Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. An accumulation of fat, followed by inflammation, is the major cause of NAFLD progression. During inflammation, macrophages are the most abundant immune cells recruited to the site of injury. Macrophages are classified into “proinflammatory” M1 macrophages, and “anti-inflammatory” M2 macrophages. In NAFLD, M1 macrophages are the most prominent macrophages that lead to an excessive inflammatory response. Previously, we found that baicalin could polarize macrophages into anti-inflammatory M2c subtype macrophages with an increased level of MERTK expression. Several studies have also shown a strong correlation between MERTK expression and cholesterol efflux, efferocytosis, as well as phagocytosis capability. Therefore, in this study, we aim to elucidate the potential and efficacy of mononuclear-cell (MNC)-derived MERTK^+/hi M2c macrophages induced by baicalin as a cell-based therapy for NAFLD treatment. In our results, we have demonstrated that a MERTK^+/hi M2c macrophage injection to NAFLD mice contributes to an increased level of serum HDL secretion in the liver, a decline in the circulating CD4⁺CD25⁻ and CD8⁺CD25⁻ T cells and lowers the total NAFLD pathological score by lessening the inflammation, necrosis, and fibrosis. In the liver, profibrotic COL1A1 and FN, proinflammation TNFα, as well as the regulator of lipid metabolism PPARɣ expression, were also downregulated after injection. In parallel, the transcriptomic profiles of the injected MERTK^+/hi M2c macrophages showed that the various genes directly or indirectly involved in NAFLD progression (e.g., SERPINE1, FADS2) were also suppressed. Downregulation of cytokines and inflammation-associated genes, such as CCR5, may promote a pro-resolving milieu in the NAFLD liver. Altogether, cell-based therapy using MERTK^+/hi M2c macrophages is promising, as it ameliorates NAFLD in mice.

Macrophage colony-stimulating factor (M-CSF or CSF-1) is known to have a broad range of actions on myeloid cells maturation, including the regulation of macrophage differentiation, proliferation and survival. Macrophages generated by M-CSF stimulus have been proposed to be alternatively activated or M2 phenotype. M-CSF is commonly overexpressed by tumors and is also known to enhance tumor growth and aggressiveness via stimulating pro-tumor activities of tumor-associated macrophages (TAMs). Currently, inhibition of CSF-1/CSF-1R interaction by therapeutic antibody to deplete TAMs and their pro-tumor functions is becoming a prevalent strategy in cancer therapy. However, its antitumor activity shows a limited single-agent effect. Therefore, macrophages in response to M-CSF interruption are pending for further investigation. To achieve this study, bone marrow derived macrophages were generated in vitro by M-CSF stimulation for 7 days and then continuously grown until day 21 in M-CSF absence. A selective pressure for cell survival was initiated after withdrawal of M-CSF. The surviving cells were more prone to M2-like phenotype, even after receiving interleukin-4 (IL-4) stimulation. The transcriptome analysis unveiled that endogenous CSF-1 level was dramatically up-regulated and numerous genes downstream to CSF-1 covering tumor necrosis factor (TNF), ras-related protein 1 (Rap1) and phosphatidylinositol 3-kinase (PI3K)-protein kinase B (AKT) signaling pathway were significantly modulated, especially for proliferation, migration and adhesion. Moreover, the phenomenal increase of miR-21-5p and genes related to pro-tumor activity were observed in parallel. In summary, withholding of CSF-1/CSF-1R interaction would rather augment than suspend the M-CSF-driven pro-tumor activities of M2 macrophages in a long run.

The polarization status of porcine alveolar macrophages (PAMs) determines the infectivity of porcine reproductive and respiratory syndrome virus (PRRSV). PRRSV infection skews macrophage polarization toward an M2 phenotype, followed by T-cells inactivation. CD163, one of the scavenger receptors of M2 macrophages, has been described as a putative receptor for PRRSV. In this study, we examined two types of PRRSV-2-derived recombinant antigens, A1 (g6Ld10T) and A2 (lipo-M5Nt), for their ability to mediate PAM polarization and T helper (Th1) response. A1 and A2 were composed of different combination of ORF5, ORF6, and ORF7 in full or partial length. To enhance the adaptive immunity, they were conjugated with T cells epitopes or lipidated elements, respectively. Our results showed that CD163⁺ expression on PAMs significantly decreased after being challenged with A1 but not A2, followed by a significant increase in pro-inflammatory genes (TNF-α, IL-6, and IL-12). In addition, next generation sequencing (NGS) data show an increase in T-cell receptor signaling in PAMs challenged with A1. Using a co-culture system, PAMs challenged with A1 can induce Th1 activation by boosting IFN-γ and IL-12 secretion and TNF-α expression. In terms of innate and T-cell-mediated immunity, we conclude that A1 is regarded as a potential vaccine for immunization against PRRSV infection due to its ability to reverse the polarization status of PAMs toward pro-inflammatory phenotypes, which in turn reduces CD163 expression for viral entry and increases immunomodulation for Th1-type response.

Objective: The Baculovirus Expression Vector System (BEVS) is an established eukaryotic platform for high-yield recombinant protein production and is widely utilized for generating vaccine antigens, including recombinant classical swine fever virus E2 glycoprotein, African swine fever virus structural proteins (p72, p30, and p54), and porcine reproductive and respiratory syndrome virus envelope proteins GP5 and M. These antigens interact with macrophage-associated receptors, including CD163 and CD206, to modulate immune responses through macrophage polarization. However, whether baculovirus vector-derived components intrinsically influence macrophage polarization remains unclear, raising concerns regarding potential impacts on biological activity, vaccine efficacy, and downstream purification strategies. Methods: In this study, an M2-like tumor-associated macrophage (TAM) model capable of repolarizing toward an M1-like phenotype was established to distinguish the transcriptomic effects of the baculovirus vector control (VC) from those of the recombinant antigen (A1). Comparative RNA sequencing, Gene Set Enrichment Analysis (GSEA), functional enrichment analyses, and linear regression analysis were performed to evaluate vector- and antigen-associated transcriptional responses. Results: Comprehensive transcriptomic analysis showed that VC treatment induced only minimal transcriptomic alterations, with limited immune-related pathway enrichment and expression profiles that remained highly similar to those of untreated M2-like TAMs. Furthermore, linear regression analysis demonstrated negligible correlations between VC-induced and A1-induced transcriptional responses indicating that the limited changes associated with the vector backbone did not correspond to the receptor-mediated immune responses elicited by the recombinant antigen. In contrast, A1 stimulation induced distinct transcriptional reprogramming characterized by enrichment of pro-inflammatory and immune-activation pathways and a shift toward an M1-like macrophage phenotype. Conclusions: These findings suggest the negligible correspondence between VC- and A1-induced transcriptional profiles further supports the transcriptomic noises and signals of the baculovirus vector and inserted proteins, reinforcing its suitability as a platform for macrophage-targeted vaccine development while providing a basis for future optimization of downstream purification strategies.