CD4 cells are a type of lymphocyte (white blood cell). They are an important part of the immune system. CD4 cells are sometimes called T-cells.
There are two main types of T-cells. T4 cells, also called CD4+, are “helper” cells. They lead the attack against infections. T8 cells, (CD8+), are “suppressor” cells that end the immune response. CD8+ cells can also be “killer” cells that kill cancer cells and cells infected with a virus.
The ratio of CD4 cells to CD8 cells is often reported. This is calculated by dividing the CD4 value by the CD8 value. In healthy people, this ratio is between 0.9 and 1.9, meaning that there are about 1-2 CD4 cells for every CD8 cell.
In people with HIV infection, this ratio drops dramatically, meaning that there are many times more CD8 cells than CD4 cells.
Because the CD4 counts are so variable, some health care providers prefer to look at the CD4 percentages. These percentages refer to total lymphocytes.
If your test reports CD4% = 34%, that means that 34% of your lymphocytes were CD4 cells.
This percentage is more stable than the number of CD4 cells. The normal range for adults is between 20% and 40%.
A CD4 percentage below 14% indicates serious immune damage and is similar to a CD4 count of 200 cells/mm3, and is an indication that it is time to start treatment.
Answered by: Svilen Konov
The CD8 protein comes secondary to the CD4 protein in the story of HIV infection, but CD8 and CD4 are quite closely related in that they are cell surface proteins found predominantly on T cells, and they both bind to HLA protein on other cells.
CD8 is ordinarily found on the surface of killer T cells (as opposed to CD4, ordinarily found on the surface of helper T cells). CD8 binds to HLA class I on some other cell – which, as the diagram below shows, allows the T cell receptor protein to dock to HLA-I and check the antigen (“Ag”) which HLA is presenting.
If the shape of the T cell receptor matches the antigen which is being presented, then a sequence of signals is triggered inside the T cell which causes it to kill the cell which it’s attached to (if it’s a killer T cell) or induce others to kill it (if it’s a helper T cell).
