Astrocytic reaction in the canine granulomatous meningoencephalomyelitis

Reação astrocítica na meningoencefalomielite granulomatosa canina

Dog; granulomatous meningoencephalomyelitis

Cão; meningoencefalomielite granulomatosa

COMMUNICATION

[Comunicação]

Astrocytic reaction in the canine granulomatous meningoencephalomyelitis

[Reação astrocítica na meningoencefalomielite granulomatosa canina]

L.S. Jardim¹, J.P. Andrade-Neto², A.C. Alessi^1*

¹Departamento de Patologia Veterinária, Fac. de Ciências Agrárias e Veterinárias - Unesp

Via Paulo D. Castellane, s/n

14884-900 – Jaboticabal, SP

2Clínica Alto da Lapa - São Paulo, SP

Recebido para publicação, após modificações, em 10 de janeiro de 2001.

The granulomatous meningoencephalomyelitis (GME) affects dogs of all ages and breeds (Summers et al., 1995) and has been described in many countries (Braund et al., 1978; Vandevelde et al., 1981; Thomas & Eger, 1989; Kipar et al., 1998). The etiology of GME is undefined. Canine distemper virus was supposed to be involved (Vandevelde et al., 1978), but recent works suggest a T cell-mediated delayed-type hypersensitivity of an organ-specific autoimmune disease (Kipar et al., 1998; Pedersen, 1999).

Astrocytes are important cells involved in CNS homeostasis and in the process of antigen presentation. Interactions between astrocytes and hematogenous cells are considered by authors in many pathological situations (Montgomery, 1994; Aschner, 1998). The demonstration of reactive astrocytes by the immunohistochemical detection of glial fibrillary acidic protein (GFAP) was utilized to study the density and the morphology of astrocytes in different CNS diseases like compressive myelopathy in horses (Yovich et al., 1991), bovine rabies (Machado & Alessi, 1997) and equine leukoencephalomalacia (Lemos & Alessi, 1999). The scope of the present study was to investigate the distribution and morphology of GFAP-reactive astrocytes in the canine GME, as well as to evaluate the B and T cells populations utilizing immunohistochemistry.

Six dogs were acquired from the Veterinary Clinic Alto da Lapa - São Paulo, Brazil and submitted to necropsy at the Department of Veterinary Pathology of FCAV–UNESP. The brain was carefully removed, fixed in 10% phosphate buffered formalin, pH 7.2. Paraffin-embedded samples were processed for histopathological and immunohistochemical studies. Staining methods used include hematoxylin-eosin (HE), Gomori metanamine stain (GMS) and Ziehl-Neelsen (ZN). The immunohistochemistry PAP (peroxidase antiperoxidase) technique was employed using the primary antibody anti-GFAP¹, anti-IgG (g chain) and anti-IgM (g chain) canine (KPL) and anti-CD3 (DAKO). The percent of IgG, IgM and CD3 positive cells and the cell body and nuclei area of GFAP astrocytes were determined utilizing the Image-Pro Plus System (Media Cybernetics).

The dogs, three males and three females, with age ranging from 2 to 6 years, presented variable clinical neurologic signs including facial paralysis, circling, ataxia, convulsions, head-tilt, nystagmus, loss of reflexes and general paralysis. All the animals died spontaneously after a period of one to three months from the onset of the symptoms. During this time the dogs were treated with corticoids. Necropsy revealed few significant findings, but a unilateral increase in the volume of the brainstem was noticeable in two dogs. The histopathological findings were consistent with those described by Braund et al. (1978), Thomas & Eger (1989), Sorjonen (1990), Kipar et al. (1998) and Muñana & Luttgen (1998). Search for rabies and distemper virus inclusions, fungi or acid-fast bacilli resulted negative.

The immunohistochemistry anti-GFAP showed a strong astrocytic response around the inflammatory cell infiltration and the perivascular cuffs, with increase in the size of the cytoplasm and nucleus and increase in the thickness of their processes (Fig. 1 and 2). From the total number of cells, 37.9% ± 10.6 were reactive to anti-IgG, 23.5%± 6.9 were reactive to anti-IgM, and 12%± 4.1 reactive to anti-CD3 antibody.

Astrocytes showed strong hypertrophy when located near the lesions. The increase reaches a mean of 302.6% in the area of the cell body and 88.9% of the nuclear area when compared with normal astrocytes. The cytoplasmic processes were clearly more evident in these hypertrophied astrocytes. They were seen in the neuropil as fragments. The number of astrocytes in these areas was apparently higher than in the normal areas, but in consequence of the irregularity of the distribution a numeric determination was not plausible. The average of IgG positive cells was higher than IgM or CD3 positive cells. Kipar et al. (1998) showed a predominance of CD3 cells. In fact, the elevated number of immune cells is important aspect of the lesions.

Immunohistochemical staining for GFAP revealed enlarged and intense stained astrocytes around the lesions. The nuclei was also enlarged. The cytoplasmic processes in the neuropil were evident because of their thickness, on the contrary of the normal areas. Astrocytes morphology showed in this study could be suggestive for the chronic pattern of astrocytosis of the dog. These aspects are different from the swelling of astrocytes that occur as an initial alteration early after brain injury (Montgomery, 1994).

Astrocytosis occurs in many CNS disorders of animals (Yovich et al., 1991; Machado & Alessi, 1997; Lemos & Alessi, 1999) and is described in the GME for the first time in this study.

The proportion of reactive cells to anti-IgG and anti-IgM was high, in contrast with the percent of cells reactive to anti-CD3. These results are in accordance with Vandevelde et al. (1981), but, on the other hand, Kipar et al. (1998) verified a predominance of CD3 positive cells.

In conclusion, an expressive astrocytic reaction associate with the presence of a high proportion of immune cells observed in this study, points out to an effective participation of the immune system in the pathogenesis of GME and an important involvement of the astrocytes.

Keywords: Dog, granulomatous meningoencephalomyelitis

RESUMO

A meningoencefalomielite granulomatosa (MEG) ocorre em cães de todas as raças, em qualquer idade e já foi descrita em vários países. Sua etiologia não é definida, mas sugere-se que uma reação de hipersensibilidade retardada esteja envolvida. Nas lesões há ocorrência de profuso infiltrado de células B e T, além de macrófagos. No presente estudo verificou-se, com técnicas de imunoistoquímica, a distribuição e a morfologia de astrócitos imunorreativos à proteína glial fibrilar ácida no encéfalo de cães acometidos por MEG e também as proporções de células imunorreativas a IgG, IgM e CD3. Foram utilizados seis cães, três machos e três fêmeas, com idade entre dois e seis anos. Observou-se acentuada astrocitose principalmente ao redor das lesões, com aumento da área do corpo celular e da área nuclear em 302,6% e 88,9%, respectivamente. Os processos citoplasmáticos dos astrócitos tornaram-se mais evidentes, aparecendo, às vezes, como fragmentos no neurópilo. Do total de células inflamatórias infiltradas, 37,9% eram IgG positivas, 23,5% IgM positivas e 12% CD3 positivas. Conclui-se que na MEG ocorre uma expressiva astrocitose associada com a presença de alta proporção de células imunes.

Palavras-chave: Cão, meningoencefalomielite granulomatosa

ACKNOWLEDGEMENTS

The authors would like to thank Fapesp and CNPq for financial support; M.I.Y. Campos and F.A. Ardison for technical assistance.

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Publication Dates

• Publication in this collection
  05 June 2002
• Date of issue
  Apr 2001

History

• Received
  10 Jan 2001