Decision letter: Gamma delta T cells recognize haptens and mount a hapten-specific response

Abstract

Our immune system responds to invading microbes—such as viruses and bacteria—and tries to eliminate the threat via two distinct but connected systems: the innate and the adaptive immune systems. Cells of the innate immune system patrol our organs and tissues in an effort to identify and eliminate threats with a quick but general response, which is similar for many different pathogens. This first line of defense also escalates the immune response by activating the adaptive immune system. Unlike the innate immune response, the adaptive immune response targets unique molecules of different sizes, shapes and chemical compositions—ranging from small organic molecules to large pathogens. The adaptive immune system consists of three types of immune cells: B cells, alpha beta (αβ) T cells and gamma delta (γδ) T cells. These cells have proteins on their surfaces that function as receptors; when the receptors recognize and bind to a foreign molecule (called antigen), the cell becomes activated. This then triggers a cascade of events that help to clear the infection and help immune cells to rapidly respond to any future infection by the same pathogen. αβ T cells and γδ T cells respond to different triggers, but perform similar tasks—while B cells perform tasks that are different from those of T cells. An effective immune response often involves both B cells and T cells. One important way that the adaptive immune system can identify an invading microbe or monitor for damaged or abnormal cells is by recognizing chemicals produced by pathogen and chemical modifications of host molecules. And while B cells are able to do this, αβ T cells are not. Zeng et al. now show that γδ T cells can also recognize and mount response against this type of antigen. γδ T cells were shown to detect both a small synthetic fluorescent dye, and a chemical modification that has been extensively studied for B cell responses over the last 80 years. Following on from these findings, the next challenge is to identify γδ T cells that recognize molecules or chemical compounds produced during infection or disease, and to define these cells' role in immunity.