FIG. 6.

Proposed infection route of CD8 lymphocytes circulating in vivo. We propose that circulating HIV-infected CD8 lymphocytes are generated through CD4-mediated infection of activated CD8 lymphocytes and that export of HIV-infected CD8 precursors from the thymus occurs rarely if at all. Since only a minority of memory CD8 lymphocytes express CD4, we propose that expression is transient and therefore show a CD4-negative “later ” memory CD8 lymphocyte. It is also possible that CD4 is expressed on a stable minority of memory CD8 lymphocytes. Dotted arrows represent possible lineage associations between cell types.