In the context of HAART, what does a CD4 count of less than 500 indicate?

A CD4 count of less than 500 indicates moderate immunodeficiency. In individuals with HIV, CD4 cells are crucial for the immune response, and monitoring their levels helps assess the health of the immune system. A CD4 count between 200 and 499 is classified as moderate immunodeficiency, which puts individuals at an increased risk for certain opportunistic infections, though they may not experience severe immunodeficiency. In this range, while the immune function is compromised, it is not classified as severe, which would be indicated by a CD4 count below 200. Therefore, a CD4 count below 500 reflects the status of the immune system where individuals require careful monitoring and may benefit from HAART (Highly Active Antiretroviral Therapy) to improve their immune function and reduce the risk of developing AIDS-related complications.

It's also important to note that at a CD4 count less than 500, individuals may start to be at a higher risk for some opportunistic infections, but this is particularly pronounced under a CD4 count of 350, illustrating why 'severe immunodeficiency' and 'stable immunity' would not apply.