Helper T cells have a variety of roles within the immune system. They often influence an adaptive immune response against disease, but they can also generate nonbeneficial responses. Those responses can lead to disaster, such as the destruction of the host. The purpose of this article is to clarify the role of helper T cells in the adaptive immune response. Here are some examples of the different types of helper T cells.
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Th1 cells recognize viral peptides
Although IL-4-producing TH2 cells are essential for optimal humoral immune responses, their predominance during viral infection was unexpected. In addition to their role in promoting IgG2a class switching, TH1 cells also help activate cytotoxic T cells in peripheral lymphoid organs. They also secrete IFN-g, which enhances viral antigen presentation to cytotoxic T cells. In addition, TH1 cells directly kill effector lymphocytes by producing a Fas ligand.
The production of IL-12 by dendritic cells stimulates the development of TH1 cells. IL-12 also encourages the production of IL-8 by eosinophils and macrophages. Mice lacking IL-12 are more prone to bacterial infections. In addition, parasitic protozoa stimulates the production of cytokines and antibodies, which ultimately leads to the activation of eosinophils.
Th2 cells kill infected host cells
CD4+ T cells, or “T helper cells,” are important components of the adaptive immune response. They help B cells produce antibodies and secrete cytokines. After infection, memory T lymphocytes form. They can rapidly multiply into a large number of effector T cells. They may be CD4+ or CD8+. A cell known as T-bet is capable of activating phagocytes and macrophages.
The cellular and humoral components of the adaptive immune response are responsible for directing a targeted and effective response against a pathogen. Infections in humans result in a cellular immune response that includes neutralizing immunoglobulins (IgG), epithelial IgA, and other proteins. The cellular immune response is also triggered by opsonizing antibodies. Opposing to the Th2 cell response, T-lymphocytes also provide a role in directing macrophage recruitment and assisting in Ig production.
Th1 cells activate dendritic cells
Dendritic cells play a key role in the immune system. As professional antigen-presenting cells, they initiate both innate and adaptive immune responses. When activated by an outside stimulus, dendritic cells undergo genetic reprogramming and convert from neoplastic cells to effector cells of the TH1 T cell subset. This process is a positive feedback loop in the adaptive immune response, since TH1 cells activate dendritic cells and facilitate the development of antigen-specific T-cells.
These immune cells produce cytokines, depending on their type. They direct the immune response by directing it to a specific antigen or pathogen, and contribute to the regulation of immune cells in tissue. They are also known as memory T cells, because they can differentiate into effector cells when substantial numbers respond to the same antigen at the same time. Th cells are also known to cause inflammation.
Th2 cells activate macrophages
In the adaptive immune response, CD4+ T cells are essential to the host’s defense against various pathogens. These cells are further differentiated into four types: naive T cells (TH0), Th1 and Th2 cells. Th2 cells, in particular, play an essential role in the immune response against extracellular parasites and are responsible for the development of allergic inflammatory diseases.
Th2 cells stimulate a variety of host-specific antigens, including IL-4. They also secrete IL-13, IL-4, and IL-5. Th2 cells also recruit eosinophils through the production of IL-5 and IL-9. TH2 cells also regulate the development of fibrosis in the liver. Moreover, they induce fibrotic responses in the surrounding tissues of parasite eggs.
Th2 cells stimulate dendritic cell production
Innate lymphoid cells (ILCs) are key players in the Th2 adaptive immune response. These cells are derived from common lymphoid progenitors, and are categorized according to the cytokines they produce and the transcription factors that control their development. ILCs can promote early immune responses to infection. The following table summarizes the contributions of DC and APC subsets to the Th2 immune response.
In addition to stimulating DC production, Th2 cells also recruit specialized immune cells to attack specific targets. They are involved in tissue eosinophilia, mast cell hyperplasia, and airway hyperresponsiveness. In addition, Th2 cells are involved in the regulation of B cell class switching to IgE and in the production of antibodies. Exacerbative allergic reactions and asthma are associated with the overactivation of Th2 cells.
