International Immunology Advance Access originally published online on December 19, 2007
International Immunology 2008 20(2):215-222; doi:10.1093/intimm/dxm137
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Functional phenotype of macrophages depends on assay procedures
1 Department of Biomedical Engineering and Environmental Sciences, National Tsing Hua University, 101 Section 2, Kuang-Fu Road, Hsinchu 30013, Taiwan
2 Department of Radiation Oncology, Chang Gung Memorial Hospital, Tao-Yuan 30033, Taiwan
3 Department Radiation Oncology, David Geffen School for Medicine, University of California, Los Angeles, Los Angeles, CA, USA
Correspondence to: C.-S. Chiang; E-mail: cschiang{at}mx.nthu.edu.tw
Macrophages display different phenotypes that can switch in response to their micro-environment. In our earlier study (Chiang, C. S., Liu, W. C. and Jung, S. M., 2005. Compartmental responses after thoracic irradiation of mice: strain differences. Int. J. Radiat. Oncol. Biol. Phys. 62:862) on radiation-induced cytokine expression in lung lavage samples, there was a suggestion that the procedures used to harvest lung macrophages affected the profiles they expressed. To further explore this issue, we examined gene expression by cell populations, mainly macrophages, isolated by lavage from lung and peritoneal cavity following either in vivo or in vitro stimulation with LPS, IFN-
or irradiation. We found that expression of mRNA for tumor necrosis factor-alpha, IL-1
/β and IL-6 varied several fold depending on whether the assay was performed on cells immediately after isolation or after in vitro manipulation. The relative level of inducible nitric oxide synthase (iNOS) to arginase I (Arg I), which is frequently used as index of the M1 versus M2 functional macrophage phenotype, also varied. LPS stimulation in vivo was able to change the profile from Arg I expression to one where the iNOS pathway became dominant, but was unable to do this in vitro. This contrasts with the ability of IFN- to generate an iNOS-dominant pathway in vitro, but not in vivo. This study cautions that the expression of inflammatory cytokines and the iNOS to Arg I ratio, which is often used as an index of their functional capacity, varies with the experimental conditions.
Keywords: arginase, cytokines, nitric oxide synthase
Transmitting editor: A. Falus
Received 10 October 2007, accepted 25 November 2007.
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