Background:
Macrophages are immune cells known for the detection and destruction of
bacteria
and viruses. In addition, macrophages are vital for a more generalised
inflammatory response, providing cell-cell contacts and producing a
cocktail of cytokines that stimulate a variety of other
immunopathology's;including wound healing. Importantly, macrophages
exhibit plasticity in their specific phenotypes, able to transiently
convert between pro or anti-inflammatory subsets of cells along a
continuum. For example, the pro-inflammatory M1 subset are heavily
involved in immune modulation and the anti-inflammatory M2c subset is
central to the erythroblastic island in the bone marrow.
Aims:
The aim of our work was to further understand and characterise human macrophages and their polarity using a well characterised
in vitro
culture model. A multipronged approach of mass spectrometry, flow
cytometry and a previously described2 imaging pipeline was utilised to
interrogate the cell surface expression and behaviour of cultured cells.
Methods:
We compared three populations against our control
unstimulated macrophage (M.) population, including the classically
activated "inflammatory" M1 stimulated with
interferon-g (IFNg) against the non-classically activated M2a macrophage subset stimulated with interleukin-4 (
IL-4)
and finally M2c macrophages stimulated with dexamethasone. The
glucocorticoid dexamethasone was also applied as a treatment of the
inflammatory M1 subset to better understand the specific effects of this
steroid on macrophage polarisation to mimic anti-inflammatory steroid
treatment for diseases such as
COVID19.
Results:
In doing this we demonstrate an increase in CD163 and CD206, markers
synonymous with anti-inflammatory M2 macrophages when compared with
untreated M1 macrophages. We detected specific alterations in cell
surface markers and behaviour between the subsets of in vitroproduced
macrophages associated with the known phenotypes.
Summary/Conclusion:
This provides a detailed dissection of the macrophage polarity
continuum that is relevant to the macrophage field as a whole and to the
current situation with
COVID-19.
This ex vivo method of recapitulating an aspect of the inflammatory
response to disease has the prospect to be a test bed for future drugs
and therapeutics.