Highly restricted spread of HIV-1 and multiply infected cells within splenic germinal centers

The tremendous dynamics of HIV infection finds expression in the tempo of s equence diversification. Genetic diversity calculations require the clearan ce of a majority of infected cells, the obvious predator being anti-HIV imm une responses. Indeed, infiltration of germinal centers (GCs) by HIV-specif ic CD8(+) cytotoxic T lymphocytes has been described. A corollary to this d escription would be limited diffusion of virus within lymphoid structures. HIV efficiently infects and replicates mainly in activated CD4(+) T lymphob lasts. These cells are found within GCs after their activation in the adjac ent periarteriolar lymphoid sheath (PALS). Here GCs and PALS have been diss ected from consecutive 10-mum sections through splenic tissue from three HI V-1-infected patients. Nested PCR amplification of the two first hypervaria ble regions of the env gene indicated that 38-78% of sections contained HIV -infected cells. Since there are several hundred CD4(+) T cells per CC sect ion, approximately 0.09-0.64% harbor proviral DNA. Such a low frequency not only suggests that virions on the follicular dendritic cell surfaces do no t readily infect adjacent T cells but also indicates highly restricted spre ad of HIV within GCs and the PALS. Sections were heavily infiltrated by CD8 (+) cells, which, together with a large body of extant data, suggests that the majority of infected cells are destroyed by HIV-specific cytotoxic T ly mphocytes before becoming productively infected. Finally, sequence analysis revealed that those HIV-positive cells were multiply infected, which helps explain widespread recombination despite a low overall frequency of infect ed cells.