Immunoperoxidase study of astrocytic reaction in Junín virus encephalomyelitis of mice

Intracerebral inoculation of strain XJ Clon 3 of Junín virus into 1-2-day-old mice resulted in the appearance of viral antigen, detectable by means of the peroxidase antiperoxidase (PAP) technique, within the cytoplasm of the neurons of the cerebral cortex, the basal nuclei, cerebellum, pons, medulla, spinal cord, and spinal ganglia; Junín antigen was likewise observed, although to a lesser extent, in the cytoplasm of astrocytes. The viral antigen was found in highest concentration at the cytoplasmic periphery, near the cell membrane, where complete virions are formed by budding. In some cells a "tigroid" distribution of the antigen was observed, suggestive of its production and concentration within the granular endoplasmic reticulum. In spite of the heavy infection of the neural structures, the neurons did not always show major alterations. By immunolabeling of the glial fibrillary acidic protein (GFAP) by the PAP method, a severe glial response could be seen in infected mice, featuring hyperplasia, hypertrophy, and shape distortion of the astrocytes. This easy labeling was not observed in normal mice of the same age, and suggests the accelerated maturation of the astrocytes and the increased GFAP synthesis by direct action of the virus upon such cells. In view of its specificity, use of the PAP technique for GFAP immunolabeling will most likely replace the traditional metal impregnation methods in the study of the astrocytes. Its utilization would be indicated whenever astroglial changes are suspected in any CNS pathologic condition.