The human immune system has many different types of cells which form a well-organized and well -armed force that has the ability to combat almost any bacteria or virus which is trying to gain access to our bodies. Among its ranks, the immune system has an elite fighting force composed of T cells, members of a group of white blood cells known as lymphocytes, which plays a vital role in cell-mediated immunity. Cell-mediated simply means that unlike B cells which can secrete antibodies to target bacteria and viruses at a distance, T cells need to get up close and personal when dealing with pathogens. More specifically, T cells are involved primarily in combating viruses by using various mechanisms including target host cell killing and phagocytosis of free floating virus particles.
The chief mechanism used by T cells to combat various infections involves utilizing their unique T cell receptors (TCRs). These receptors allow T cells to identify specific foreign entities and eliminate them from the body. In order to accomplish this task, T cells must first be presented with a piece of the pathogen known as an antigen which can bind to the TCR. Depending on the tightness of the fit, or the affinity of the interaction, the TCR will either trigger the T cell to become activated or it will remain senescent. Due to the specificity of this interaction, the T cells which are generated are geared to combat specific pathogens. This in turn lays the foundation for an adaptive immune response.
Adaptive immunity is the part of our immune system which kicks in after an infection has bypassed our innate defenses such as our skin, the mucous in our nose, or the many white blood cells which combat pathogens nonspecifically. This type of immunity is adaptive because it produces a highly specialized response against a particular pathogen after the pathogen has already entered our bodies. In order for T cells to participate in an adaptive immune response they first must make the transition from a naïve T cell, which is one that has not interacted with a specific antigen, to a mature T cell, one that has contacted an antigen. The transition of a T cell from naivety to maturity is an area studied by Rashmi Kumar and her colleagues, and their findings were recently reported in the journal Immunity. Specifically, they examined the difference between T cell receptors (TCRs) on naïve and mature T cells in the hope of discovering the reason why memory T cells respond more rapidly and robustly when confronted with an antigen than do naïve T cells. A rapid T cell response is important for adaptive immunity because it allows for memory T cells, those that continue to circulate in our blood after an infection, to jump into action should the same pathogen try to infect a person twice.