- Email: [email protected]
Herpes simplex virus-induced demyelination
Journal of the Neurological Sciences, 1983, 60: 247-252
247
Elsevier
HERPES SIMPLEX VIRUS-INDUCED DEMYELINATION Effects of Reinfection and Challenge with Neuroantigens
KRISTER KRISTENSSON, BO SVENNERHOLM and ERIK LYCKE
Department of Pathology (Division of Neuropathology), Huddinge Hospital, Karolinska Institute, Stockholm, and Department of Virology, Institute of Medical Microbiology, University of Gothenburg (Sweden) (Received 21 December, 1982) (Revised, received 1 February, 1983) (Accepted 3 February, 1983)
SUMMARY
Mice injected into the snout with the F-strain of herpes simplex virus (HSV) showed demyelination in the central part of the trigeminal root and brainstem. In this well characterized model the effect of reinfection with a virulent strain of HSV, and of immunization with UV-light-inactivated HSV and neuroantigens were examined. A marked enhancement of demyelination was found in mice immunized with spinal cord extracts in Freund's adjuvant prior to the HSV infection. Whether this effect is mediated by a general stimulation of inflammatory or immune competent cells or is dependent upon exposure to specific antigens is not known.
INTRODUCTION
In mice non-fatal infections with herpes simplex virus (HSV) may be associated with development of demyelinating lesions in the central nervous system (CNS) (Townsend and Baringer 1976, 1979; Kristensson and Wisniewski 1978; Kristensson et al. 1979, 1982; Townsend 1981a). In animals surviving the acute phase of infection there are areas remyelinated by oligodendroglial cells and by Schwann cells invading the CNS. Virological and immunobiological aspects of HSV-induced demyelination have been presented recently (Townsend 1981b; Lycke 1983). It has been reported (Hochberg et al. 1977) that rats surviving intracerebral inoculation with HSV-1 and an attack of experimental allergic encephalitis (EAE) develop symptoms and pathological changes of EAE when challenged with a second This study was supported by a grant from the Medical Research Council (project No. B83-12X-04480-09C). 0022-510X/83/$03.00 © 1983 Elsevier Science Publishers B.V.
248 inoculation with HSV. The second HSV-I injection seems, thus, to exacerbate the immunobiologically induced EAE. Since latent HSV infections of ganglia are often reactivated with recurrence of clinically manifest HSV infection the possible effects of recurrent HSV infection on myelin integrity are of interest. In the present study we have exposed mice to a second HSV inoculation, simulating a recurrent infection, and to sensitization with neuroantigens, and studied the effects on the demyelination in the mouse trigeminal system. With this well characterized model peripheral inoculation of virus in the snout produces demyelination in the transitional area of the trigeminal nerve root where the CNS and the peripheral nervous system meet. MATERIALS AND METHODS Groups of 12 four-week-old, male Swiss albino mice of a laboratory strain were anesthetized by ether and infected with 105 pfu of the F strain HSV type 1 on the right side of the snout by scraping with a fine needle. The F strain causes no overt symptoms of disease when peripherally inoculated but consistently induces demyelinating foci in the central part of the trigeminal root (Kristensson et al. 1979). To augment the immune response against HSV proteins one group of mice was challenged with a subcutaneous injection of inactivated HSV (UV-light) in complete Freund's adjuvant (DIFCO) 10 days after virus inoculation. The effect of reinfection was studied with the neurotropic strain KJ502 of HSV-1 inoculated in the same way and in the same part of the snout of mice previously exposed to the F strain. A lyophilized powder of mouse spinal cord was used for neuroantigens. Groups of mice were injected into the flanks intracutaneously with a mixture of 0.2 mg mouse spinal cord powder, 0.03 mg of M. tuberculosis hominis H37RA (DIFCO) in 0.15 ml phosphate-buffered saline and 0.15 ml Freund's incomplete adjuvant (DIFCO). The experiment is outlined in Table 1. For histology the mice were perfused through the heart with 5~o glutaraldehyde in phosphate buffer. The trigeminal nerve roots were dissected, dehydrated and embedded in Epon. From each root 8 longitudinal 1-/~m thick sections were cut at different levels and stained with toluidine blue. The morphological lesions observed were scored, 1-4, grading as 1. the occurrence of single demyelinated axons, 2. demyelination of less than one-third of the CNS part of the root, 3. demyelination affecting between one- and two-thirds and as 4. demyelination of more than two-thirds of the trigeminal nerve root. RESULTS Small loci of demyelination were seen in the central part of the trigeminal nerve root 24 days after the infection with the F strain. In all groups of virus-infected animals a moderate inflammatory cell infiltration was observed with lymphocytes, a few plasma cells and macrophages containing myelin debris. A single injection of spinal cord antigen caused no demyelination. In mice infected with virus no signs of demyelination were observed at 44 days post infection, indicating that remyeImation occurs.
