Presence of tumor-associated macrophages (TAMs) in malignant

Presence of tumor-associated macrophages (TAMs) in malignant STI571 concentration tissue correlates frequently with worse disease

prognosis and higher propensity of metastasis [1-3]. Schematically, macrophages can be divided into two categories, representing two extreme phenotypes: inflammatory M1 and anti-inflammatory M2 macrophages. Other than the classical M1 macrophages endowed with antimicrobial and immune-stimulatory properties, the M2-skewed TAMs [1] dampen tumor-directed T-cell responses [4], stimulate angiogenesis [5-7], support tumor growth by cytokine supply [5, 8], and promote dissemination of malignant cells [1]. Despite our increasing knowledge of functional aspects of the tumor–TAM interplay, the ontogeny of tumor-resident macrophages is less well-understood. Macrophages in nonmalignant tissues can be of a dual, monocyte-dependent and/or monocyte-independent origin [9]. In the former case, blood monocytes extravasate to steady-state or inflamed tissues, where they terminally differentiate and replace aged or exploited macrophages.

This model proves its merit in case of acute inflammatory processes, in which a high demand for tissue macrophages exists due to their extensive turnover, but it fails to explain many phenomena observed under homeostasis or during chronic inflammation [10]. For instance, a plethora of highly RG7204 price specialized tissue-resident macrophages proliferate in situ under steady-state [11-15] and inflammatory conditions [16-19] and are able to self-maintain without significant input of marrow-derived precursors. TAMs settle inflammatory and dynamically expanding tumor environments with an elevated demand for macrophages supporting growth of the neoplasm. Circulating conventional monocytes (Gr-1+/ Ly6C+), either of BM or splenic origin, were shown to contribute markedly to the TAM pool [7,

20, 21]. On the other hand, recent reports on proliferating TAMs in human breast malignancies [3] indicate that TAMs may possess the capability to self-maintain independently of blood-borne precursors. An important aspect of TAM biology is how the malignant milieu influences differentiation of macrophages for tumor’s own sake. Ribociclib order In this respect, the potent hematopoietic cytokine CSF1 was proposed to be one of the main players [6, 8, 22]. The ubiquitously expressed CSF1 was proven to foster the development of various populations of tissue-resident macrophages and the complete maturation of blood monocytes [12]. In mammary cancer, CSF1 produced by tumor cells was shown to drive accumulation of TAMs that supply the neoplasm with the crucial growth factor EGF [8]. Studies on human breast carcinoma patients revealed a link between elevated expression of STAT1 and markers of macrophage infiltration with an impact on disease outcome [23].

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