what is the function of t helper cells
T helper cell The T helper cells (Th cells) are a type of T cell that play an important role in the immune system, particularly in the adaptive immune system. They help the activity of other immune cells by releasing T cell cytokines. These cells help suppress or regulate immune responses. They are essential in B cell antibody class switching, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages.
Antigen Antigen presenting cells present antigens in the form of peptides on histocompatibility molecules. The T cell/T lymphocyte (a subtype of white blood cell), of the adaptive immune system, selectively recognize the antigens. Depending on the antigen and the type of the histocompatibility molecule, different types of T cells will be activated. For T-Cell Receptor (TCR) recognition, the peptide must be processed into small fragments inside the cell and presented by a major histocompatibility complex (MHC).[5] The antigen cannot elicit the immune response without the help of an immunologic adjuvant.[3] Similarly, the adjuvant component of vaccines plays an essential role in the activation of the innate immune system.[6][7]
T cell A T cell, or T lymphocyte, is a type of lymphocyte (a subtype of white blood cell) that plays a central role in cell-mediated immunity. T cells can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface. They are called T cells because they mature in the thymus from thymocytes[1] (although some also mature in the tonsils[2]). The several subsets of T cells each have a distinct function. The majority of human T cells rearrange their alpha and beta chains on the cell receptor and are termed alpha beta T cells (αβ T cells) and are part of the adaptive immune system. Specialized gamma delta T cells, (a small minority of T cells in the human body, more frequent in ruminants), have invariant T-cell receptors with limited diversity, that can effectively present antigens to other T cells[3] and are considered to be part of the innate immune system.
Cell-mediated immunity Historically, the immune system was separated into two branches: humoral immunity, for which the protective function of immunization could be found in the humor (cell-free bodily fluid or serum) and cellular immunity, for which the protective function of immunization was associated with cells. CD4 cells or helper T cells provide protection against different pathogens. Naive T cells, mature T cells that have yet to encounter an antigen, are converted into activated effector T cells after encountering antigen-presenting cells (APCs). These APCs, such as macrophages, dendritic cells, and B cells in some circumstances, load antigenic peptides onto the MHC of the cell, in turn presenting the peptide to receptors on T cells. The most important of these APCs are highly specialized dendritic cells; conceivably operating solely to ingest and present antigens. [1]