Proteomics Reveals a Role for Attachment in Monocyte Differentiation into Efficient Proinflammatory Macrophages

Monocytes are blood-borne cells of the innate immune system. They can be differentiated and activated into proinflammatory macrophages that might be employed in tumor immune therapy. Monocyte exposure to lipopolysaccharide (LPS) is a standard method to induce a proinflammatory macrophage state, with the resultant population comprising both adherent and nonadherent cells. In the current study, we aimed to identify the differences in proteomes of these monocyte subpopulations, which addresses a more general question about the role of attachment in monocyte differentiation. Label-free proteomics of a model of human monocytes (THP-1 cell line) revealed that the cells remaining in suspension upon LPS treatment were activated by cytokines and primed for rapid responsiveness to pathogens. In terms of proteome change, the adhesion process was orthogonal to activation. Adherent cells exhibited signs of differentiation and enhanced innate immune responsivity, being closer to macrophages. These findings indicate that adherent, LPS-treated cells would be more appropriate for use in tumor therapeutic applications.