ORIGINAL ARTICLE Electrostatic Surface Potential of Macrophages Correlates with Their Functional Phenotype Papiya Chakraborty, 1 Pankaj Dipankar, 1 Shiba Prasad Dash, 1 Priya, 1 Shreya Srivastava, 1 Rajat Dhyani, 1 Naveen Kumar Navani, 1 Deepak Sharma, 1 and Pranita P. Sarangi 1,2 Abstract— Macrophages exist in various functional phenotypes, which could be identi- fied by specific surface molecules. Previous studies have shown that modulation of surface charges could alter the phagocytic function of macrophages. In this study, we show that ac- tivation of both human peripheral blood monocyte and THP-1-derived macrophages with lipopolysaccharide (LPS) or IL-1β resulted in a significant decrease in the zeta potential compared to freshly isolated monocytes and unstimulated macrophages. Interestingly, inter- action with bacteria significantly increased the zeta potential of such cells irrespective of activation conditions. Similarly, IFNγ-treated pro-inflammatory macrophages showed lesser negative zeta potential compared to untreated control. A moderate reduction was also seen in IL-4-treated anti-inflammatory subtype. Additionally, in an LPS-induced systemic inflam- mation model, bone marrow cells isolated after 2 h of LPS injection showed significant reduction in zeta potential compared to naïve cells. Furthermore, electrostatic potential measurement of surface proteins associated with pro-inflammatory and anti-inflammatory macrophages, using in silico modeling under physiological and protonation conditions, showed that the average electrostatic potential of pro-inflammatory type surface proteins was less negative than anti-inflammatory subtype. These data suggest that the expression of different protein molecules on macrophages under different environments may contribute to the zeta potential and that this quick and low-cost technique could be used in monitoring macrophage functional phenotypes. KEY WORDS: macrophage; cytokine; inflammation; zeta potential; charge on surface proteins. INTRODUCTION Macrophages are the key cell types of the innate immune system, which plays an important role in phago- cytosis, antigen presentation, and in mediating pro- and anti-inflammatory responses [1]. Precursor cells of macro- phage originate from the bone marrow and enter into the circulation as monocytes. Under physiological and inflam- matory conditions, the presence of different environmental stimuli such as cytokines and growth factors in the tissues Papiya Chakraborty and Pankaj Dipankar contributed equally to this work. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10753-019-01146-3) contains supplementary material, which is available to authorized users. 1 Department of Biotechnology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India 2 To whom correspondence should be addressed at Department of Bio- technology, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand, India. E-mail: psarafbt@iitr.ac.in 0360-3997/19/0000-0001/0 # 2019 Springer Science+Business Media, LLC, part of Springer Nature Inflammation ( # 2019) DOI: 10.1007/s10753-019-01146-3