AIMS: Glioblastomas are highly aggressive and treatment resistant. Increasing 
evidence suggests that tumour-associated macrophages/microglia (TAMs) facilitate 
tumour progression by acquiring a M2-like phenotype. Our objective was to 
investigate the prognostic value of TAMs in gliomas using automated quantitative 
double immunofluorescence.
METHODS: Samples from 240 patients with primary glioma were stained with 
antibodies against ionized calcium-binding adaptor molecule-1 (IBA-1) and 
cluster of differentiation 204 (CD204) to detect TAMs and M2-like TAMs. The 
expression levels were quantified by software-based classifiers. The 
associations between TAMs, gemistocytic cells and glioblastoma subtype were 
examined with immuno- and haematoxylin-eosin stainings. Three tissue arrays 
containing glioblastoma specimens were included to study IBA-1/CD204 levels in 
central tumour and tumour periphery and to characterize CD204+ cells.
RESULTS: Our data revealed that the amount of especially CD204+ TAMs increases 
with malignancy grade. In grade III-IV, high CD204 expression was associated 
with shorter survival, while high IBA-1 intensity correlated with a longer 
survival. In grade IV, CD204 showed independent prognostic value when adjusting 
for clinical data and the methylation status of O6-methylguanine-DNA 
methyltransferase. Our findings were confirmed in two bioinformatics databases. 
TAMs were more abundant in central tumour tissue, mesenchymal glioblastomas and 
gliomas with many gemistocytic cells. CD204+ TAMs co-expressed proteins related 
to tumour aggressiveness including matrix metallopeptidase-14 and 
hypoxia-inducible factor-1α.
CONCLUSIONS: This is the first study to use automated quantitative 
immunofluorescence to determine the prognostic impact of TAMs. Our results 
suggest that M2-like TAMs hold an unfavourable prognostic value in high-grade 
gliomas and may contribute to a pro-tumourigenic microenvironment.