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The T helper cells (T h cells), also known as CD4 + cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines .
In molecular biology, CD4 (cluster of differentiation 4) is a glycoprotein that serves as a co-receptor for the T-cell receptor (TCR). CD4 is found on the surface of immune cells such as helper T cells , monocytes , macrophages , and dendritic cells .
T cells are grouped into a series of subsets based on their function. CD4 and CD8 T cells are selected in the thymus, but undergo further differentiation in the periphery to specialized cells which have different functions. T cell subsets were initially defined by function, but also have associated gene or protein expression patterns.
English: Depiction of the various key subsets of CD4-positive T cells with corresponding associated cytokines and transcription factors. Figure legend T cells leave the thymus in a naïve, antigen non-experiened state. After contact with antigen, T cells may take on one of numerous subsets.
T helper cell 22, also known as the Th22 cell, are a type of immune cell. Th22 are a derivative of naïve CD4+ T cells induced by the ligand activation of the transcription factor aryl hydrocarbon receptor (AhR), [ 1 ] which uses environmental, metabolic, microbial, and dietary cues to control complex transcriptional programmes. [ 2 ]
Some parts of this process may differ in CD4+ and CD8+ cells. For example, synapse formation is quick in CD8+ T cells, because for CD8+ T cells it is fundamental to eliminate the pathogen quickly. In CD4+ T cells, however, the whole process of the immunological synapse formation can take up to 6 hours. [13] [1]
Thymocytes are classified into a number of distinct maturational stages based on the expression of cell surface markers. The earliest thymocyte stage is the double negative stage (negative for both CD4 and CD8), which more recently has been better described as Lineage-negative, and which can be divided into four substages.
The threshold for positive and negative selection of developing T cells is regulated by the bound between the Lck and co-receptors. [10] There are two main pools of T cells which mediate adaptive immune responses: CD4+ T cells (or helper T cells), and CD8+ T-cells (or cytotoxic T cells) which are MHCII-and MHCI restricted respectively.