304 Heightened HIV-1 Replication in Lymphoid Follicles May Be Due to Immune Privilege J. Folkvord, E. Connick* Univ of Colorado Hlth Sci Ctr, Denver
Background: To evaluate the hypothesis that follicular regions of lymphoid tissue are immune privileged sites, HIV-producing cells and antiretroviral effector protein expression were quantified in follicular (F) and extra-follicular (EF) regions of inguinal lymph nodes (LN) from 15 untreated HIV-infected individuals.
Methods: Full cross-sections of snap frozen LN were stained for HIV RNA by in situ hybridization, and RANTES, IFN-gamma, IFN-alpha and perforin expression by immunohistochemistry. Sections were double-stained with anti-CD20, to define the F and EF regions, and frequencies of virus-expressing or protein-expressing cells were determined by quantitative image analysis. Tissues were double-stained for CD4 or CD8, and the proportion of F and EF regions that stained positively was determined. Statistical comparisons between F and EF regions were evaluated using Wilcoxon signed rank tests.
Results: Frequencies of virus-producing cells/mm2 tissue were consistently higher in F (median 1.2 cells/mm2 ) compared to EF regions (median 0.41 cells/mm2), with a median of 6-fold higher frequencies in F compared to EF tissue (p < 0.0001). The percentage of F that stained for CD4 was lower compared to EF regions, with a median F:EF ratio of 1:3.9 (range 1:0.71-1:54) (p = 0.0003). Assuming, as previously shown, that most productively infected cells are CD4+, these data suggest that a CD4+ T-cell is 31-fold (range 6- to 155-fold) more likely to be productively infected if it is located in F than in EF regions. RANTES-expressing cells were significantly less frequent in F regions (median 282 cells/mm2) compared to EF regions (median 1,025 cells/mm2) (p < 0.0001). IFN-gamma-expressing cells were less frequent in F regions (median 1.0 cells/mm2) compared to EF regions (median 2.7 cells/mm2) (p = 0.07). IFN-alpha expression was also less frequent in F regions (median 0.4 cells/mm2) compared to EF regions (median 3.1 cells/mm2) (p = 0.01). Perforin-expressing cells occurred at a similar frequency in both F (median 5.3 cells/mm2) and EF regions (median 4.1 cells/mm2) (p = 0.64). The proportion of the tissue area that stained for CD8 was lower in F regions compared to EF regions with a median ratio of 1: 3.7 (range 1:1.8-1:18) (p < 0.0001).
Conclusions: These data suggest that there is a relative paucity of most antiretroviral effector proteins and CD8+ T-cells in F compared to EF regions, which may contribute to the heightened virus replication at that site.
