Question

Please I want the similarities between CD4 and CD8..
(In response to pathogenic infection)
And you can explain that by the steps of infection

Answer 1

CD4 (cluster of differentiation 4) is a glycoprotein found on the surface of immune cells such as T helper cells, monocytes, macrophages and dendritic cells. Cells expressing CD4 are referred to as CD4 cells, T helper cells or T4 cells. CD8 (cluster of differentiation 8) is a transmembrane glycoprotein and is expressed on the surface of cytotoxic T cells, natural killer cells, corticl thymocytes and dendritic cells. One of the function of CD4 cells is to send signal to CD8 killer cell which then destroys the infectious particle. Both CD4 and CD8 serves as co receptor for T cell receptor (TCR). Both these glycoproteins assist TCR in communicating with antigen presenting cells. CD4 along with TCR binds to antigen-presenting MHC class II molecule whereas CD8 along with TCR binds to antigen-presenting MHC class I molecule. CD4 has 4 immunoglobulin domains (D1 to D4) which are expressed at the extracelluar surface of cells. D1 and D3 resembles immunoglobulin variable (IgV) domains and D2 and D4 resembles immunoglobulin constant (IgC) domains. For functioning CD8 forms dimer consisting of CD8 chains. The most common form of CD8 is composed of CD8-alpha and CD8-beta with immunoglobulin variable (IgV)-like extracellular domain. The extracellular D1 domain of CD4 binds to beta2 region of MHC class II while the extracellualr IgV-like domain of CD8-alpha interacts with alpha3 portion of MHC class I. Once the TCR binds to specific antigen the cytoplasmic tail of CD4 and CD8 interact with Lck (lymphocyte-specific protein tyrosine kinase). CD4 and CD8 along with TCR phosphorylates cytoplasmic CD3. These phosphorylation signals lead to the activation of transcription factors, including NF-κB, NFAT, AP-1, to promote T cell activation. The following figure depicts immune response of CD4 and CD8 expressing cells to pathogenic infection.