249 TABLE 1 P E R I P H E R A L ( S N O U T ) I N O C U L A T I O N O F M I C E W I T H HSV A N D LESIONS O F D E M Y E L I N A T I O N IN T H E T R I G E M I N A L N E R V E E N T R Y Z O N E OF T H E CNS
Day 0
10
24
F F F SpC SpC NaC1 F F
NaC1 IF SpC F NaCI
0.7 1.0 1.1 1.7 0
30
44
KJ NaC1 KJ
0.9 0 0.6
(6) (6) (5) (7) (0) (4) (0) (3)
F = virus strain F, KJ = virus strain KJ 502, IF = UV light-inactivated virus, SpC = spinal cord antigen. The numbers indicate pathological mean score value of 12 animals. Within brackets: the number of mice with demyelination in each group.
As seen in Table 1 demyelination was demonstrable in mice at 24 days post infection. The lesions of demyelination became more extensive when mice, in addition to HSV-infection, received 10 days later a subcutaneous injection with inactivated virus or an intracutaneous incubation with neuroantigens. Pronounced enhancement of the demyelination was seen when the spinal cord antigen was given first and the HSV infection 10 days later as a snout inoculation (Fig. 1). The results also suggest that the virulent HSV strain (KJ 502) can reactivate demyelination in mice previously infected with the less neuropathogenic F-strain. DISCUSSION
The present study corroborates previous observations that HSV can cause demyelination and emphasizes that HSV under conditions which favour a non-lethal course of disease causes myelin changes instead of the severe necrotizing changes predominant in the acute fatal disease (Kristensson and Wisniewski 1978; Martin 1982). In the HSV mouse model demyelination appears within 1 week post infection. Both astrocytes and oligodendrocytes are infected. Astrocytes seem to be well provided with HSV receptors (Vahlne et al. 1978, 1980) and it has been suggested that astrocytes of the CNS part of the trigeminal root are responsible for the local spread of the virus when cells are undergoing lysis (Townsend 1981b). As oligodendrocytes become infected early post infection (Kristensson et al. 1978), it is reasonable to assume that the initial demyelination might reflect lytic HSV infection ofoligodendroglia, as suggested for the demyelination associated with, for example, mouse hepatitis virus (JHM) (Weiner 1973; Powell and Lampert 1975). Immuno-
250
Fig. 1. Central part of the trigeminal root showing extensive demyelination with naked axons am! myelin degradation products. Mouse, injectedwith spinal cord extract in Freund's adjuvant and infccled 10 days later into the snout with HS~¢,F-strain. × 360. suppression by means of cyclophosphamide (Townsend and Baringer 1979) and experiments with nude, athymic mice (Townsend 1981a) have indicated that myelin injuries in HSV-infected mice are probably also dependent upon immune reactions. It is assumed that inflammatory cells invading the virus-affected area release proteolytic enzymes contributing to tissue changes including demyelination (Cammer et al. 1978). However, if cyclophosphamide is administered before or simultaneously with HSV the immunosuppression leads to enhanced spread of virus and more widespread and severe demyelination presumably by infection of myelinating cells (Kristensson et al. 1982). It was intriguing to find that myelin damage from virus infection became more pronounced in a CNS sensitized by previous immunization with spinal cord antigens. These observations are in accord with the enhancement of myelin de, struction by pertussis antigens in animals sensitized with encephalitogenic antigens (Levine and Wenk 1966) and exacerbation of experimental allergic