Fighting foreigners prevents self-destruction

Intimacy is a cellular turn-on he simple act of coming closer together ignites signaling pathways in epithelial cells, as shown and colleagues. The results describe how cells might activate cellular responses to T mechanical stress. Cells are pushed closer together by physical forces. In the lung, for instance, epithelial cells feel the pressure from underlying muscle tissue, particularly in asthmatic patients. The authors see that these forces do not change cellular volume. Rather, they squeeze out fluids from between neighboring cells. The resulting close cellular proximity means that ligands that get secreted between cells are more concentrated and therefore more likely to activate signaling pathways. " Now there's less hildren everywhere rejoice—there may be such a thing as being too clean. According to and colleagues, over-protection from exposure to germs might cause autoimmune diseases. Autoimmune diseases, including rheumatoid arthritis and lupus, are generally thought to result from an overstimulated immune system. This assumption does not, however, explain why these diseases are more prevalent in sterile western societies or why they often correlate with depleted numbers of T cells. Sarvetnick and colleagues now show that the combination of a depleted and understimulated immune system leads to autoimmunity. The authors find that a mouse model of autoimmune diabetes has just this combination. These mice make too much of the IL-21 cytokine, which promotes proliferation (like other cytokines) but not survival (unlike other cytokines). Thus, their T cells continually multiply but never fill up the immune system. These rapidly multiplying T cells (which likely respond to self-antigens from nearby organs) caused autoimmune diabetes. But diabetes was prevented if the mice were injected either with enough T cells to fill the immune system or with bacterial proteins so that multiplying T cells expanded robustly to these non–self-antigens. C " Most people do not want to think of autoimmunity as a form of immunodeficiency, " says Sarvetnick. But T cells in sanitized western children might be faced with a problem: without enough stimulation by foreign antigens to prompt T cell expansion, the T cells that do fill the immune system may have more than the normal share of autoreactive clones. So a bit of play time in the dirt might serve kids well. ᭿ Autoimmunity (filled circles) is prevented if mice are given doses of T cells to fill their immune systems. space for these things to bounce around in before they find a receptor, …