Mesenchymal stem or stromal cells (MSCs) act on different components of the immune
response including macrophages (MPhis). Therefore this study has been committed to
explore how MSCs may modify the effect of MPhi polarization upon an inductive environment
using mouse bone marrow (BM)-derived "naive", unpolarized MPhis. Phagocytosis of various
MPhi subtypes was different since M1 and M2b showed poorer, while M2a higher rate
of phagocytosis. MSCs significantly promoted yeast ingestion by M1 and M2b and diminished
it by M2a cells. Under polarizing conditions, MSCs profoundly affected the TNFalpha
production of MPhi subtypes since M1 and M2b MPhis produced less and M2a produced
higher amount of TNFalpha while the amount of IL-10 was not affected. The most striking
effect of MSCs was registered on M2b cells since the inflammatory TNFalpha dominance
remarkably shifted to the immunosuppressive IL-10. Prepolarized M1 cells readily converted
to M2a and M2b states when polarizing conditions changed from M1 to M2a or M2b induction,
respectively. Repolarizing from M1 to M2a resulted in the decline of IL-10 and TNFalpha
and defined elevation of Ym1 similar to levels characteristic to M2a primarily polarized
from naive BM-MPhis. Similarly, polarization of M1 to M2b MPhis was successful showing
increase in IL-10 and reduction in TNFalpha levels characteristic to M2b cells. However,
when co-culturing with MSCs, M1-M2a or M1-M2b transition was not affected. Crosstalk
between MPhis and MSCs depended on PGE-2 since COX-2 inhibition reduced the effect
of MSCs to establish an IL-10-dominant cytokine production by MPhis.
