Tumor Necrosis Factor– (TNF–) and Macrophages in the Brain of HSV–1 Infected BALB/c Mice.

Abstract

Abstract: : Purpose: Macrophages play a central role in antigen presentation and produce a variety of proinflammatory cytokines and chemokines. Following uniocular anterior chamber (AC) inoculation of HSV–1, virus spreads to the suprachiasmatic nuclei (SCN) and at day 5 p.i. TNF–α is detected in this area. The objective of these studies was to determine if macrophages are responsible for production of TNF–α in the SCN and the injected eye. Methods: On day 0, 9.3 x 10⁴ PFU of the KOS strain of HSV–1 was injected into the AC of euthymic BALB/c mice. To deplete macrophages, mice in Group 1 (experimental) were injected intravenously with 0.2 ml of dichloromethylene–biphosphate liposomes (Cl₂MBP, clodronate) on day –1 and 3. Mice in Group 2 (control) were injected intravenously with 0.2 ml of liposomes containing PBS on day –1 and 3. On day 0, 9.3 × 10⁴ PFU HSV–1 (KOS) in a volume of 2 µl was injected in the AC of each mouse. Mice from both groups were sacrificed at day 5 and day 7 p.i. and the eyes and brain were removed. Fluorescence immunohistochemistry was used to identify and determine the location of macrophages and TNF–α in the ipsilateral eye and SCN of HSV–1 infected mice. The titer of virus in the ipsilateral eye, the ipsilateral SCN, and the contralateral SCN was determined by plaque assay. Results: Double staining of the injected eye and SCN for macrophages and for TNF–α revealed that macrophages were the primary source of TNF–α in the injected eye and SCN. The titer of virus in the injected eye and ipsilateral was not significantly different between clodronate–treated and control mice. However, the titer of virus in the contralateral SCN was significantly increased in clodronate treated mice compared with controls (9.09 x 10³ PFU vs. 3.74 x 10² PFU, p<0.05). Conclusions: The results suggest that TNF–α, produced by macrophages that infiltrate the contralateral SCN following uniocular AC inoculation of HSV–1, plays a role in limiting virus spread from the SCN to the optic nerve and retina of the injected eye and in so doing prevents HSV–1 infection of the retina of the injected eye.

Keywords: herpes simplex virus • retinitis • neuroprotection