Background:  a-Defensins 1, 2, and 3 exhibit antiretroviral activity in vitro, but their role in controlling HIV-1 replication in vivo and the cells that produce them are controversial. Previously we reported high levels of α-defensins in HIV-1-infected individuals’ lymphoid tissues, the major site of HIV-1 replication. In the present study we sought to determine the identity of the cells that produce a-defensins.

Methods:  a-Defensin expression was evaluated by immunostaining frozen inguinal lymph node sections from 19 HIV-1-infected individuals who were not receiving ART and 8 individuals at low risk or seronegative for HIV-1 who were undergoing surgery in the groin. Percentages of tissue sections that stained positively for a-defensins or CD15 (granulocyte marker) were quantified using image analysis. Disaggregated lymph node cells were double-stained with immunofluorescent antibodies for a-defensins and CD15 to evaluate whether there was co-localization. Nonparametric statistical tests were used to evaluate the data.

Results:  Percentages of tissue sections that stained positively for α-defensins were similar in HIV-seropositive (median, 7.6%; range 1.6 to 23.0) and seronegative (median, 5.5%; range 1.0 to 12.9) individuals. Several seronegative subjects had enlarged nodes, as well as underlying proinflammatory conditions, e.g., thrombophlebitis. Lymph node weight in seronegatives (but not seropositives) correlated with α-defensin expression (Spearman’s ρ = 0.8333; p = 0.015). Plasma HIV-1 RNA concentration was not significantly correlated with α-defensin expression. Percentages of tissue area that stained positively for CD15 were similar in HIV-seropositive (median, 5.9%; range, 2.3 to 25.4) and seronegative subjects (median, 3.9; range, 0.2 to 15.0). CD15 and a-defensin staining were highly correlated (Spearman’s ρ = 0.6216, p = 0.0005). Patterns of staining for CD15 and a-defensins were nearly identical in adjacent tissue sections of individual subjects. In disaggregated lymph node cells from 4 subjects, a median of 100% (range, 95 to 100%) of a-defensin-expressing cells also expressed CD15.

Conclusions:  a-Defensins are up-regulated in reactive lymph nodes, including those in HIV-1 infection, and are expressed primarily by granulocytes. The role of this innate immune response in controlling HIV-1 replication in vivo merits further investigation.