Our immune systems begin developing long before we are born. Immune cells are generated around 4-weeks after gestation and continue to grow while in utero. As a result, we are protected from infection and invading pathogen until we are born. Newborn infants are then exposed to new antigens and external stimuli in which the immune system must then quickly respond for protection. Interestingly, the mother’s antibodies in the baby are still active and can last months in the newborn to provide protection. Immune system development is fully matured 7-8 years later.
Once the immune system is fully developed, it can protect us from various pathogens by eliciting two separate responses. The first response includes the innate immune system that acts as the first responder. This initial barrier to protection is non-specific and general. More specifically, immune cells throughout the body, including neutrophils, macrophages, eosinophils, and basophils, circulate and survey the body for anything different occurring. If these cells detect an infection, the innate immune system is activated and those cells traffic to the site of infection. This response is effective as maintenance but cannot always completely eliminate diseases from the body.
To successfully clear out tissues of infection, our body employs another system known as the adaptive immune response. The adaptive arm of the immune system is more specific and can generate a stronger reaction to disease. In this case, the adaptive system orchestrates cells known as T cells and B cells to target the infection through direct contact or antibody production, respectively. T cells are generated in the thymus and despite our understanding of immune cell biology, we are still unsure about the mechanisms that drive early immune system development. Previous work has demonstrated the complexity of studying such early processes. However, the advancement of technology and the ability to study animal models helps scientists improve their understanding of fetal development, which has the potential to enhance therapeutics and better treat women and unborn infants.
A recent paper in Nature, by Dr. Sarah Teichmann and others, reported that immune cell development occurs a lot earlier than previously thought. Consequently, Teichmann and the team were the first to create a spatial atlas of the human thymus, which is responsible for training immune cells to target infection and disease. Teichmann is a Senior Group Leader at the Wellcome Sanger Institute in Hinxton, England. Her work focuses on processes that regulate gene expression and alter cell function. Her most recent work is part of the international Human Cell Atlas (HCA), which was established to map each cell of the human body. The overall goal is to better understand human health and improve patient diagnosis and treatment.
While the thymus helps generate immune cells to fight infection, it can also weaken immunity and cause autoimmune disorders. Therefore, Teichmann and her team set out to learn more about thymic development. The group tracked thymic immune cells from 11-weeks post-conception through three years of age. For the first time, the team found that the basic structure of the thymus is generated 12-weeks post conception. The team also found different subtypes of immune cells as well as locations within the thymus where these changes took place. These findings have major implications on our current understanding of immune cell biology and thymic development. This work also improves our knowledge of the thymus and provides information to better generate therapies for autoimmune disorders and other immune cell-related diseases.
Paper, Nature, Sarah Teichmann, Wellcome Sanger Institute, HCA