Effector sites (lamina propria) of the GI tract show the most pronounced CD4+ T cell depletion in acute and early HIV-1 infection. Immunohistochemical characterization of the effector and inductive sites in the rectal biopsies. Using a PC-based image analysis system (KS 4000; Kontron), a standard area was set by the image analyzer. For the lamina propria, a total of 10–15 consecutive nonoverlapping fields were analyzed for each staining. For the GALT, two to five representative areas were chosen. (A) At a magnification of 25, a Giemsa-stained section is shown depicting a lymphoid nodule (inductive site) where the germinal center (GC) and T cell zone (T) are indicated. The effector compartment represented by the lamina propria (LP) is seen in the lower part of the section. (B and C) The inductive sites are densely populated with CD4+ T cells (stained red) in both group 1 (B) and HIV-1–uninfected (C) subjects. A magnification of 100. (D and E) Effector sites in acute and early HIV-1 infection (D) show significant depletion of CD4+ T cells (stained red) compared with HIV-1–uninfected controls (E). A magnification of 100. (F) In the inductive and effector compartments, the mean of CD4+ and CD8+ T cells per unit area was determined and the CD4/CD8 ratio was calculated. A comparison of the mean CD4/CD8 ratio (represented on the y axis) between HIV-1–uninfected (gray bars) and group 1 subjects (white bars) is shown.