The club - what do cells of the immune system do in selected meeting places in the bone marrow?

Select "clubs" found in the bone marrow are meeting places for different types of immune system cells

If you want to meet the right people, it is important to be in the right place. This rule also seems to be true for certain cells of the immune system. A recent study conducted by Weizmann Institute of Science scientists showed that select "clubs" found in the bone marrow are meeting places for different types of immune system cells. For some cells, these places are sites of unique activities, but for others, encounters there can be a matter of life and death. Prof. Idit Shahar and Dr. Stefan Jung, from the Department of Immunology at the Weizmann Institute of Science, discovered the importance of location while researching the activity of unique cells of the immune system called dendritic cells, which

constitute one of the body's primary lines of defense against microscopic invaders. These "watchers" are found in small amounts in all body organs, especially in places like the skin and the stomach - through them disease-causing microorganisms such as bacteria enter the system. When these "border guard" cells encounter invaders that could harm the body, they engulf them and display the identifying parts on their outer membranes, like red flags, to alert the rest of the immune system to deal with the threat. Together with research student Anita Spozhnikov and Dr. Yael Pevzner-Yung from the same department, the scientists studied a group of dendritic cells that exist in the bone marrow. Despite the fact that only a small amount of these cells are found in the bone marrow, the scientists, together with Dr. Wietz Slav Kalashenko of the Department of Veterinary Resources, noticing the fact that dendritic cells preferred to stay in certain areas, And they had a tendency to gather in "chambers", or alcoves, which are located near the blood vessels that cross the bone marrow, a finding that suggests that these alcoves play an important role in protecting the body against disease agents.

The same observations led to another finding: the dendritic cells gathered in these niches, as did B and T cells, which are the "special forces" of the immune system. Using in vivo methods that Dr. Jung had developed earlier, the scientists eliminated the dendritic cells. These cells then stopped appearing in the niches.

Did the dendritic cells somehow attract the B cells to their meetings? Or did, as Dr. Jung and his team hypothesized, the dendritic cells function within these microenvironments to keep the B cells alive? B cells, like many cells of the immune system, are relatively short-lived, and they are constantly On a tightrope between survival and self-destruction, the researchers believed that dendritic cells help B cells stay alive within their niches, to ensure that there is always a sufficient supply of B cells available for the need. The body's defense against the attack of various disease agents.

To test their theory, they injected mice with special B cells with enhanced survival skills. With or without dendritic cells, the enhanced B cells reached niches in the bone marrow and remained there - proof that they joined the "club" of the immune cells on their own, without the need for a special invitation. It turned out that encounters between the two types of cells were essential to keep the normal, vulnerable B cells alive. But what really happened "behind the doors" of the alcoves in the skeleton? To try to find out the answer, the researchers created two strains of mice through genetic engineering. Each strain was missing one of two molecules that the scientists had identified as possible factors for B cell survival. The results showed that only one of these factors, a molecule called MIF, actually worked to extend the life of the B cells.

It turns out that this molecule transmits a signal to the B cell, which causes it to postpone its suicide plan, thus prolonging its life.

"This study," say Prof. Shahar and Dr. Jung, "has several possible consequences. First, it sheds new light on the role of bone marrow in the body. Today we know that bone marrow is not only the supplier of blood cells and cells of the immune system, and that it is also an important site for the activity of the immune system. Additional studies may reveal, in the future, ways to increase this activity, which could function as a backup, for example, in cases of damage to other sites where immune activity occurs."