CD4 is a protein found on the surface of immune cells, specifically CD4 T lymphocytes (CD4 cells or T helper cells), while CCR5 is a co-receptor that assists HIV in entering these cells.
CD4 Explained
- Definition: CD4 is a glycoprotein found on the surface of certain immune cells, most notably CD4+ T helper cells.
- Function: It acts as a primary receptor for HIV (Human Immunodeficiency Virus). CD4 cells play a crucial role in orchestrating the immune response by activating other immune cells, such as B cells and cytotoxic T cells, to fight infections.
- Importance: CD4 cell count is an important marker of immune function, especially in individuals with HIV. A low CD4 count indicates a weakened immune system, making individuals more susceptible to opportunistic infections.
- Role in HIV infection: HIV primarily targets CD4 cells, leading to their destruction. As the infection progresses, the CD4 count decreases, eventually leading to Acquired Immunodeficiency Syndrome (AIDS).
CCR5 Explained
- Definition: CCR5 (CC chemokine receptor type 5) is a protein found on the surface of some immune cells, including CD4 cells, macrophages, dendritic cells, and microglia.
- Function: CCR5 acts as a co-receptor for HIV. While HIV binds to the CD4 receptor, it also needs to bind to a co-receptor, such as CCR5, to successfully enter the cell.
- Genetic Variations: Some individuals have a genetic mutation called CCR5-delta32, which results in a non-functional CCR5 receptor. These individuals are highly resistant to HIV infection. If infected, these individuals tend to have a slower progression of HIV to AIDS.
- Therapeutic Target: CCR5 is a therapeutic target for HIV treatment. CCR5 antagonists (or CCR5 inhibitors) are medications that block CCR5, preventing HIV from entering CD4 cells. An example is Maraviroc.
CD4 and CCR5 Relationship in HIV Infection
In summary, CD4 is the primary receptor for HIV on T helper cells. CCR5 is a co-receptor that HIV uses in conjunction with CD4 to gain entry into the cell. Targeting either CD4 (though less common therapeutically) or CCR5 is a strategy for preventing HIV infection of immune cells. The presence of the CD4 receptor allows the virus to attach to the T helper cell, and the interaction with the CCR5 coreceptor enables the virus to fuse with the cell membrane and inject its genetic material, starting the infection process.
