Research progress of IFN - γ in immune regulation and disease treatment: from molecular mechanism to clinical translation

As the sole member of type II interferons, IFN-γ plays a central regulatory role in the immune system. Its biological functions extend far beyond its initially discovered antiviral effects, and it is now established that IFN-γ participates in the regulation of multiple immune responses, including both innate and adaptive immunity. At the molecular level, IFN-γ binds to its heterodimeric receptors IFNGR1/IFNGR2, activating the classical JAK-STAT signaling pathway and inducing the expression of hundreds of interferon-stimulated genes (ISGs). This process involves precise spatiotemporal regulation: at the receptor level, IFN-γ first binds to IFNGR1 with an affinity of approximately 10 nM, triggering conformational changes that recruit IFNGR2 to form a complete signal transduction complex; at the signal transmission level, mutual phosphorylation of JAK1 and JAK2 leads to phosphorylation of the Tyr701 site on STAT1, promoting nuclear translocation of STAT1 homodimers (γ-activated factor, GAF); at the gene regulation level, these transcription factors recognize specific DNA sequence elements (γ-activated sequences, GAS) to drive the expression of downstream target genes. Notably, recent studies have revealed significant non-classical pathways of IFN-γ signaling, including effects on cell fate decisions through pathways such as MAPK, PI3K-Akt, and NF-κB, greatly expanding our understanding of the functional complexity of IFN-γ.

The production and secretion of IFN-γ are tightly regulated at multiple levels. In terms of cellular sources, beyond traditional Th1 cells and NK cells, research has shown that novel immune cell subsets such as γδ T cells, NKT cells, and ILC1 can also produce IFN-γ, and IFN-γ from different sources may possess unique biological characteristics. From a regulatory perspective, transcription factors T-bet and STAT4 are key activators of IFN-γ expression, while cytokines such as IL-4 and IL-10 exert inhibitory effects. In terms of epigenetic regulation, the histone modification state (e.g., H3K4me3 and H3K27ac) at the IFNG gene locus directly influences its transcriptional activity. In secretion dynamics, immune cells employ specialized mechanisms such as synapse-like secretion and lysosome-associated secretion to achieve targeted release and local concentration gradients of IFN-γ. This precise spatiotemporal regulation is critical for ensuring the accuracy and effectiveness of immune responses. The latest single-cell analysis techniques reveal that IFN-γ secretion exhibits a pulsatile pattern, with each activation cycle lasting approximately 6–8 hours, a dynamic feature that may be closely related to the formation and maintenance of immune memory.

The immunoregulatory functions of IFN-γ are evident at multiple levels. In innate immunity, IFN-γ is a key inducer of classical macrophage activation, upregulating iNOS expression to promote the production of reactive nitrogen intermediates, significantly enhancing the ability to kill intracellular pathogens. Simultaneously, IFN-γ also enhances the cytotoxic activity of NK cells by regulating the expression of surface activation receptors such as NKG2D and DNAM-1. In adaptive immune responses, IFN-γ not only promotes Th1 cell differentiation, forming a positive feedback loop, but also enhances the cytotoxic function of CD8+ T cells, stimulating the secretion of granzymes and perforin. Furthermore, IFN-γ significantly improves antigen presentation efficiency by inducing the expression of MHC class I and II molecules, a role particularly important in tumor immune surveillance and infection immunity. Notably, IFN-γ also modulates B cell function, promoting antibody class switching to subtypes such as IgG2a and IgG3, which have stronger opsonizing effects. From the perspective of systemic immunity, IFN-γ can regulate the migration and localization of immune cells by influencing the production of chemokines and the expression of adhesion molecules, thereby serving as a hub in inflammatory responses and tissue repair.

In the context of disease development, IFN-γ exhibits complex dual roles. In antitumor immunity, substantial clinical evidence supports the central role of IFN-γ: intratumoral injection in melanoma patients has shown that IFN-γ can achieve an objective response rate of 40%; BCG immunotherapy for bladder cancer has been confirmed to depend on IFN-γ-activated macrophage responses; and the efficacy of immune checkpoint inhibitors is significantly positively correlated with the activity of the IFN-γ signaling pathway. However, in autoimmune diseases, excessive IFN-γ production may lead to pathological damage, such as promoting synovial inflammation in rheumatoid arthritis, exacerbating demyelination in multiple sclerosis, and driving abnormal proliferation of keratinocytes in psoriasis. This duality is also evident in infectious diseases: on the one hand, IFN-γ-deficient patients exhibit nearly a hundredfold increased susceptibility to Mycobacterium tuberculosis; on the other hand, persistent IFN-γ signaling during chronic viral infections may lead to T cell exhaustion. Understanding these context-dependent functional differences is crucial for developing targeted IFN-γ therapeutic strategies.

Building on in-depth knowledge of IFN-γ's biological functions, multiple targeted intervention strategies have been developed. Among agonists, recombinant IFN-γ (brand name Actimmune®) has been approved for the treatment of chronic granulomatous disease, and its PEGylated derivatives can significantly extend half-life. New-generation cytokine prodrugs designed for tumor microenvironment-specific activation hold promise for improving therapeutic indices. Among antagonists, anti-IFN-γ monoclonal antibodies (e.g., Fontolizumab) have shown efficacy in phase II clinical trials for Crohn's disease, while soluble receptors (e.g., AMG 811) can effectively neutralize overactivated IFN-γ. Of particular interest are combination strategies, such as the co-administration of IFN-γ and PD-1 inhibitors, which can significantly enhance T cell tumor infiltration, and oncolytic virus vector-mediated local IFN-γ expression, which can boost antitumor immunity while reducing systemic toxicity. The development of these therapeutic approaches fully reflects the complete innovation chain from basic research to clinical translation.

The field of IFN-γ research still faces numerous challenges and opportunities. In terms of basic mechanisms, key scientific questions remain to be addressed, such as deciphering the spatiotemporal dynamics of IFN-γ signaling pathways, elucidating the heterogeneity of IFN-γ responses across different cell types, and uncovering the cross-regulatory networks between IFN-γ and other cytokines. In translational applications, the development of novel delivery systems capable of precisely modulating the intensity and spatiotemporal distribution of IFN-γ activity, the establishment of biomarkers to predict therapeutic responses, and the optimization of combination therapy designs will directly impact clinical outcomes. Special attention should be paid to breakthrough possibilities brought by emerging technologies: single-cell multi-omics analysis can comprehensively reveal cellular heterogeneity in IFN-γ responses; synthetic biology methods can construct intelligently responsive IFN-γ secretion systems; and nanocarrier technologies can achieve tissue-specific IFN-γ delivery. The intersection of these cutting-edge technologies with traditional immunology will open new avenues for the clinical application of IFN-γ. Overall, IFN-γ research has evolved from the initial characterization of an antiviral factor to a systematic analysis of immune regulatory networks. Through multidisciplinary collaborative innovation, more precise immune interventions may be achieved in the future, offering new options for the treatment of various diseases.