This time on Science interrupted I’m going to talk to you about how my adventures in science were interrupted by my maternal antibodies. And why this is literally the coolest thing I have ever experienced.
But first, let’s set the stage a little. About a week ago, my daughter was at the doctor for her four-month checkup and her four-month vaccinations. One of the vaccinations she got was for rotavirus and this vaccination comes in oral form (which, way to go modern science, oral vaccines are WAY easier for my daughter to take - she literally giggled the entire time she was getting the vaccine). After we got home 10 minutes later, I did what I always do when my daughter is anxious/ annoyed/ upset/ tired/ hungry. I nursed her until she fell asleep and then I went on with my day. Then, essentially out of nowhere, I felt sick. Like sinuses-are-full, immune-system-in-overdrive, hit-by-a-virus-bus sick. I was flabbergasted. What in the world was happening? Then it dawned on me - my baby had an oral vaccination. Then she nursed, while some of the vaccine was still in her mouth. My immune system was reacting to the inactive virus in her mouth, and building antibodies to send to her to fight the virus off for her.
Sure, my immune system was overreacting, but this is the coolest overreaction of all time. My immune system is doing what it is supposed to do, mounting an immune response to protect my baby.
One of the coolest facts about motherhood and breastfeeding that we aren’t taught in school is that, while a mother is breastfeeding, her body responds to the infant’s nutritional and immunological needs. Not only is breastmilk a source of nutrition, but breastmilk also passes antibodies, microbes, and hormones onto the baby1–4. The hormones, microbes, and antibodies start setting up the baby’s biological systems to grow and develop.
But how does this happen? More fun facts! Fun fact number 1: Mammalian nipples evolved from an apocrine-like gland during the course of mammalian evolution5. At some point during our evolutionary history mammals had sweat gland-like structures on their chests that eventually evolved into nipples. Fun fact number 2: Human breasts are designed to not only produce milk but also to engage in retrograde milk flow6–9. Breasts are designed to absorb baby spit backwash (a cool term from Dr. Katie Hinde10) as a way to “see” what is happening in the baby’s body.
So basically, I got sick because my body thought my baby was sick. That is so cool (but also crappy because I totally felt like I had been hit by a bus).
But why are mother and baby’s immune systems designed to behave this way? One reason is that an immune system is costly to grown and maintain11 even for adults. But for babies, the energy they devote to building their immune systems can’t be used to grow their body or brain. This is the first of many tradeoffs that babies will face in their lives: invest in their immune systems (and future life) even if it comes with reduced growth now or invest in growing big now even if it comes with a less developed immune system later.
But babies have a hidden strategy that they can use to reduce the severity of this tradeoff -- get mom to do the heavy lifting by making your immune system for you (called immune programming12) so you can invest all of your resources into growing big and strong! There is mounting evidence that the benefits of breastfeeding can be detected long after breastfeeding has ended13–15, so it seems like babies really come out ahead in this tradeoff (note here - I’m not trying to push a “breastfeeding only” agenda here, just talking about some of the research that exists. There are many reasons why a mom might choose to formula-feed their baby, including that they just want to. In the end, a fed baby is the best baby). Mom’s spend all the time and energy acting as the baby’s immune system (including drastically altering the composition of breastmilk to respond to a sick baby16) until the baby is weaned and needs to rely on its own immune system (between 6 and 12 months15). If you are thinking to yourself “Wait a minute! That sounds like a potential area for genetic conflict!”, you are right my friend! While most of the research on genetic conflict in immune systems has looked in (non-human) adults between the sexes17, immune system development is an opportune area to look for the footprints of genetic conflict. In fact, I wrote about this as part of my comprehensive exams and hope to investigate genetic conflict over immune systems.
So, in about two months, my daughter will go back to the doctor for the next rotavirus booster. Will I try to be more cognizant of my potential immune response after the oral vaccine? Probably not -- if my immune system can help her develop immunity by making the antibodies for her, having a shitty day isn’t the worst thing ever.
Stay curious my friends,
In case you are interested, here are some of the articles that I read and thought about while writing this.
1. Mazzocchi, A. et al. Hormones in Breast Milk and Effect on Infants’ Growth: A Systematic Review. Nutrients 11, (2019).
2. van den Elsen, L. W. J., Garssen, J., Burcelin, R. & Verhasselt, V. Shaping the Gut Microbiota by Breastfeeding: The Gateway to Allergy Prevention? Front Pediatr 7, 47 (2019).
3. Hanson, L. A. & Söderström, T. Human milk: Defense against infection. Prog. Clin. Biol. Res. 61, 147–159 (1981).
4. Lyons, K. E., Ryan, C. A., Dempsey, E. M., Ross, R. P. & Stanton, C. Breast Milk, a Source of Beneficial Microbes and Associated Benefits for Infant Health. Nutrients 12, (2020).
5. Oftedal, O. T. The mammary gland and its origin during synapsid evolution. J. Mammary Gland Biol. Neoplasia 7, 225–252 (2002).
6. Ramsay, D. T., Kent, J. C., Owens, R. A. & Hartmann, P. E. Ultrasound imaging of milk ejection in the breast of lactating women. Pediatrics 113, 361–367 (2004).
7. Geddes, D. T., Kent, J. C., Mitoulas, L. R. & Hartmann, P. E. Tongue movement and intra-oral vacuum in breastfeeding infants. Early Hum. Dev. 84, 471–477 (2008).
8. Geddes, D. T. Ultrasound imaging of the lactating breast: methodology and application. Int. Breastfeed. J. 4, 4 (2009).
9. Geddes, D. T. et al. Tongue movement and intra-oral vacuum of term infants during breastfeeding and feeding from an experimental teat that released milk under vacuum only. Early Hum. Dev. 88, 443–449 (2012).
10. Breast milk & baby spit. http://mammalssuck.blogspot.com/2016/01/breast-milk-baby-spit.html.
11. Lochmiller, R. L. & Deerenberg, C. Trade-offs in evolutionary immunology: just what is the cost of immunity? Oikos 88, 87–98 (2000).
12. Laouar, A. Maternal Leukocytes and Infant Immune Programming during Breastfeeding. Trends Immunol. 41, 225–239 (2020).
13. Oddy, W. H. Breastfeeding protects against illness and infection in infants and children: a review of the evidence. Breastfeed. Rev. 9, 11–18 (2001).
14. Oddy, W. H. The impact of breastmilk on infant and child health. Breastfeed. Rev. 10, 5–18 (2002).
15. Jackson, K. M. & Nazar, A. M. Breastfeeding, the immune response, and long-term health. J. Am. Osteopath. Assoc. 106, 203–207 (2006).
16. Riskin, A. et al. Changes in immunomodulatory constituents of human milk in response to active infection in the nursing infant. Pediatr. Res. 71, 220–225 (2012).
17. Science X staff. Differences in immune responses create a genetic conflict between sexes. Phys.org https://phys.org/news/2018-08-differences-immune-responses-genetic-conflict.html (2018).