When you have a chronic allergic disorder, it’s easy to blame the trigger — an early pollen season or furry pet — but the real culprit is your own immune system. Designed to attack foreign substances such as bacteria and viruses, T cells are the immune system’s watchdog to recognize serious threats. But sometimes T cells can be too zealous and set in motion a signaling cascade that can cause allergic reactions to everyday things and even attack your body’s healthy cells by mistake.