epstein-Barr virus (EBV).
Whether or not vertically transmitted maternal antibodies can protect against endogenously reproducing pathogens has remained a major unanswered question for the field. Now, a new study has been published in temper nature This query sheds light.
A research team led by Dr. John Erickson, MD, associate professor of neonatology, Cincinnati Children’s Hospital Medical Center, discovered that a “small change” in the structure of polysaccharides that bind to antibodies during pregnancy could protect them against a variety of pathogens—including Including those that reproduce inside cells.
The researchers say these findings could not only pave the way for new targeted therapies for expectant mothers and children, but could also influence the field of antibody-based therapies in general.
technology networks I had the pleasure of interviewing Ericsson to learn more about how the study was conducted, its main findings, and the research team’s next steps.
Molly Campbell (MC): Can you discuss the rationale behind this research study, based on previous understanding of maternal antibodies/antibodies?
John Erickson (JE): It has always been appreciated that mothers pass both antibodies on to their children in the womb – Cross the placenta – and after birth via breast milk. This provides an important layer of immune defense for newborn babies as they are highly susceptible to infections. In fact, approximately 50% of deaths in children under 5 years of age occur in neonates less than 28 days of age, and a significant portion of these ~2.5 million deaths annually are caused by bacteria and viruses that lead to sepsis, pneumonia or diarrheal disease.
A notable limitation of antibodies is that they are believed to target pathogens only when they are extracellular (ie extracellular). But many of the pathogens that cause this serious neonatal infection have an intracellular life cycle (that is, they prefer intracellular reproduction), where antibodies are not readily accessible. Therefore, a major unanswered question in this field is whether maternally transmitted antibodies can protect against the myriad of intracellular infections affecting neonates.
we used Listeria monocytogeneswhich have an exclusive intracellular life cycle and cause serious infections in pregnant women and newborns, to determine if vertically transmitted maternal antibodies can protect against neonates Listeria infection. We were fascinated to find that ListeriaSpecific antibodies obtained from pregnant, but not virgin, mice provide strong protection against them Listeria Infection in newborns. This told us that antibodies can indeed protect against intracellular infections but was only demonstrated by studying immunology in the context of pregnancy. Previous attempts to study antibodies against Listeria Focused on adult animals only, so moving these studies into a more physiologically related reproductive context enabled this intriguing discovery, which has important implications for ongoing measures to reduce the staggeringly high global mortality rate of neonates.
MC: Your study shows that pregnancy changes the structure of polysaccharides bound to antibodies, enabling mothers to protect their babies. can you explain How This structural change achieves this?
J.E.: The change that occurs is incredibly subtle. We deciphered the molecular switches that occur through a long process of elimination. We first excluded the usual changes that could occur with antibodies, such as the different isotypes and their binding properties. We then concluded that the change must occur after translation, that is, after antibody production, given that the pregnant mice were able to convert the pre-existing antibody to this new protective form.
The most common modification of antibodies involves the sugars attached to them, which is called glycosylation. At first glance, the general sugar pattern on the antibodies from virgin and pregnant mice appeared identical. But we were struck by an unusually high amount of sialic acid, which is generally believed to be the last step in glycosylation of antibodies. We decided to remove sialic acid from the normally protective antibodies of pregnant mice and found its ability to reduce Listeria The disease is completely gone. We then used a “glycoengineering” approach to remove sialic acid from Listeria Antibodies from virgin mice, then standardized re-release of sialic acid, resulting in protection against Listeria When transferred to neonatal mice. We therefore concluded that a molecular variant of sialic acid must be present in the pupal state that prevents the antibodies from being able to protect against Listeria Infection in neonates.
Minor changes ended up with acetylation of sialic acid on the antibodies. During pregnancy, an enzyme called SIAE is upregulated in both mice and humans, and this enzyme catalyzes the deacetylation of sialic acid. Acetylation is a very simple change: it is the addition of only six atoms! However, these six atoms prevent the recognition of the acetylated transcript of sialic acid by a specific receptor of sialic acid on neonatal B cells – called CD22 – which is essentially an “off” switch on certain subsets of B cells, in particular the subset of sialic acid. A large amount of the IL-10 inhibitor cytokine.
Antibodies from virgin mice possessing the acetylated version of sialic acid are unable to bind to CD22 on B cells, and thus cannot turn off these IL-10-producing B cells. IL-10 continues to inhibit other immune cells, greatly enhancing the susceptibility of newborn mice to Listeria infection. For antibodies from pregnant mice that have deacetylated sialic acid, they are then able to bind to CD22 and turn off IL-10, which greatly reduces the sensitivity of neonates to infection with Listeria infection.
