Help in Understanding New Kinds of Helpers

摘要

A single topic occupying four of the Top Ten places (with a fifth hovering just outside at #12) indicates something rather special afoot. That something is the scramble to understand a relatively recently identified component of the immune system, the T_H17 helper cell, which is specially adapted to fighting bacterial and fungal diseases. It is also implicated in autoimmune disorders such as inflammatory bowel disease, psoriasis, and rheumatoid arthritis.rnFor the past 35 years or so immunologists have considered two basic kinds of T helper cells in the immune system. T_H1 and T_H2 cells are classes of white blood cell that are not themselves capable of destroying invading pathogens. Instead, they are activated by exposure to antigens and are the core of the immune system's memory. T helper cells recruit and activate the cytotoxic cells, also known as T killer cells, that actively dispatch the pathogens. During their differentiation from na?ve T cells, T_H1 and T_H2 cells produce cytokine trigger molecules that prod other na?ve cells down the T_H1 or T_H2 development pathways, an autocrine response that can rapidly boost the number of T helper cells sensitive to a particular antigen. T_H17 cells were first described as having an origin distinct from T_H1 and T_H2 lineages, triggered by the cytokines IL-6 and TGF-β, but these did not seem to be autocrine messengers that could amplify the production of T_H17 cells.