Microglia and macrophages in human glioblastomas: A morphological and immunohistochemical study

Abstract

Glioblastomas (GBMs), a type of highly malignant brain tumour, contain various macrophages/microglia that are known as tumour-associated macrophages (TAMs). These TAMs have various roles in tumour biology. Histopathological aspects of TAMs and associations with tumour growth assessed by magnetic resonance imaging (MRI) are poorly described. In the present study, 16 patients that had sufficient tumour tissue and histological hallmarks were examined. The tumours were classified as either slow- (n=7) or fast-growing (n=9) based on the segmented tumour volumes from MRI scans taken at diagnosis and preoperatively. Using cluster of differentiation (CD)68 and ionized calcium-binding adaptor molecule 1 (Iba1) antibodies, the number, morphology, localization and distribution of TAMs in the GBM tissue were studied. TAMs were significantly more immunoreactive for anti-Iba1 (TAMs^Iba1) compared with anti-CD68 (TAMs^CD68; P<0.001). In central tumour areas and around vessels in the infiltration zone there were more TAMs^CD68 in slow-growing tumours (P=0.003 and P=0.025, respectively). Central tumour areas contained more TAMs compared with the infiltration zone (P=0.001 for TAMs^CD68 and P<0.001 for TAMs^Iba1). The majority of TAMs exhibited a ramified phenotype in the infiltration zone, whereas central TAMs were mostly amoeboid. TAMs were present in high numbers in most regions of the tumour, whereas there were few in necrotic areas. In conclusion, the present study demonstrated and confirmed that the high numbers of TAMs in GBMs assume a range of morphologies consistent with various activation states, and that slow-growing GBMs seem to contain a TAM-population different to their fast-growing counterparts.

Keywords: glioblastoma; immunohistochemistry; macrophages; microglia; tumour-associated macrophages.

Figure 1.

Central and peripheral regions of GBM. (A and B) Iba1 and (C and D) CD68 immunostainings illustrate the different phenotypes, and the numbers of TAMs in the (A and C) infiltration zones and (B and D) central areas. Central tumour areas contained mostly amoeboid TAMs; whereas, TAMs in the infiltration zones displayed a ramified phenotype. In addition, there were more TAMs in central tumour areas compared with infiltration zones (original magnification, ×200). GBM, glioblastoma; TAMs, tumour-associated macrophages.

Figure 2.

TAMs^Iba1 between vessels and necrotic areas. Large numbers of TAMs^Iba1 can be observed near vessels (asterisks) and extending into the adjacent necrotic area (arrows) that show few vessels, suggesting a migrant path originating from vessels and heading to necrosis (Fig. 3). The section is from a fast-growing tumour (original magnification, ×40). TAMs^Iba1, Iba1-immunoreactive tumour-associated macrophages.

Figure 3.

Increased number of TAMs^CD68 surrounding peripheral vessels in slow-growing tumours. In the infiltration zone of (A) fast-growing tumours, there are relatively few labelled TAMs^CD68 surrounding vessels compared with the numbers in (B) slow-growing tumours (original magnification, ×400). TAMs^CD68, CD68-immunoreactive tumour-associated macrophages.