CD4 cells protect the body from infection by circulating in the blood to identify bacteria and viruses then produce antibodies to destroy them. CD4 cells also trigger the body to respond to infection by sending signals to other immune cells such as CD 8 cells that destroy bacterial and viral infections, according to About.com.
CD4 cells are a type of white blood cell made in the spleen, thymus gland and lymph nodes. CD4 is a molecular protein present on the surface of immune cells such as T-cells, monocytes, macrophages and dendritic cells. CD4 cells fight off bacteria and viruses before they weaken the body and cause illness. CD4 cells reduce viral and bacterial load, says About.com.
CD4 count is a measure of the number of CD4 cells per cubic millimeter in a sample of human blood. CD4 count ascertains the strength of a person's immune system. HIV binds to CD4 cells, altering their genetic coding, which limits their normal function and leaves the body vulnerable to opportunistic infections. CD4 count determines when an HIV-positive person starts antiretroviral therapy. Immune suppression resulting from a transplant also depletes CD4 cells. This weakens a body's immunity leaving the body susceptible to infection, as stated by WebMD.