“…It has been shown that GM-CSF and M-CSF, two commonly used factors in the experimental differentiation of macrophages from monocytes, can differentially regulate M1-M2 marker expression at baseline and also predispose macrophages to enhanced M1 and M2 responses, respectively, when further challenged by other stimuli ( Hamilton et al., 2014 ; Fleetwood et al., 2007 ). Different concentrations and durations of PMA (phorbol 12-myristate-13-acetate), which is widely used to condition the human monocytic THP-1 cells, also results in wide variations of downstream protein expression and ultimately nontrivial differences in their polarization responses ( Pinto et al., 2020 ). In addition, innate genetic differences between human and mouse macrophage cell lines ( Thomas and Mattila, 2014 ), between cell lines of human origin ( Mendoza-Coronel and Castanon-Arreola, 2016 ; Shiratori et al., 2017 ), and between mouse cell lines derived from different strains ( Santos et al., 2006 ) can all lead to differential macrophage phenotype outcomes (e.g., inconsistent marker expression patterns) when these cells are treated with the same stimulation.…”