Immunohistochemical Characterization of Immune Cell Infiltration in Feline Glioma

The relationship between inflammatory cells and tumour biology has been defined in many human intracranial neoplasms, but it is relatively poorly characterized in veterinary medicine. The aim of this study was to define the immune cell infiltration in cases of feline glioma and its possible association with tumour morphology and type. A retrospective search identified 18 gliomas that met inclusion criteria. Tumours were subjected to immunohistochemistry (IHC) for CD3, CD20, Iba1, MAC387 and factor VIII-related antigen. For each antibody, the number of labelled cells was counted in 10 high-power (×400) fields and a cumulative score for each antibody was generated. Intratumoural and peritumoural CD3⁺ T lymphocytes were observed in all cases and occurred primarily within perivascular spaces and rarely around areas of necrosis or leptomeningeal spread. Perivascular CD20⁺ B lymphocytes were detected in 12/18 (67%) cases and occurred within and around tumours and near areas of leptomeningeal spread. MAC387 immunoreactivity highlighted intravascular monocytes in 9/18 (50%) cases, but failed to highlight tumour-associated macrophages. Intratumoural and peritumoural Iba1 immunoreactivity was observed in all cases, with increased overall intensity around areas of necrosis and leptomeningeal spread. Intratumoural and peritumoural factor VIII-related antigen immunoreactivity was also detected in all cases and was concentrated in areas of microvascular proliferation and necrosis. No significant associations were found between IHC scores for immune cells (i.e. lymphocytes and macrophages) and tumour morphology and type. Average factor VIII reactivity was higher in astrocytomas than oligodendrogliomas (P = 0.003).