In immunology, some therapies have been used successfully for decades, yet their complete mechanisms remain surprisingly elusive. Intravenous immunoglobulin (IVIg), a pooled normal IgG from several thousand healthy donors, is one such therapy. Although extensive work has linked IVIG to modulation of Fc receptors, complement cascades, inflammatory cytokines, and immune cells functions and metabolism, the contribution of intracellular homeostatic pathways has received comparatively little attention. Our interest in this question emerged from a recurring observation made by our group: IVIG consistently induced autophagy in innate immune cells. This unexpected finding prompted us to ask whether autophagy induction might represent a broader, clinically relevant feature of IVIG-mediated immune regulation.
In the earlier work, our group showed that IVIG could activate macroautophagy in dendritic cells, M1 macrophages, and monocytes. Similar signatures were also confirmed in peripheral blood mononuclear cells of inflammatory myopathy patients treated with IVIG. The consistency of these observations sparked a deeper question: Is autophagy induction a broader and clinically relevant feature of IVIG therapy?
To explore this, we turned to publicly available single-cell transcriptomic data from patients with Kawasaki disease (KD), an acute inflammatory condition in which IVIG remains the first line of therapy. KD provided a compelling context because innate immune activation is central to its pathology. What began as an effort to validate our previous findings soon evolved into something much more expansive.
Rather than focusing immediately on autophagy genes, we first asked how innate immune cell populations themselves changed across healthy individuals, untreated KD patients, and those who had received IVIG. The data revealed a polarised inflammatory landscape in KD patients: expansion of classical and intermediate monocytes and low-density neutrophils, alongside a reduction in NK cells and γδ T cells. Following IVIG treatment, these shifts began to reverse, suggesting that IVIG was doing more than simply suppressing inflammation — it was reshaping the immune landscape.
The story became even more compelling when we examined how these cells communicated with one another. The immune system is not just a collection of independent cell types; it is a dynamic communication network. In KD, monocytes emerged as dominant signalling hubs, driving dense inflammatory interaction networks. After IVIG therapy, this tightly interconnected inflammatory web appeared to loosen. Communication patterns shifted toward a more balanced state. IVIG was not merely dampening signals — it was reorganising immune communication architecture.
When we returned to autophagy, the findings added another layer of complexity. We expected to see macroautophagy signatures, and indeed we did. But what emerged was far more nuanced. Different innate immune subsets exhibited distinct autophagy programmes: mitophagy signatures in monocytes and NK cells, aggrephagy in γδ T cells, xenophagy-related pathways in neutrophils, and non-canonical LC3-associated phagocytosis signals in non-classical monocytes. IVIG was not triggering a uniform cellular response; it was activating tailored, cell-type–specific autophagy pathways. That realisation marked a turning point in the project. IVIG appeared to function as a context-dependent immune recalibrator.
Perhaps the most satisfying aspect of this work was how it came full circle. What began as an experimental observation in primary innate immune cells was extended into patient-level transcriptomics and then returned to the bench for mechanistic validation. In vitro assays confirmed time-dependent LC3-II induction across multiple IVIG formulations, while Fc fragments and C-type lectin receptors were dispensable. Seeing transcriptional signatures in patients align with biochemical evidence of autophagy activation was deeply rewarding. It reinforced that what we had initially observed was not an artIfact of cell culture but a biologically relevant phenomenon occurring in treated patients.
This journey ultimately changed how we think about IVIG. Instead of viewing it solely through the lens of antibody-mediated immune modulation, we now see it as a therapy that engages intrinsic cellular homeostatic machinery. By activating selective autophagy pathways, IVIG may help restore mitochondrial quality control, limit inflammasome amplification, and rebalance immune communication networks.
For us, this project represents more than a collection of data and figures. It illustrates how a curious experimental observation can grow into a broader systems-level insight when bench science and computational analysis intersect. It was, truly, a beautiful scientific journey – and a reminder that even immunotherapies used for decades can still hold unexpected surprises.