MC: Can you discuss the applicant? mass spectrometry techniques (and other methods) you used to determine the biochemical differences between antibodies in virgin mice compared to pregnant ones?
J.E.: We first used proteins called ‘lectins’ that bind very specific carbohydrates, which are added in unique ways to other sugars. For example, we used Pacific crab-type lectins, as well as a virus that mainly affects pigs, both of which are known to bind specifically to the acetylated version of sialic acid. These lectures confirmed our suspicion that Listeria The antibodies from virgin mice possessed more of the acetylated version of sialic acid.
Next, we reached out to our great partners at the University of Georgia’s Center for Complex Carbohydrate Research, because of their extensive experience with advanced mass spectrometry techniques. They used a unique approach to attach a plate of known ions to variants of sialic acid and confirmed it Listeria Antibodies from virgin mice possess approximately ten times more acetyl sialic acid than antibodies from pregnant mice.
MC: Can you outline the major approaches adopted in this study?
J.E.: The main approach we used was to explore immunology through the lens of pregnancy, in which the immune systems of mother and child are uniquely intertwined. This enhanced our ability to detect very subtle, but very important, changes that help protect newborns from dangerous infections.
Once we showed that mothers could pass on protection to children from particularly nasty bacteria that were thought to avoid this type of protection, we then used genetically modified mice to confirm which part of the immune system was responsible.
This revealed to us that antibodies can perform a new function that researchers previously thought was not possible. Time, collaboration, and advanced immunological and biochemical techniques revealed a small molecular change in the polysaccharides bound to the antibodies. These studies reveal that mothers already know better, even about producing the best antibodies to help protect their babies.
MC: This study determined that the “acetylated” form of sialic acid (a sugar bound to antibodies) converts to the “deacetylated form” during pregnancy. Is sialic acid usually in acetyl form? Why does this shift occur in pregnancy?
J.E.: The amount of acetylated sialic acid varies with tissues. In general, though, acetylcysteine is usually uncommon and makes up a small percentage of the total sialic acid pool. Prior to our study, the occurrence of acetylation on antibody-bound sialic acid was not known, which makes this one of the astonishing findings of our research paper.
how exactly Listeria The infection generates antibodies carrying acetyl sialic acid which will be the subject of future study. We believe that pregnant women regulate the enzyme responsible for deacetylation in order to enhance the protective ability of the antibodies that will be passed on to their babies. This would represent one way to improve ‘reproductive fitness’.
MC: You say that “changing the antibodies that occur naturally during pregnancy can be replicated to change how the antibodies stimulate the immune system, ‘tuning’ their effects.” Please, can you elaborate on how to achieve this?
J.E.: The scientific community and the biopharma industry have become adept at producing antibodies for a variety of purposes, but increasingly to treat specific conditions, such as cancer, autoimmunity, and infections.
However, based on our data, there is an amazing untapped potential in the ability to modulate the way these antibodies act by altering the binding to glycosylation – antibody-bound sugars. Our findings suggest that even a very small change, such as acetylation of terminal sialic acid residues on antibodies, can significantly affect their functions.
MC: This research has mostly been done on animal models. Can you discuss how you expect it to translate to humans?
J.E.: You are correct that most of this work has been done in animals, allowing us to specifically manipulate the immune system and glycobiology to identify this fascinating new mechanism of antibody protection.
More animal work is needed to explore the ways in which these unique antibodies are generated and how they also help protect children. However, we showed in our paper that the key enzyme regulating antibody acetylation, SIAE, is increased in both mice. And the Human immune cells during pregnancy. This major finding links our findings in mice to human pregnancy. It will be important to ensure that antibodies in humans also possess this unique version of sialic acid which decreases during pregnancy.
MC: Are there any limitations to this research that you’d like to highlight?
J.E.: For decades, the field of immunology has believed that antibodies play a very limited role in protecting against intracellular pathogens. The early studies that made this determination used Listeria To show that transfusion of immune serum containing Listeria The antibodies, which failed to protect the recipient mice, while the immune cell transfer was able to protect the recipients. We turned this on its head by considering the reproductive and developmental context where antibodies can actually protect against this exclusive intracellular infection. Future work will determine whether this approach applies to other intracellular infections, or in other contexts where it may be beneficial to target something within a cell.
Dr. John Erickson, MD, was talking to Molly Campbell, senior science writer at technology networks.