The microglial/macrophagic response at the tumour–brain border of invasive meningiomas

Abstract

Little is known about the immune response of the brain to invasive meningiomas. The present study was based upon the hypothesis that the microglial/macrophagic response towards brain-invasive meningiomas is dependent on the intactness of the pial-glial basement membrane. We immunostained sections from 40 brain-invasive meningiomas that were graded according to World Health Organization (WHO) 2007 criteria. Thirty-three tumours were histologically WHO grade II (18, 'otherwise benign', and 15, 'otherwise atypical'), and seven, grade III. Microglial/macrophagic cells were labelled with antibodies directed against major histocompatibility complex class II, CD68, CD14 and CD163. Anti-collagen IV was used to visualize basement membranes. Twenty-five per cent (10/40) meningiomas (1/18 WHO grade II 'otherwise benign', 3/15 grade II 'otherwise atypical' and 6/7 WHO grade III) contained microglial/macrophagic cells at the tumour-brain border. The presence of these cells correlated with the absence of the pial-glial basement membrane (BM) and with WHO grade III. The monocytic response was of two kinds: one consisted of a dense layer of mononuclear cells at the tumour-brain border in nine cases, the other of an elevated number of microglial cells expressing CD14 or CD163 (two cases). The immune response at the tumour-brain interface correlates with the absence of the pial-glial BM and with malignancy grade. It remains to be established whether the mononuclear cells at the tumour-brain border are native microglia or blood-derived macrophages.