Scientists have found an alternative track for potentially aggressive T-cells in which the cells can be recruited to help "police" over-active immune responses via the molecule CD, instead of leading to autoimmune disease.
The immune system keeps us healthy by avoiding responses that are too lax or too extreme (eg, people get sick if their immune system inefficiently battles pathogens such as bacteria and viruses, and conversely, if their immune system is too robust, they may develop autoimmune diseases).
Daniel Hawiger, MD, PhD, assistant professor of molecular microbiology and immunology, Saint Louis University, and colleagues from his lab had a breakthrough in understanding how regulatory T cells (which police other T cells' responses) develop. T-cells, the immune system's soldiers, recognize between self and nonself.
During the T-cell "learning" process, a group of them always develops that remain self-reactive. They could foist their attacks on the body's own cells, which can lead to autoimmune diseases. "There is a need to keep those T-cells in check, because otherwise we would have a runaway immune system," Hawiger says.
The immune system generally keeps self-reactive T-cells under control by deleting them. But, some of them may be useful for the immune system in recognizing foreign pathogens. The molecule CD5 helps these self-reactive T-cells survive and stay under the radar.
The researchers discovered that increased expression of CD5 also serves as a safeguard against autoimmunity by training potentially auto-aggressive cells to become regulatory T cells, lessening the risk of autoimmune disease. "What we discovered is that there is a mechanism that can specifically push those self-reactive T-cells to become ‘T-cell policemen,' " Hawiger says. "They become T-cells that can regulate other T-cells' responses."
The article "CD5 Instructs Extrathymic Regulatory T Cell Development in Response to Self and Tolerizing Antigens" is published in the March issue of the journal Immunity.
[Source: St Louis University]