encephalitis (EAE) by HSV infection of the rat CNS sensitized by EAE antigen (Hochberg et al. 1977). Immune reactions provoked by infection or antigen administration seem particularly harmful in the sensitized CNS. Whether this effect is mediated by a general stimulation of inflammatory or immune competent cells or is dependent upon exposure of specific antigens is not known. We noticed no marked increase in reactivity when neuroantigens were administered to mice previously inoculated with HSV. In contrast, persistent measles virus CNS infection renders hamsters more sensitive to immunization with EAE antigen (Massanari et al. 1979). There
251 seems to be some antigenic relationship between measles virus and myelin basic proteins (Panitch et al. 1979). The present study emphasizes that reinfection with HSV, as well as primary infection, can induce CNS demyelination. Whether demyelination also results from reactivated recurrent infection is unknown. The process of demyelination is enhanced if the animal is sensitized to myelin antigens. It is not known if HSV infection of the CNS triggers immune reactions against myelin. However, inoculation of mice with a neurotropic strain of vaccinia virus elicits formation of antibodies to brain antigens including myelin and myelin basic protein (Steck et al. 1981) and we are now studying whether this type of mechanism also may apply to the HSV infection. REFERENCES Cammer, W., B. R. Bloom, W.T. Norton and S. Gordon (1978) Degradation of basic protein in myelin by neutral proteases secreted by stimulated macrophages - - A possible mechanism of inflammatory demyelination, Proc. Nat. Acad. Sci. (USA), 75: 1554-1558. Hochberg, F. H., J. R. Lehrich and B. G. W. Arnason (1977) Herpes simplex infection and experimental allergic encephalomyelitis An experimental model system f o r reactivation of EAE, Neurology (Minneap.), 27: 584-587. Kristensson, K. and H. M. Wisniewski (1978) Arrest of myelination and demyelination in rabbit retina induced by herpes simplex virus infection, Neuropath. Appl. Neurobiol., 4: 71-82. Kristensson, K., A. Vahlne, L.A. Persson and E. Lycke (1978) Neural spread of herpes simplex virus types 1 and 2 in mice after corneal or subcutaneous (footpad) inoculation, J. Neurol. Sci., 35: 331 340. Kristensson, K., B. Svennerholm, L.A. Persson, A. Vahlne and E. Lycke (1979) Latent herpes simplex virus trigeminal ganglionic infection in mice and demyelination in the central nervous system, J. Neurol. Sci., 43: 253-264. Kristensson, K., B. Svennerholm, A. Vahlne, E. Nilheden, L. Persson and E. Lycke (1982) Virus-induced demyelination in herpes simplex virus-infected mice, J. Neurol. Sci., 53:205-216. Levine, S. and E.J. Wenk (1966) Exacerbation and transformation of allergic encephalomyelitis by pertussis vaccine, Proc. Soc. Exp. Biol. Med., 122: 115-117. Lycke, E. (1983) Virus induced structural and functional changes in neural cells. In: A. Lajtha (Ed.), Handbook of Neurochemistry, Vol. 10, Plenum Press, New York. Martin, J.R. (1982) Spinal cord and optic nerve demyelination in experimental herpes simplex virus type 2 infection, J. Neuropath. Exp. Neurol., 41: 253-266. M assanari, R. M., P. Y. Paterson and H. L. Lipton (1979) Potentiation of experimental allergic encephalomyelitis in hamsters with persistent encephalitis due to measles virus, J. Infect. Dis., 139: 297-303. Panitch, H.S., P. Swoveland and K.P. Johnson (1979) Antibodies to measles react with myelinic basic protein, Neurology (Minneap.), 29: 548-549. Powell, H.C. and P.W. Lampert (1975) Oligodendrocytes