Major histocompatibility complex antigens in the rat CNS following herpes simplex virus type 1 infection
Creators: name: Weinstein, Debra Lynn
Publisher: name: University of British Columbia
Year: 2010

description: The present study was designed to determine major histocompatibility complex (MHC) expression in the rat CNS following a viral infection. Male Wistar rats were anesthetized with ether and the right cornea was repeatedly scratched with a 23.5 gage needle. A 30 microliter drop of Herpes Simplex Virus Type 1 (HSV1) (PFU 33,000/mL) was placed on the scarified cornea. Animals were sacrificed 3, 6, 8, 10, 12, and 30 days following infection. Following decapitation, the brains were removed and placed in Zamboni fixative for immersion fixation. Monoclonal antibodies against rat MHC class I/class II antigens and HSV1 as well as polyclonal glial fibrillary acidic protein (GFAP) were used in both single and double staining procedures. Neurons staining positively for HSV1 were observed in the ipsilateral principal sensory nucleus of the fifth nerve. Fifth nerve axons were also positive. Additional infected areas included midline brainstem structures, hypothalamus, thalamus, cerebellum and diffuse cortical regions. Infection became increasingly pronounced through day 10. Two animals who recovered from the viral encephalitis were sacrificed on days 12 and 30; they demonstrated much less positive HSV1 staining. In the infected animals, serial sections revealed both class I and class II positive staining of non-neuronal cells in brain areas which were also positive for HSV1. Endothelial cells and cells with microglia-like morphology were positively stained for class I and expression increased through day 10. The class II positive cells had the morphology of leukocytes and microglia-like cells with increased expression occurring through days 8 and 10 throughout the brain. In serial sections, dense areas of class II positive microglia-like cells were located in the same areas as HSV1 positive clusters. MHC expression in the day 12 animal was quite pronounced with decreasing levels observed at 30 days. Tissue doubly stained for class II and GFAP demonstrated no overlap among positively stained cells suggesting that astrocytes were not expressing MHC glycoproteins. Astrocytes did, however, show morphological changes consistent with an acute CNS infection. Microglia are an endogenous component of the CNS which may be phagocytotic, but the full range of functions which microglia possess is still unclear. The results of the present study indicate that MHC expression occurs in the CNS as early as 6 days following viral infection with increased expression through day 10. Continued high levels of class II expression at 12 days, following substantial active virus clearing, strongly suggest ongoing immune system activity which appears to be present at least as long as 30 days post-infection. Peripherally, MHC expression is involved in the induction of an immune response, suggesting that the rat brain is capable of mounting an immune response to viral infection. Microglia expressing class II antigens may possess the ability to present antigen to T cells and thereby initiate an immune response within the CNS. The present study suggests that MHC antigens may play an active role in viral clearance from the CNS.