The M1/M2 Test System for Determining Macrophage Phenotypes

Macrophages are highly plastic innate immune cells that integrate diverse microenvironmental cues to adopt pro-inflammatory (M1) or anti-inflammatory (M2) functional states, which critically influence the pathogenesis of infectious, autoimmune, inflammatory, and malignant diseases. This review provides an overview of current concepts of macrophage ontogeny, functional heterogeneity, and disease-associated phenotypes, with a specific focus on experimental approaches used as M1/M2 test systems for macrophage phenotyping. The scope of the review encompasses commonly used experimental models, induction protocols for M1- and M2-like polarization, and key readouts, including gene-expression signatures and metabolic parameters. Particular emphasis is placed on reporter-based platforms (luciferase, BRET, fluorescent nanoparticle probes), label-free biophysical methods such as electrical impedance monitoring and metabolic profiling, and their application to dynamic, real-time assessment of macrophage phenotype in the context of tumor microenvironments and chemotherapeutic exposure. The potential of integrating reporter systems with single-cell omics, spatial transcriptomics, and patient-derived ex vivo platforms is considered, with a view to transforming M1/M2 test systems into clinically oriented assays capable of tracking macrophage programs during therapy and supporting the development of macrophage-targeted diagnostics and treatments.