Natural Infection with Rabies Virus: A Histopathological and Immunohistochemical Study of Human Brains

Abstract

Objectives: Despite all the efforts and increased knowledge of rabies, the exact mechanisms of infection and mortality from the rabies virus are not well understood. To understand the mechanisms underlying the pathogenicity of rabies virus infection, it is crucial to study the tissue that the rabies virus naturally infects in humans.

Methods: Cerebellum brain tissue from 9 human post mortem cases from Iran, who had been infected with rabies virus, were examined histopathologically and immunohistochemically to evaluate the innate immune responses against the rabies virus.

Results: Histopathological examination revealed inflammation of the infected cerebellum and immunohistochemical analyses showed an increased immunoreactivity of heat shock protein 70, interleukin-6, interleukin-1, tumor necrosis factor-alpha, caspase-3, caspase-9, toll-like receptor3 and toll-like receptor4 in the infected brain tissue.

Conclusion: These results indicated the involvement of innate immunity in rabies infected human brain tissue, which may aggravate the progression of this deadly disease.

Keywords: central nervous system; human; immunohistochemistry; pathology; rabies; tissue.

Figure 1

The aggregates of rabies virus nucleocapsid protein viewed as green fluorescence by the fluorescent antibody test.

Figure 2

Hematoxylin and eosin staining. (A) and (B) Astrocytic proliferation, astrocyte nuclei are somewhat enlarged and appear more numerous than expected (arrows) associated with astrocytic swelling (arrow head), magnification ×100. (C) Perineuronal satellite oligodendroglia (arrows) surround degenerate neurons with condensed chromatin and little cytoplasm, H&E staining, magnification ×200. (D),(E) and (F) Neuronal cell bodies are red, angular, and shrunken and their nuclei are contracted and dense (yellow arrow). The necrotic neuron cell body is surrounded by macrophages that will phagocytose the cell debris (arrow head). Perivascular cuffing (arrow) associated with neuronal degeneration (arrow head), H&E staining, magnification ×100. (G) and (H) Negri bodies, formed within neurons of the CNS have long been the hallmark of rabies infection (arrows), magnification ×200.

Figure 3

Immunohistochemical staining of cerebellum tissue sections. (A) Increased expression of apoptosis markers (caspase 3 and caspase 9) and inflammatory markers (IL-6, IL-1β, TNF-α, HSP70, TLR3, TLR4) in rabies groups compared to control groups are shown. Nuclei are stained with hematoxylin (blue), whereas apoptosis markers and inflammatory markers are stained in dark brown. (B) Bar charts showing the percentage of positive cells. Each value indicates the mean ± SEM. ** p < 0.01. *** p < 0.001.