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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.
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 .
On surfaces of helper T cells are CD4 receptors, as well as TCRs. When a naive helper T cell's CD4 molecule docks to an APC's MHC class II molecule, its TCR can meet and bind the epitope coupled within the MHC class II. This event primes the naive T cell.
The CD family of co-receptors are a well-studied group of extracellular receptors found in immunological cells. [4] The CD receptor family typically act as co-receptors, illustrated by the classic example of CD4 acting as a co-receptor to the T cell receptor (TCR) to bind major histocompatibility complex II (MHC-II). [5]
Antigen presentation stimulates immature T cells to become either mature "cytotoxic" CD8+ cells or mature "helper" CD4+ cells. An antigen-presenting cell (APC) or accessory cell is a cell that displays an antigen bound by major histocompatibility complex (MHC) proteins on its surface; this process is known as antigen presentation.
Cellular membranes separate these two cellular environments - intracellular and extracellular. Each T cell can only recognize tens to hundreds of copies of a unique sequence of a single peptide among thousands of other peptides presented on the same cell, because an MHC molecule in one cell can bind to quite a large range of peptides.
In COVID-19 B cell, natural killer cell, and total lymphocyte counts decline, but both CD4 + and CD8 + cells decline to a far greater extent. [12] Low CD4 + predicted greater likelihood of intensive care unit admission, and CD4 + cell count was the only parameter that predicted length of time for viral RNA clearance.
CD4-Ig works by mimicking the binding of CD4 to HIV, thereby preventing the virus from infecting T-helper cells. HIV infects T-helper cells by binding to the CD4 receptor and the co-receptor CCR5 or CXCR4. CD4-Ig binds to the viral envelope glycoprotein gp120, which is responsible for HIV binding to CD4. By binding to gp120, CD4-Ig prevents the ...