CD4 and CD4/CD8 ratio
Oct 11, 2002
Dear Mark, I have been recently diagnosed HIV+ (June 02) and have some questions regarding both the CD4/CD8 ratio and CD4 which do not seem to be spoken about as much as the CD4 absolute. My first question is what exactly are CD8 cells? What happens to them with HIV infection? My understanding is that they increase - is this correct and if so when in the course of infection (after how long)does this happen? Secondly what is the meaning/significance of the CD4/CD8 ratio? My doctor said that with HIV infection this declines/inverts - without meds what level does this ratio fall to and again when does this happen (immediately after infection or after a few months, a year??) Final question is re the CD4.How quickly does this fall on average per year without meds? What is the range? What weight do you place on the when someone has a >35 but a low CD4 because of a low WBC? Would you still start meds if the CD4 went below 350?
Thanks in advance for your response and for the great service you do - your work has certianly made the shock of HIV infection easier to deal with
Response from Dr. Holodniy
Lots of great questions. CD8 cells are the major defense in your immune system against HIV. For the most part they are cytotoxic t cells, meaning they kill HIV infected CD4 cells. They don't usually get infected with HIV. They do increase significantly after infection though. In the old days, we looked at the CD4/CD8 ratio as a measure of immune system suppression that was highly correlated with HIV disease progression. A normal ratio is about 1-1.5. In HIV infection, the CD4 cells become infected and decline, and the CD8 cells increase, hence the reduction in the ratio. In older natural history studies and in the absence of HIV meds, people tend to lose about 50 CD4 cells/year. The CD4 percentage is a more stable number over time compared to the absolute CD4 count, which can fluctuate for a variety of reasons. If someone had a CD4 percentage of 35% with a CD4 count < 350, I might be inclined to wait on starting treatment, if the viral load was relatively low (say <10,000), but I would be following the trend carefully.
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