We recognized two TAM populations present in these tumors, distinguishable by differential expression of CD11b and F4/80 markers. We explored a developmental interrelationship between monocytes and the two TAM populations and identified in situ proliferation as the essential mechanism responsible

for accumulation of the predominant TAM subset. Furthermore, our results underline the relevance of CSF1 for the life cycle of tumor-resident macrophages. Expression of Csf1 gene in tumor cells was controlled by STAT1 at the promoter level and this is postulated to account for the reduced macrophage infiltration in Stat1-null animals. Previously, we reported a link between high STAT1 expression and elevated levels of CD68 and CD163 transcripts as surrogate markers for TAM infiltration of breast carcinoma tissue [23]. We now included CSF1 in our investigations on https://www.selleckchem.com/products/AZD6244.html factors influencing the abundance of TAMs. STAT1 and CSF1 mRNA levels, adjusted for patient’s tumor stage and ER status, turned out to be positively Opaganib linked to the marker expression in four independent cohorts of breast carcinoma patients (Table 1). STAT1 was also found to correlate positively with CSF1 expression (Table 1). As reported, elevated STAT1 mRNA was associated with worse patient’s outcome in the Innsbruck cohort (overall survival hazard ratio, HROS = 1.37, 95% CI: 1.05–1.78, p = 0.021, Cox regression analysis). Interestingly, the effect of STAT1 on survival was strictly dependent

on CSF1 and CD68 since adjusting for these factors resulted in reduced HRs for STAT1 (HROS = 1.17, 95% CI: 0.87–1.57 after CSF1 adjustment; HROS = 0.97, 95% CI: 0.69–1.36 after CD68 adjustment). CSF1 and CD68 remained STAT1-independent prognostic factors (HROS = 1.51, 95% CI: 1.16–1.97, p = 0.0022 for CSF1 adjusted for STAT1; HROS = 1.51, 95% CI: 1.32–3.15, p = 0.0025 for CD68 adjusted for STAT1). Taken together, the prognostically relevant correlation between STAT1, CSF1, and macrophage marker expression brings forward a

hypothesis, whereby STAT1-regulated transcriptional programs are important for the accumulation of TAMs described to have negative impact on patient’s STK38 prognosis [2, 3]. We tested the above-presented hypothesis in spontaneous mammary neoplasms developed in MMTVneu mice. Two subsets of TAMs can be distinguished in these tumors: a major one, expressing CD11bloF4/80hi, and a minor one, marked as CD11bhiF4/80lo (Fig. 1A and B, and Supporting Information Fig. 1A). As described previously by our group, the abundance of TAMs was dependent on the Stat1-status of the animal [4]. Here, we can show that this effect is restricted to the CD11bloF4/80hi population, being significantly less abundant in Stat1-null tumors at all time points investigated (Fig. 1A, and Supporting Information Fig. 1B). Both TAM types expressed the monocyte/macrophage marker CD115 (CSF1 receptor [CSF1R]), which was slightly upregulated in Stat1-deficient macrophages (Fig.