and their myelin-plasma membrane connections in JHM mouse hepatitis encephalomyelitis, Lab. Invest., 33: 440-445. Steck, A.J., R. Tschannen and R. Schaefer (1981) Induction of antimyelin and antioligodendrocyte antibodies by vaccinia virus, J. Neuroimmunol., 1:117-124. Towsend, J. J. (1981a) The demyelinating effect of corneal HSV infections in normal and nude (athymic) mice, J. Neurol. Sei., 50: 435-441. Townsend, J.J. (1981b) The relationship of astrocytes and macrophages to CNS demyelination after experimental herpes simplex virus infection, J. Neuropath. Exp. Neurol., 40: 369-379. Townsend, J.J. and J. R. Baringer (1976) Comparative vulnerability to peripheral and central nervous tissue to herpes simplex virus, J. Neuropath. Exp. Neurol., 35:100 (Abstract). Townsend, J.J. and J.R. Baringer (1979) Morphology of central nervous system disease in immunosuppressed mice after peripheral herpes simplex virus inoculation - - Trigeminal root entry zone, Lab. Invest., 40:178 182. Vahlne, A., B. Nystr6m, M. Sandberg, A. Hamberger and E. Lycke (1978) Attachment of herpes simplex virus to neurons and glial cells, J. Gen. Virol., 40: 35%371.
252 Vahlne, A., B. Svennerholm, M. Sandberg, A. Hamberger and E. Lycke (1980) Differences in attachment between herpes simplex type I and type 2 viruses to neurons and glial cells, Infect. lmmunol., 28: 675-680. Weiner, L.P. (1973) Pathogenesis of demyelination induced by a mouse hepatitis virus (JHM virus), Arch. Neurol. (Chic.), 28: 298-303.
247
Elsevier
HERPES SIMPLEX VIRUS-INDUCED DEMYELINATION Effects of Reinfection and Challenge with Neuroantigens
KRISTER KRISTENSSON, BO SVENNERHOLM and ERIK LYCKE
Department of Pathology (Division of Neuropathology), Huddinge Hospital, Karolinska Institute, Stockholm, and Department of Virology, Institute of Medical Microbiology, University of Gothenburg (Sweden) (Received 21 December, 1982) (Revised, received 1 February, 1983) (Accepted 3 February, 1983)
SUMMARY
Mice injected into the snout with the F-strain of herpes simplex virus (HSV) showed demyelination in the central part of the trigeminal root and brainstem. In this well characterized model the effect of reinfection with a virulent strain of HSV, and of immunization with UV-light-inactivated HSV and neuroantigens were examined. A marked enhancement of demyelination was found in mice immunized with spinal cord extracts in Freund's adjuvant prior to the HSV infection. Whether this effect is mediated by a general stimulation of inflammatory or immune competent cells or is dependent upon exposure to specific antigens is not known.
INTRODUCTION
In mice non-fatal infections with herpes simplex virus (HSV) may be associated with development of demyelinating lesions in the central nervous system (CNS) (Townsend and Baringer 1976, 1979; Kristensson and Wisniewski 1978; Kristensson et al. 1979, 1982; Townsend 1981a). In animals surviving the acute phase of infection there are areas remyelinated by oligodendroglial cells and by Schwann cells invading the CNS. Virological and immunobiological aspects of HSV-induced demyelination have been presented recently (Townsend 1981b; Lycke 1983). It has been reported (Hochberg et al. 1977) that rats surviving intracerebral inoculation with HSV-1 and an attack of experimental allergic encephalitis (EAE) develop symptoms and pathological changes of EAE when challenged with a second This study was supported by a grant from the Medical Research Council (project No. B83-12X-04480-09C). 0022-510X/83/$03.00 © 1983 Elsevier Science Publishers B.V.
