α4-Integrin Antibody Treatment Blocks Monocyte/Macrophage Traffic to, Vascular Cell Adhesion Molecule-1 Expression in, and Pathology of the Dorsal Root Ganglia in an SIV Macaque Model of HIV-Peripheral Neuropathy

Abstract

Traffic of activated monocytes into the dorsal root ganglia (DRG) is critical for pathology in HIV peripheral neuropathy. We have shown that accumulation of recently recruited (bromodeoxyuridine(+) MAC387(+)) monocytes is associated with severe DRG pathology and loss of intraepidermal nerve fibers in SIV-infected macaques. Herein, we blocked leukocyte traffic by treating animals with natalizumab, which binds to α4-integrins. SIV-infected CD8-depleted macaques treated with natalizumab either early (the day of infection) or late (28 days after infection) were compared with untreated SIV-infected animals sacrificed at similar times. Histopathology showed diminished DRG pathology with natalizumab treatment, including decreased inflammation, neuronophagia, and Nageotte nodules. Natalizumab treatment resulted in a decrease in the number of bromodeoxyuridine(+) (early), MAC387(+) (late), CD68(+) (early and late), and SIVp28(+) (late) macrophages in DRG tissues. The number of CD3(+) T lymphocytes in DRGs was not affected by natalizumab treatment. Vascular cell adhesion molecule 1, an adhesion molecule that mediates leukocyte traffic, was diminished in DRGs of all natalizumab-treated animals. These data show that blocking monocyte, but not T lymphocyte, traffic to the DRG results in decreased inflammation and pathology, supporting a role for monocyte traffic and activation in HIV peripheral neuropathy.

Figure 1

Decreased dorsal root ganglia (DRG) pathology with natalizumab treatment. The terminology used during histological examination is defined as follows: satellitosis, increased numbers of cells around a neuronal cell body; Nageotte nodule, focal proliferations of satellite cells that partially to completely replace foci of neuronal cell loss; and neuronophagia, increased numbers of satellite cells infiltrating a neuronal cell body. Neuronophagia is a precursor lesion to the development of a Nageotte nodule. Cells were identified by morphology and the pattern of tissue reaction detailed above. Neurons were not counted, but loss was examined by the presence of Nageotte nodule and neuronophagia, which are satellite cells that replace foci of neuronal cell loss. A: A representative image of a DRG from an early untreated with a mild increase in satellite cells with a Nageotte nodule (arrow). B: A representative image of a DRG from an early natalizumab-treated animal with mild increase in satellite cells with no evidence of neuronophagia or Nageotte nodules. C: A representative image of a DRG from a late-untreated animal with multifocal foci of inflammation with neuronophagia (arrows). D: A representative image of a DRG from a late natalizumab-treated SIV-infected CD8-depleted rhesus macaque with moderate increase in satellite cells with rare neuronophagia (arrow). Hematoxylin and eosin was the stain. Original magnification, ×200 (A–D).

Figure 2

Natalizumab treatment results in a decrease in monocyte traffic, macrophage activation, SIV infection, but not numbers of CD3⁺ T cells in dorsal root ganglia (DRGs). In DRG tissues from early untreated, early natalizumab-treated, late untreated, and late natalizumab-treated SIV-infected CD8-depleted rhesus macaques, the absolute number of MAC387⁺ monocytes/mm² of DRG (A), bromodeoxyuridine (BrdU)⁺ cells/mm² of DRG (B), CD68⁺ macrophages/mm² of DRG (C), CD163⁺ macrophages/mm² of DRG (D), CD3⁺ T cells/mm² of DRG (E), and SIV p28⁺ cells/mm² of DRG (F) was quantitated. At least eight nonoverlapping fields at ×200 magnification were quantitated per DRG tissue. The absolute number of cells was calculated by dividing the number of positively stained cells (diaminobenzidine-positive brown cells) by the area of tissue examined (cells/mm²). t-Test was used to detect variation in cell numbers between untreated and natalizumab-treated rhesus macaques. Data were expressed as means ± SEM (A–F). ^∗P < 0.05, ^∗∗P < 0.01, and ^∗∗∗P < 0.001.

Figure 3

Natalizumab treatment reduces vascular cell adhesion molecular (VCAM)-1 expression on surface of blood vessels in dorsal root ganglia (DRG). Representative images of DRG tissues stained with anti–VCAM-1 from an early untreated (A), an early natalizumab-treated (B), late untreated (C), and late natalizumab-treated (D) SIV-infected CD8-depleted rhesus macaque. Arrows show VCAM-1⁺ blood vessels. E: VCAM-1 expression was quantitated in DRG tissues from early untreated, early natalizumab-treated, late untreated, and late natalizumab-treated SIV-infected CD8-depleted rhesus macaques. The percentages of VCAM-1⁺ area of total area of tissue were calculated. t-Test was used to detect variation in cell numbers between untreated and natalizumab-treated rhesus macaques. Data are given as means ± SEM (E). ^∗P < 0.05.