Ants & lions, immune system & ageing, stress & bacteria in the intestine | Last Week in Science (28th Jan 2024)

The ants and the lions

The old moral story of how small ants can fight off an animal as huge as an elephant was true in the forests of Kenya until big headed ants started showing up. Scientists observed that the big head ants started to kill the native acacia ants which would have saved the acacia trees from being eaten up by the elephants.

You must be wondering how elephants getting more food to eat can affect the lions.

These acacia trees provide hiding spots to lions for hunting zebras. The absence of acacia ants, increased grazing of acacia trees by elephants that decreased the tree cover. Scientists at Wyoming University studied number of zebras in areas where big head ants had invaded comparing it to areas where they had not invaded. They also looked at how many zebras got killed in these two different regions. They also tracked the movement of lionesses in these different regions by bugging them with GPS.

After three years of tracking, the result was as the trees started getting less dense, creating more open space, the lions had trouble in hunting zebras. So, the lions started hunting buffaloes. But how can that be a big deal? For one it takes lions more energy to hunt buffaloes and at times the lions get killed in the process. Second, the increase in zebras could cause unexpected changes to the existing ecosystem of the forests in Kenya.

This study is a beautiful example of how one small change in the ecosystem can have big effects. 

Can we use the immune system to slow ageing?

Our immune system have a specific type of cells called as the T cells which are trained to recognize specific cell types - pathogens or infected cells. With the recent advances, these T cells can be trained outside the body to recognize other types of cells - like cancer cells. These trained cells are called as CAR-T cells for chimeric antigen receptor T - cell. These T cells recognize specific molecules that are present on the surface of a specific cell type.

The aged and defective cells are called as senescent cells are the ones that have stopped growing and dividing because of damage. These cells usually release signals to call immune system to destroy them and are important for preventing cancer and causing healing after injury. The senescent cells increase in different tissues as we age. Their removal becomes less effective because of the decline in the immune system as we age. In the recent study, scientists at Cold Spring Harbor Lab generated CAR-T cells to recognize aged cells of mice. What they found was when these CAR-T cells were introduced in aged mice then they prevented some of the diseases that come with ageing or because of consumption of high fat diet. These mice were also physically more active after this one time treatment.

But it still remains to be seen whether it can prolong life and whether we can use such an approach in humans.

Reference: The fountain of youth is … a T cell?

Stress and the bacteria in the intestine

We all have heard examples of how stress can upset one's stomach. In severe cases, a disease called as Inflammatory Bowel Disease (IBD) is seen with stress that persists for a long time - called as chronic stress, which causes swelling of the intestines, stomach pain, and diarrhea. 

In the recent study, scientists at China Pharmaceutical University found that when mice were given chronic stress, for 2 weeks, they could not produce enough cells in their intestines to protect from infections and so causing swelling or inflammation. A specific type of bacteria of the Lactobacillus genus was found to be increased in their gut. These bacteria produced a chemical - indole-3-acetate (IAA). This chemical did not let the stem cells of the intestine to form the cells that would have protected the gut from infections.

What is interesting is scientists also found Lactobacillus and IAA in feces of humans who have depression. The scientists could treat the mice by giving a chemical called as alpha ketoglutarate. But it will still take time to see whether the same treatment would work in individuals suffering from inflammatory bowel disease or not. 

The scientists are still seeking answers to how the brain affects the bacteria in the intestines. These answers will help in understanding and treating many diseases that happen because of stress.