248 inoculation with HSV. The second HSV-I injection seems, thus, to exacerbate the immunobiologically induced EAE. Since latent HSV infections of ganglia are often reactivated with recurrence of clinically manifest HSV infection the possible effects of recurrent HSV infection on myelin integrity are of interest. In the present study we have exposed mice to a second HSV inoculation, simulating a recurrent infection, and to sensitization with neuroantigens, and studied the effects on the demyelination in the mouse trigeminal system. With this well characterized model peripheral inoculation of virus in the snout produces demyelination in the transitional area of the trigeminal nerve root where the CNS and the peripheral nervous system meet. MATERIALS AND METHODS Groups of 12 four-week-old, male Swiss albino mice of a laboratory strain were anesthetized by ether and infected with 105 pfu of the F strain HSV type 1 on the right side of the snout by scraping with a fine needle. The F strain causes no overt symptoms of disease when peripherally inoculated but consistently induces demyelinating foci in the central part of the trigeminal root (Kristensson et al. 1979). To augment the immune response against HSV proteins one group of mice was challenged with a subcutaneous injection of inactivated HSV (UV-light) in complete Freund's adjuvant (DIFCO) 10 days after virus inoculation. The effect of reinfection was studied with the neurotropic strain KJ502 of HSV-1 inoculated in the same way and in the same part of the snout of mice previously exposed to the F strain. A lyophilized powder of mouse spinal cord was used for neuroantigens. Groups of mice were injected into the flanks intracutaneously with a mixture of 0.2 mg mouse spinal cord powder, 0.03 mg of M. tuberculosis hominis H37RA (DIFCO) in 0.15 ml phosphate-buffered saline and 0.15 ml Freund's incomplete adjuvant (DIFCO). The experiment is outlined in Table 1. For histology the mice were perfused through the heart with 5~o glutaraldehyde in phosphate buffer. The trigeminal nerve roots were dissected, dehydrated and embedded in Epon. From each root 8 longitudinal 1-/~m thick sections were cut at different levels and stained with toluidine blue. The morphological lesions observed were scored, 1-4, grading as 1. the occurrence of single demyelinated axons, 2. demyelination of less than one-third of the CNS part of the root, 3. demyelination affecting between one- and two-thirds and as 4. demyelination of more than two-thirds of the trigeminal nerve root. RESULTS Small loci of demyelination were seen in the central part of the trigeminal nerve root 24 days after the infection with the F strain. In all groups of virus-infected animals a moderate inflammatory cell infiltration was observed with lymphocytes, a few plasma cells and macrophages containing myelin debris. A single injection of spinal cord antigen caused no demyelination. In mice infected with virus no signs of demyelination were observed at 44 days post infection, indicating that remyeImation occurs.
249 TABLE 1 P E R I P H E R A L ( S N O U T ) I N O C U L A T I O N O F M I C E W I T H HSV A N D LESIONS O F D E M Y E L I N A T I O N IN T H E T R I G E M I N A L N E R V E E N T R Y Z O N E OF T H E CNS
Day 0
10
24
F F F SpC SpC NaC1 F F
NaC1 IF SpC F NaCI
0.7 1.0 1.1 1.7 0
30
44
KJ NaC1 KJ
0.9 0 0.6
(6) (6) (5) (7) (0) (4) (0) (3)
F = virus strain F, KJ = virus strain KJ 502, IF = UV light-inactivated virus, SpC = spinal cord antigen. The numbers indicate pathological mean score value of 12 animals. Within brackets: the number of mice with demyelination in each group.
