RATS: Humanity's Greatest Supervillain

Talk about rat's immune system/disease vector

In movies, books and even in real life, rats are depicted as a pest. In other words, one of humanity’s greatest villains. From rats directly, diseases such as Hantavirus Pulmonary Syndrome, Leptospirosis, Rat-Bite Fever, etc can be deadly to humans ( CDC, 2017). Indirectly (using a vector like flea or termites) rats can still infect causing plagues, scrub typhus, lassa fever, etc ( CDC, 2019). For an animal that can make many people/animals sick, surprisingly, a rat’s own immune system could be one of its greatest weaknesses.

The immune system is a very important physiological aspect of a being. Given the limited energy, rats have to sub-maximize their immune systems, which makes them susceptible to many bacteria and diseases. Resources also play a factor in how well their immune system can fight off diseases and contribute to immune heterogeneity (Viney & Riley, 2017). In an experiment, wild rats’ immune systems were compared with laboratory rats’(unlimited resources/more energy/similar to humans) immune systems. Wild rats produced a larger amount of CD4+ cells as well as dendritic cells, macrophages and natural killer cells. Wild rats had a rapid expression of IL-2 receptor by NK cells, which allowed them to possibly produce more IFN-γ (Viney & Riley, 2017). IFN-γ is responsible for innate and adaptive immunity. They were also better at making antibodies, such as IgG, IgE (Viney & Riley, 2017). Although wild rats’ immune systems are in a highly antigen-experienced state, they were not able to produce as many cytokine responses as laboratory rats.

Another surprising reason why their immune system is compromised is because of constant exposure to ammonium perfluorooctanoate, which is a chemical commonly used by humans to provide corrosion and chemical resistance. A study showed that ammonium perfluorooctanoate is responsible for weakening their immune system. It is very toxic that they start to lose weight, produce more corticosterone, decrease IgM production, decreased spleen and thymus weights and cell numbers and microscopic depletion/atrophy of lymphoid tissue (Loveless et al., 2008). Their immune system is one of the biggest reasons why they have a life span of one to two years.