The surprising players of the immune system that can cultivate bacteria

Throughout the day After infection, the researchers sampled the amount of salmonella bacteria in the spleen of the infected mice. Analysis of the data indicated a clear trend: in the first eight hours of infection, the bacterial load decreased, but then there was a surprising reversal: the bacterial population began to grow, and later to really thrive, leading to the death of the mice within a few days.

Macrophages, found in almost every tissue, can exist in several different configurations, the differences between which are very subtle. Using an advanced genetic analysis method – RNA flooring at the single cell level – Hoffman was able to differentiate between three different populations of macrophages in salmonella-infected mice. One of them is a population of macrophages that has not yet been characterized. The discovery was particularly surprising, as this unfamiliar population grew with the progression of the infection, and when the researchers compared the amount of intracellular bacteria between each of the macrophages, they found that the newly identified macrophage serves as a habitat where the bacteria multiply and thrive. “We found the culprits in the surprising increase in the bacterial population,” Hoffman notes. “Now it remains for us to try to understand what their motives are.”

Macrophages neutralize toxic compounds that release the immune system

Active cells of the immune system release into their environment toxic compounds for bacteria. Beyond a certain level, however, these compounds can be toxic to both the cells themselves and other cells in the environment, thus causing tissue damage. The researchers found that macrophages of the new type they discovered could neutralize these compounds, presumably to protect themselves, as well as perform damage control on immune system function. However, the chemical process of neutralizing the compounds produces a carbon source available to intracellular bacteria such as salmonella. In other words, the macrophages identified in the study inadvertently turn into an all-you-can-eat buffet that is especially inviting to salmonella. To test the hypothesis, the researchers infected engineered mice that could not produce this type of macrophage, and found that they were indeed more resistant to salmonella.

” The immune system, but the bacteria take advantage of this to enter the cells in the back door, “Hoffman explains. These findings pave the way for a deeper understanding of the course of bacterial infection and break new research directions on the survival strategies of intracellular bacteria of different types and in different body tissues. Dr. Avraham adds: “We have the first evidence that this subspecies of macrophages also exists in health and may play a role in the survival of a bacterium that causes tuberculosis.”

Gili Rosenberg, Leah Weinman, Arie Solomon, Dr. Shelly Chen Avivi and Dr. Noa Bosel Ben-Moshe from the Department of Biological Control and Sebastian Trezbansky from the Department of Immunology at the Weizmann Institute.

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