Remember that during HIV infection the primary event is the entry of the virus into CD4 + T lymphocytes and those cells that in addition to this molecule co-express chemokine receptors necessary for the internalization of viral particles. Then the main effect of the virus is to infect, multiply viral progeny and destroy mainly CD4 + T lymphocytes. But there are many additional important considerations: "A low CD4 / CD8 ratio in elderly HIV-uninfected adults is associated with increased morbidity and mortality." The subset of HIV-infected adults receiving effective antiretroviral therapy (ART) fails to normalize this ratio, even after they achieve Normal CD4 + T cell counts".

REFERENCE 2.

Dear Vielma , Thanks for your reply. I understand the importance of CD4:CD8 in HIV biology , pathogenesis and  treatment . My query was why not CD8:CD4 ? Because recently in a research work, I found correlation of  a biomarker with with CD4:CD8  ratio -.23 (r value), while if we take CD8:CD4 ratio , the correlation (r value) reached  0.5. In first case, it is showing negative correlation while in second case it is positive and higher correlation, though both were significant. From such situation this question came in to my mind. Therefore I was wondering why everybody is using CD4:CD8 ratio?!! Why not CD8 :CD4? It will be very helpful, if you kindly help me to get the answer. Thanks in advance.