As seen in Table 1 demyelination was demonstrable in mice at 24 days post infection. The lesions of demyelination became more extensive when mice, in addition to HSV-infection, received 10 days later a subcutaneous injection with inactivated virus or an intracutaneous incubation with neuroantigens. Pronounced enhancement of the demyelination was seen when the spinal cord antigen was given first and the HSV infection 10 days later as a snout inoculation (Fig. 1). The results also suggest that the virulent HSV strain (KJ 502) can reactivate demyelination in mice previously infected with the less neuropathogenic F-strain. DISCUSSION
The present study corroborates previous observations that HSV can cause demyelination and emphasizes that HSV under conditions which favour a non-lethal course of disease causes myelin changes instead of the severe necrotizing changes predominant in the acute fatal disease (Kristensson and Wisniewski 1978; Martin 1982). In the HSV mouse model demyelination appears within 1 week post infection. Both astrocytes and oligodendrocytes are infected. Astrocytes seem to be well provided with HSV receptors (Vahlne et al. 1978, 1980) and it has been suggested that astrocytes of the CNS part of the trigeminal root are responsible for the local spread of the virus when cells are undergoing lysis (Townsend 1981b). As oligodendrocytes become infected early post infection (Kristensson et al. 1978), it is reasonable to assume that the initial demyelination might reflect lytic HSV infection ofoligodendroglia, as suggested for the demyelination associated with, for example, mouse hepatitis virus (JHM) (Weiner 1973; Powell and Lampert 1975). Immuno-
250
Fig. 1. Central part of the trigeminal root showing extensive demyelination with naked axons am! myelin degradation products. Mouse, injectedwith spinal cord extract in Freund's adjuvant and infccled 10 days later into the snout with HS~¢,F-strain. × 360. suppression by means of cyclophosphamide (Townsend and Baringer 1979) and experiments with nude, athymic mice (Townsend 1981a) have indicated that myelin injuries in HSV-infected mice are probably also dependent upon immune reactions. It is assumed that inflammatory cells invading the virus-affected area release proteolytic enzymes contributing to tissue changes including demyelination (Cammer et al. 1978). However, if cyclophosphamide is administered before or simultaneously with HSV the immunosuppression leads to enhanced spread of virus and more widespread and severe demyelination presumably by infection of myelinating cells (Kristensson et al. 1982). It was intriguing to find that myelin damage from virus infection became more pronounced in a CNS sensitized by previous immunization with spinal cord antigens. These observations are in accord with the enhancement of myelin de, struction by pertussis antigens in animals sensitized with encephalitogenic antigens (Levine and Wenk 1966) and exacerbation of experimental allergic encephalitis (EAE) by HSV infection of the rat CNS sensitized by EAE antigen (Hochberg et al. 1977). Immune reactions provoked by infection or antigen administration seem particularly harmful in the sensitized CNS. Whether this effect is mediated by a general stimulation of inflammatory or immune competent cells or is dependent upon exposure of specific antigens is not known. We noticed no marked increase in reactivity when neuroantigens were administered to mice previously inoculated with HSV. In contrast, persistent measles virus CNS infection renders hamsters more sensitive to immunization with EAE antigen (Massanari et al. 1979). There
