Difference Between CD4 Cells and CD8 Cells

柯y Difference – CD4 Cells vs CD8 Cells

In the context of细胞介导的免疫力,T cells, generally referred toT lymphocytes， 扮演一个重要角色。因为他们在胸腺from thymocytes, they are referred to as T cells. T cells have two main categories:T helper (Th) cells和cytotoxic T cells (Tc)。由于存在两种不同类型的glycoproteins, i.e., CD4 and CD8, on the cell surface of Th cells and Tc cells, they are referred to as CD4+ T cells and CD8+ T cells, respectively.CD4+ T细胞识别由主要组织相容性复合物（MHC）II类提出的抗原和activate in order to kill intracellular microorganisms by releasing cytokines. CD8+ T cells only recognize抗原presented by MHC Class I and destroy infecting tumor cells and viruses directly.This is the key difference between CD4 cells and CD8 cells.

内容

1.Overview and Key Difference
2.What are CD4 Cells
3.What are CD8 Cells
4.Similarities Between CD4 Cells and CD8 Cells
5.并排比较 - 表格的CD4细胞与CD8细胞
6。概括

What are CD4 Cells?

CD4 is considered as a glycoprotein which plays a major role in the immune system. CD4 lies on the surfaces of some immune cells likedendritic cells, T helper cells,巨噬细胞, andmonocytes。CD4蛋白通常由人类中称为CD4基因的基因编码。CD4具有短的细胞质尾巴，由特殊氨基酸sequence that helps to initiate and communicate with tyrosine kinase Lck. This Lck is needed to activate the molecular components of the signaling cascade of a T cell which is activated. CD4 belongs to the免疫球蛋白像其他细胞表面受体一样。它由四个免疫球蛋白结构域D组成₁到d₄。These domains are situated on the extracellular surface of the respective cells. D₁和d₃are similar to immunoglobulin variable (IgV) domains while D₂和d₄are similar to the immunoglobulin constant (IgC) domains. CD4 interacts with β₂-domain of major histocompatibility complex (MHC) class II molecules with the help of D₁领域。因此，这些CD4对仅由MHC II类呈现的抗原具有特异性。

CD4 is known as a co-receptor of the T cell receptor (TCR). This helps in the communication with the antigen- presenting cells. CD4 and the TCR complex each bind to specific regions of the antigen-presenting cells with the influence of the extracellular D₁领域。There are diseases which are caused due to defects of CD4. For example, inHIV感染，HIV-1病毒通过CD4进入宿主T细胞，表达CD4的T细胞的数量也经历了进行性还原性。

什么是CD8细胞？

CD8被认为是在免疫系统中起作用的跨膜糖蛋白。CD8也被称为T细胞受体（TCR）的共受体。与TCR相似，CD8专门与主要的组织相容性复合物（MHC）I类结合。CD8主要位于细胞毒性T细胞和皮质胸腺细胞，天然杀伤细胞和树突状细胞的表面上。就像CD4一样，CD8也属于免疫球蛋白超家族。为了促进该功能，CD8形成由CD8链对组成的二聚体。CD8的常见类型是CD8-α和CD8-β。它由免疫球蛋白变量（IGV）组成，例如通过茎和细胞内尾巴连接到膜的细胞外域。通常，IGV像CD8-α型的细胞外结构域与I类MHC分子合作。分子之间的这种亲和力使细胞毒性T细胞的T细胞受体在激活抗原特异性期间与靶细胞紧密结合。

CD4细胞和CD8细胞之间有什么相似之处？

• CD4 and CD8 are surface proteins which are found on the surface of their respective cells.

• Both CD4 and CD8 are generated in the thymus and express the T-cell receptor.
• Both of them are considered as glycoproteins and belong to the immunoglobulin superfamily.

• 在没有T细胞受体的情况下，两者都能够与MHC分子结合。CD4和CD8还能够通过不同的机制改善抗原诱导的IL-2产生。

CD4细胞和CD8细胞有什么区别？

CD4 Cells vs CD8 Cells
CD4称为T辅助细胞。	CD8称为细胞毒性T细胞。
抗原识别
CD4 cells recognize antigens presented by Major Histocompatibility Complex (MHC) Class II.	CD8细胞仅识别MHC类别I的抗原。
Mechanism of Action
CD4 cells are situated on the surfaces of some immune cells like dendritic cells, T helper cells, macrophages, and monocytes.	纤维素是具有线性β葡萄糖链的线性结构。
Mechanism of Action
在CD4中，应激活抗原呈递细胞，以通过释放细胞因子杀死细胞内微生物	在CD8中，感染病毒和肿瘤细胞直接破坏。
功能
CD4 cells are responsible for the antigen presentation to B cells.	CD8细胞是间接的phagocytosis。

概括– CD4 Cells vs CD8 Cells

T cells are important in细胞介导的免疫力。它们从胸腺细胞中成熟在胸腺中。由于存在T细胞受体，T细胞与其他淋巴细胞区分开。T细胞有两种类型：TH细胞和TC细胞。糖蛋白CD4和CD8分别存在于TH细胞和TC细胞上。CD4+ T细胞识别由主要的组织相容性复合物（MHC）II类带来的抗原并激活以通过释放细胞因子来杀死细胞内微生物。CD8+ T细胞仅识别MHC I类呈现的抗原，并直接破坏感染肿瘤细胞和病毒。这是CD4细胞和CD8细胞之间的差异。

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Reference:

1. “Adaptive immunity.” Khan Academy,Available here。Accessed 18 Sept. 2017.
2. “CD8 T Cells.” British Society for Immunology,Available here。Accessed 18 Sept. 2017.

Image Courtesy:

1. “Antigen presentation” By user:Sjef- 自我制作，指的是this image。(CC BY-SA 3.0)viaCommons Wikimedia