Collagen deposition limits immune reconstitution in the gut

Abstract

Despite suppression of human immunodeficiency virus (HIV) replication by antiretroviral therapy, reconstitution of CD4+ cells is variable and incomplete, particularly in gut-associated lymphatic tissues (GALT). We have previously shown that immune activation and inflammation in HIV-infected and simian immunodeficiency virus-infected lymph nodes results in collagen deposition and disruption of the lymphatic tissue architecture, and this damage contributes to CD4+ cell depletion before treatment and affects the extent of immune reconstitution after treatment. In the present study, we compared collagen deposition and the extent of depletion and reconstitution of total CD4+ cells and subsets in peripheral blood, lymph nodes, and inductive and effector sites in GALT. We show that CD4+ cell depletion in GALT correlates with the rapidity and greater magnitude of collagen deposition in this compartment, compared with that in peripheral lymph nodes, and that although treatment does not restore CD4+ cells to effector sites, treatment in the early stages of infection can increase CD4+ central memory cells in Peyer patches.

Figure 1

Identification of central memory (CM) cells in Peyer patches of the terminal ileum. Triple-label immunofluorescence was used to identify and count CM CD4⁺ cells in the Peyer patches in tissue from the terminal ileum (CD4⁺, CD27⁺, and CD45RO⁺ cells). Tissue sections were stained with antibodies against CD4 (green in A), CD45R0 (blue in B), and CD27 (red in C). Images were collected at appropriate wavelengths for each fluorophore and combined in Photoshop (Adobe Systems) (D), where pixels were subtracted if they were not common to all 3 images. Pixels common to all 3 images were colored brown and CD4⁺ cells from A were recolored gray. A cell was counted as a CM cell if the brown pixels overlapped a gray cell and if >25% of the cell membrane was brown.

Figure 2

Compartmental analysis of the size of the CD4⁺ T cell population by HIV serostatus. Sections of lymph node and gut-associated lymphatic tissue from an HIV⁺ asnd HIV⁻ individual were stained with antibodies against CD4 and images were captured for quantitative image analysis. Cells stained brown are CD4⁺ cells. The images on the left are from a representative HIV⁻ individual, and those on the right are from a representative HIV⁺ person. The graphs on the right summarize the quantitative image analysis results for all patients. Top row, lymph node tissue; middle row, Peyer patches; bottom row, lamina propria.

Figure 3

Treatment-associated changes in CD4⁺ T cell populations (naive, central memory [CM], and effector memory [EM]) in the peripheral blood (A), lymph node tissue (B), Peyer patches (C), and lamina propria (D), according to CD4⁺ cell phenotype. Changes are shown for HIV⁻ persons and for HIV⁺ persons before and after 6 months of antiretroviral therapy (ART). There was a significant decrease in all phenotypes in each compartment when HIV⁻ and HIV⁺ individuals were compared, except for EM cells in peripheral blood and naive cells in Peyer patches. However, when day 0 and month 6 (after ART) were compared for HIV⁺ individuals, there was a significant increase of naive and CM cells in peripheral blood and of CM cells in Peyer patches. In lymph node tissue, there were small, statistically insignificant increases in naive and CM cells, and there was no change in EM cells in the lamina propria.

Figure 4

Treatment-associated changes in the central memory (CM) CD4⁺ T cell population in Peyer patches. CM CD4⁺ cells were measured for 1 HIV⁻ individual and for 6 HIV⁺ individuals before and after 6 months of antiretroviral therapy (ART) (2 in the acute-early stage of disease, 2 with chronic HIV infection, and 2 with AIDS). There was a significant increase in CM CD4⁺ cells if ART was started in the acute-early stage.

Figure 5

Collagen deposition in gut-associated lymphatic tissue (GALT). Representative sections from the Peyer patches and lamina propria of HIV⁻ persons and HIV⁺ persons with AIDS were stained with trichrome to identify collagen fibers. There was a significant increase in collagen deposition in the GALT of HIV⁺ individuals, compared with that of HIV⁻ individuals. The mean percentage of the GALT area (i.e., Peyer patches and lamina propria) that stained positive for collagen in HIV⁺ and HIV⁻ individuals was 15.5% and 4.4%, respectively (P=.002).

Figure 6

Comparison of collagen deposition in the T cell zone of lymph node tissue and Peyer patches in samples obtained from HIV⁺ persons in the acute-early stage of infection. Significantly greater amounts of collagen were deposited in the T cell zone of Peyer patches in gut-associated lymphatic tissue, compared to lymph node tissue, early after HIV acquisition (P = .03).

Figure 7

Comparison of the size of the overall (A) and naive (B) CD4⁺ T cell population and the amount of collagen in the T cell zone of Peyer patches. There was a significant and inverse relationship between the size of the overall CD4⁺ cell population in Peyer patches and the amount of collagen in the same tissue, and this relationship also held when we compared collagen deposition and naive CD4⁺ cell population in Peyer patches.