251 seems to be some antigenic relationship between measles virus and myelin basic proteins (Panitch et al. 1979). The present study emphasizes that reinfection with HSV, as well as primary infection, can induce CNS demyelination. Whether demyelination also results from reactivated recurrent infection is unknown. The process of demyelination is enhanced if the animal is sensitized to myelin antigens. It is not known if HSV infection of the CNS triggers immune reactions against myelin. However, inoculation of mice with a neurotropic strain of vaccinia virus elicits formation of antibodies to brain antigens including myelin and myelin basic protein (Steck et al. 1981) and we are now studying whether this type of mechanism also may apply to the HSV infection. REFERENCES Cammer, W., B. R. Bloom, W.T. Norton and S. Gordon (1978) Degradation of basic protein in myelin by neutral proteases secreted by stimulated macrophages - - A possible mechanism of inflammatory demyelination, Proc. Nat. Acad. Sci. (USA), 75: 1554-1558. Hochberg, F. H., J. R. Lehrich and B. G. W. Arnason (1977) Herpes simplex infection and experimental allergic encephalomyelitis An experimental model system f o r reactivation of EAE, Neurology (Minneap.), 27: 584-587. Kristensson, K. and H. M. Wisniewski (1978) Arrest of myelination and demyelination in rabbit retina induced by herpes simplex virus infection, Neuropath. Appl. Neurobiol., 4: 71-82. Kristensson, K., A. Vahlne, L.A. Persson and E. Lycke (1978) Neural spread of herpes simplex virus types 1 and 2 in mice after corneal or subcutaneous (footpad) inoculation, J. Neurol. Sci., 35: 331 340. Kristensson, K., B. Svennerholm, L.A. Persson, A. Vahlne and E. Lycke (1979) Latent herpes simplex virus trigeminal ganglionic infection in mice and demyelination in the central nervous system, J. Neurol. Sci., 43: 253-264. Kristensson, K., B. Svennerholm, A. Vahlne, E. Nilheden, L. Persson and E. Lycke (1982) Virus-induced demyelination in herpes simplex virus-infected mice, J. Neurol. Sci., 53:205-216. Levine, S. and E.J. Wenk (1966) Exacerbation and transformation of allergic encephalomyelitis by pertussis vaccine, Proc. Soc. Exp. Biol. Med., 122: 115-117. Lycke, E. (1983) Virus induced structural and functional changes in neural cells. In: A. Lajtha (Ed.), Handbook of Neurochemistry, Vol. 10, Plenum Press, New York. Martin, J.R. (1982) Spinal cord and optic nerve demyelination in experimental herpes simplex virus type 2 infection, J. Neuropath. Exp. Neurol., 41: 253-266. M assanari, R. M., P. Y. Paterson and H. L. Lipton (1979) Potentiation of experimental allergic encephalomyelitis in hamsters with persistent encephalitis due to measles virus, J. Infect. Dis., 139: 297-303. Panitch, H.S., P. Swoveland and K.P. Johnson (1979) Antibodies to measles react with myelinic basic protein, Neurology (Minneap.), 29: 548-549. Powell, H.C. and P.W. Lampert (1975) Oligodendrocytes and their myelin-plasma membrane connections in JHM mouse hepatitis encephalomyelitis, Lab. Invest., 33: 440-445. Steck, A.J., R. Tschannen and R. Schaefer (1981) Induction of antimyelin and antioligodendrocyte antibodies by vaccinia virus, J. Neuroimmunol., 1:117-124. Towsend, J. J. (1981a) The demyelinating effect of corneal HSV infections in normal and nude (athymic) mice, J. Neurol. Sei., 50: 435-441. Townsend, J.J. (1981b) The relationship of astrocytes and macrophages to CNS demyelination after experimental herpes simplex virus infection, J. Neuropath. Exp. Neurol., 40: 369-379. Townsend, J.J. and J. R. Baringer (1976) Comparative vulnerability to peripheral and central nervous tissue to herpes simplex virus, J. Neuropath. Exp. Neurol., 35:100 (Abstract). Townsend, J.J. and J.R. Baringer (1979) Morphology of central nervous system disease in immunosuppressed mice after peripheral herpes simplex virus inoculation - - Trigeminal root entry zone, Lab. Invest., 40:178 182. Vahlne, A., B. Nystr6m, M. Sandberg, A. Hamberger and E. Lycke (1978) Attachment of herpes simplex virus to neurons and glial cells, J. Gen. Virol., 40: 35%371.
252 Vahlne, A., B. Svennerholm, M. Sandberg, A. Hamberger and E. Lycke (1980) Differences in attachment between herpes simplex type I and type 2 viruses to neurons and glial cells, Infect. lmmunol., 28: 675-680. Weiner, L.P. (1973) Pathogenesis of demyelination induced by a mouse hepatitis virus (JHM virus), Arch. Neurol. (Chic.), 28: 298-303.