Background:  a-defensins 1, 2, and 3 (AD), which are produced primarily in neutrophils, have been demonstrated to exert antiretroviral activity in vitro.  In HIV-1-infected individuals, AD have been reported to be released by CD8⁺ T-cells from long-term nonprogressors and to be associated with monocytes as well.  To assess their role in virologic control in vivo, we evaluated expression of AD in HIV⁺ lymphoid tissue and analyzed their relationship to virus replication.

Methods:  Lymph nodes from 15 HIV-1 seropositive and 6 HIV-1 seronegative individuals were evaluated by immunohistochemical (IHC) and immunofluorescent (IF) staining using antibodies to AD, CD68, CD8, CD20, and appropriate controls.  Virus-producing cells were identified by in situ hybridization (ISH) for HIV-1 RNA.

Results:  In HIV-1-infected subjects, the percentage of lymph node tissue area that stained positively by IHC for AD ranged from 0.9% to 8.6% (median, 4.6%), and was significantly higher than the percentage of AD expression in HIV-1 seronegative lymph node (median, 0.4%; range, 0.1 to 1.2%; p = 0.0007).  In lymph node from 5 HIV-1-infected individuals evaluated by IF, AD⁺ cells colocalized primarily with CD68⁺ cells (median, 87%; range, 81 to 95%), and less frequently with CD8⁺ cells (median, 4%; range, 4 to 8%) and CD20⁺ cells (median, 2%; range 1 to 3%).  AD expression was not significantly correlated with the number of virus-producing cells per mm² in lymph node tissue (r = 0.04; p = 0.89), plasma HIV-1 RNA concentration (r = -0.10; p = 0.71) or CD4⁺ T-cell count (r = 0.31; p = 0.26).  Percentage tissue expression of AD was significantly lower within lymphoid follicles (median, 2.5%) than in extra follicular lymph node regions (median, 4.9%; p = 0.01).  HIV-1-producing cells were significantly more frequent in lymphoid follicles (median, 1.19 cells/mm²; range 0.13 to 3.96) than in  extra follicular regions (median, 0.41 cells/mm²; range 0.01 to 1.61; p <0.0001).

Conclusions:  Expression of AD in lymph node is substantially elevated in HIV-1 infection.  AD in lymph node appear most frequently in association with monocytes or macrophages, but also occasionally with CD8⁺ cells and B-cells.  A relative paucity of AD expression in lymphoid follicles may contribute to heightened virus replication in those regions.

Keywords: alpha-defensins; lymphoid tissue; lymph node