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IFNs Reset the Differential Capacity of Human Monocyte Subsets to Produce IL-12 in Response to Microbial Stimulation
Alice Muglia Amancio1, Lara Mittereder1, Alexie Carletti1
1Laboratory of Parasitic Diseases, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD 20892.
Abstract:
Human primary monocytes are composed of a minor, more mature CD16+(CD14low/neg) population and a major CD16neg(CD14+) subset. The specific functions of CD16+ versus CD16neg monocytes in steady state or inflammation remain poorly understood. In previous work, we found that IL-12 is selectively produced by the CD16+ subset in response to the protozoan pathogen, Toxoplasma gondii In this study, we demonstrated that this differential responsiveness correlates with the presence of an IFN-induced transcriptional signature in CD16+ monocytes already at baseline. Consistent with this observation, we found that in vitro IFN-γ priming overcomes the defect in the IL-12 response of the CD16neg subset. In contrast, pretreatment with IFN-γ had only a minor effect on IL-12p40 secretion by the CD16+ population. Moreover, inhibition of the mTOR pathway also selectively increased the IL-12 response in CD16neg but not in CD16+ monocytes. We further demonstrate that in contrast to IFN-γ, IFN-α fails to promote IL-12 production by the CD16neg subset and blocks the effect of IFN-γ priming. Based on these observations, we propose that the acquisition of IL-12 responsiveness by peripheral blood monocyte subsets depends on extrinsic signals experienced during their developmental progression in vivo. This process can be overridden during inflammation by the opposing regulatory effects of type I and II IFN as well as the mTOR inhibition.
Insights
Human monocytes have two subsets: CD16+ and CD16-. The CD16+ subset produces IL-12, a response enhanced by IFN-gamma in CD16- monocytes, suggesting developmental regulation of immune responses.
Area of Science:
- Immunology
- Cell Biology
Background:
- Human primary monocytes consist of CD16+ and CD16- subsets with distinct functions.
- The roles of these monocyte subsets in immunity and inflammation are not fully understood.
- Previous studies identified IL-12 production by CD16+ monocytes in response to Toxoplasma gondii.
Purpose of the Study:
- To investigate the differential responsiveness of CD16+ and CD16- monocyte subsets to immune stimuli.
- To explore the factors influencing IL-12 production in these subsets.
- To understand the regulatory mechanisms governing monocyte subset function during inflammation.
Main Methods:
- Flow cytometry to identify monocyte subsets (CD14 and CD16 expression).
- In vitro stimulation assays using cytokines (IFN-γ, IFN-α) and pathway inhibitors (mTOR).
- Measurement of IL-12 production (IL-12p40 secretion) by monocyte subsets.
Main Results:
- CD16+ monocytes exhibit a baseline IFN-induced transcriptional signature.
- IFN-γ priming enhances IL-12 response in CD16- monocytes but has minimal effect on CD16+ monocytes.
- mTOR inhibition selectively increases IL-12 response in CD16- monocytes.
- IFN-α fails to induce IL-12 in CD16- monocytes and inhibits IFN-γ effects.
Conclusions:
- Monocyte subset responsiveness to IL-12 is influenced by developmental signals.
- Type I and II interferons (IFN) and mTOR pathway modulation can override baseline responsiveness during inflammation.
- Differential regulation of IL-12 production by monocyte subsets is critical in immune responses.
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