helper T cell enhancement of adaptive immune response

Definition

Target type: biologicalprocess

Positive regulation of an adaptive immune response mediated via cytokine production by helper T cell. [GOC:add]

Helper T cells play a crucial role in amplifying and fine-tuning the adaptive immune response. They recognize antigen presented by antigen-presenting cells (APCs) via their T cell receptor (TCR) and become activated. Upon activation, helper T cells differentiate into various subsets, each with unique functions in orchestrating the adaptive immune response.

**Th1 cells** primarily promote cellular immunity. They secrete cytokines like interferon-gamma (IFN-γ) and tumor necrosis factor-alpha (TNF-α), which activate macrophages, enhance their ability to kill intracellular pathogens, and promote the differentiation of cytotoxic T lymphocytes (CTLs). CTLs, in turn, directly kill infected cells.

**Th2 cells** primarily promote humoral immunity. They secrete cytokines like interleukin-4 (IL-4) and interleukin-5 (IL-5), which stimulate B cell proliferation and differentiation into antibody-producing plasma cells. Antibodies neutralize pathogens, block their entry into cells, and activate complement pathways.

**Th17 cells** contribute to the defense against extracellular bacteria and fungi. They secrete cytokines like IL-17, which attracts neutrophils and other immune cells to the site of infection.

**T follicular helper (Tfh) cells** are specialized helper T cells that reside in lymphoid follicles. They provide help to B cells, promoting antibody class switching and affinity maturation.

**Helper T cell activation and differentiation:**

* **Antigen presentation:** APCs, like dendritic cells, macrophages, and B cells, engulf antigens and present them in the context of MHC molecules to helper T cells.
* **TCR engagement:** The TCR on helper T cells recognizes the antigen-MHC complex, initiating a signal transduction cascade.
* **Costimulation:** For full activation, helper T cells require a second signal, provided by costimulatory molecules like CD28.
* **Cytokine signaling:** The type of cytokines present in the microenvironment influences the differentiation of helper T cells into specific subsets.

**Helper T cell functions in adaptive immunity:**

* **Enhancement of antigen presentation:** Helper T cells can activate APCs, increasing their efficiency in presenting antigens to other immune cells.
* **Activation of other immune cells:** Helper T cells stimulate macrophages, CTLs, and B cells, amplifying the immune response.
* **Cytokine production:** Helper T cells produce a variety of cytokines that modulate the immune response, directing it towards specific targets.
* **Memory cell formation:** Helper T cells generate memory cells that persist for long periods, allowing for a faster and more effective response upon re-exposure to the same pathogen.

In summary, helper T cells play a crucial role in orchestrating and amplifying the adaptive immune response by activating and fine-tuning the functions of other immune cells, leading to the elimination of pathogens and the development of immunological memory.'
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