Immunohistochemical comparison of mononuclear cell populations in diseases of the canine central nervous system
The distemper subgroup had less numerous cellular infiltrates with lysozyme expression minimally predominating over anti-canine Ig expression, and CD3+ expression, which was minimal. The 2 dogs with toxoplasmosis and neosporosis had marked lymphocytic perivascular infiltrates that were predominantly B-cell origin; lysozyme staining was less common, but predominated in the neosporosis case. CD3 antigen positive T cells were rare in this subgroup. The 2 unclassified cases had variable outcomes, with lysozyme, CD3, and B cell staining occurring in equal numbers. The 3 spinal lymphoma cases were B-cell origin. These results support the potential use of immunochemical staining of T and B cell lymphocytes and monocyte/macrophages in CNS tissues to better correlate postmortem disease diagnosis by demonstrating that: 1) Subpopulations of mononuclear cells can be determined by assessing antigen expression and 2) Different populations of mononuclear cells are present in dogs with GME, CDV, Toxoplasma gondii and Neospora caninum.A total of 39 dogs with histopathologically confirmed central nervous system (CNS) mononuclear pleocytosis were characterized immunohistochemically using antibodies against CD3, lysozyme, canine immunoglobulin (IgG, IgM, IgA), canine distemper virus, Toxoplasma gondii, and Neospora caninum. Twenty-six dogs had lesions compatible with granulomatous meningoencephalomyelitis (GME), 6 with canine distemper, 1 with toxoplasmosis, 1 with neosporosis, 2 with CNS lesions of unknown cause, and 3 with spinal cord lymphoma. All dogs were evaluated immunohistochemically for distemper, toxoplasma and neospora antigens. The dogs ranged in age from 2 months to 14 years and the ratio of females to males was 2:1 with no breed predilection. CNS lesions consisted primarily of mononuclear perivascular and granulomatous parenchymal and meningeal infiltrates. In some cases, white and gray matter necrosis also were present. Macrophages and lymphocytes comprised the majority of the infiltrates; their numbers varied within and between the disease categories. Dogs with GME had primarily CD3 antigen positive T cells, as well as, lysozyme positive cells.