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Image of CD4 co-receptor binding to MHC (Major Histocompatibility Complex) non-polymorphic region. 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.
Exposed on the surface of the viral envelope, the glycoprotein gp120 binds to the CD4 receptor on any target cell that has such a receptor, particularly the helper T-cell. Strains of HIV-1 have been isolated that are able to enter host cells that are CD4 negative. This CD4-independence is associated with spontaneous mutation in the env gene.
Boehme et al. demonstrated this interesting dual outcome by blocking the binding of CD4 to MHC-II which prevented the programmed cell death reaction that active T-cells typically display. [6] The CD4 receptor is composed of four concatamerized Ig-like domains and is anchored to the cell membrane by a single transmembrane domain.
Since CD4 receptor binding is the most obvious step in HIV infection, gp120 was among the first targets of HIV vaccine research. Efforts to develop HIV vaccines targeting gp120, however, have been hampered by the chemical and structural properties of gp120, which make it difficult for antibodies to bind to it. gp120 can also easily be shed from the surface of the virus and captured by T cells ...
CD4 immunoadhesin was first developed in the mid-1990s as a potential therapeutic agent and treatment for HIV/AIDS. The protein is a fusion of the extracellular domain of the CD4 receptor and the Fc domain of human immunoglobulin G (IgG), the most abundant antibody isotype in the human body. [1]
The antigen-presenting cells (APC) expose on their surface a fraction of the antigen that is recognized either from CD8+ T cells or CD4+ T cells. This binding leads to the activation of TCR signaling cascade in which the immunoreceptor tyrosine-based activation motifs (ITAM) located in the CD3-zeta chains (ζ-chains) of the TCR complex, are ...
HLA-A projected away from the cell surface and presenting a peptide sequence. The peptide-MHC complex presents a surface that looks like an altered self to the TCR. [11] The surface consisting of two α helices from the MHC and a bound peptide sequence is projected away from the host cell to the T cells, whose TCRs are projected away from the T cells towards the host cells.
Gp120 binds to a CD4 and a co-receptor (CCR5 or CXCR4), found on susceptible cells such as Helper T cells and macrophages. [5] As a result, a cascade of conformational changes occurs in the gp120 and gp41 proteins. These conformational changes start with gp120 that rearranges to expose the binding sites for the coreceptors mentioned above.