Immune System to the Rescue!

Hey guys! It's Burt back again with another exciting post. Sorry it’s been a while! I’ve been busy taking care of Toni as she has been sick for the past few weeks. I hope you all have been able to stay healthy during the COVID-19 pandemic. Surprisingly, we get sick just like humans, although our response to a pathogen is a bit different. You see, our immune systems are split into two types of responses; innate and adaptive. Innate immune responses are the body’s general immediate response to a pathogen, while the adaptive response works more slowly and is more specific. This means that adaptive immunity mounts responses that are specific to the type of pathogen attacking the body while the innate immune response generally fights pathogens the same way regardless of the type or class of pathogen threatening it. If we compare innate and adaptive immunity to COVID-19, the innate response would be similar to the first responders, like doctors and nurses that work extremely hard to treat patients, while the adaptive response would be comparable to a vaccine deigned to specifically protect the body from the virus.

Because innate immune responses are more primitive, they are more similar between fishes and mammals like humans. Most of the innate responses are identical between us! On the other hand, adaptive immune responses are somewhat different between fishes and mammals. One major difference between our adaptive immune responses is that we, fish, don’t have lymph nodes which are a part of the lymphatic or secondary vascular system. The lymphatic system is responsible for draining fluids from organs of the body.  Blood vessels of the scientists that study us sometimes leak fluid into their organs as blood circulates throughout the body. To prevent the buildup of fluids, their lymphatic system takes the accumulated fluid, and filters it in lymph nodes before introducing it back into the bloodstream. Because this fluid can contain pathogens that reside in tissues throughout the body, mammalian lymph nodes contain immune cells that contact and fight against these pathogens. Instead, Toni, Tyrone, me, and all of our fish cousins have clusters of cells in our spleens called melanomacrophage centers (say that 3 times fast!) that scientists believe have similar functions to their lymph nodes.

Another major difference in the immune response between fishes, like Toni and I, and mammals is that fish do not have bone marrow. I know, it’s so strange! In mammals, bone marrow is where immune cells are made. In us, our immune cells are generated in the anterior portion of our kidneys, in an organ called the head kidney, located, well, as you can guess, in our heads right behind our super smart brains!  

So, Toni’s spleen and kidney have been working overtime to fight off her infection and assure that she stays safe and healthy before we let her out of quarantine! If you are interested in learning a little more about the differences between the immune response in fishes and mammals, check out the papers below. Then be sure to check back here in the future for more details on how the scientists are specifically studying our immune systems! 

Lieschke, G. J. and N. S. Trede (2009). “Fish immunology.” Curr Biol 19(16): R678-682.

Steinel, N. C. and D. I. Bolnick (2017). “Melanomacrophage Centers As a Histological Indicator of Immune Function in Fish and Other Poikilotherms.” Front Immunol 8: 827.