key: cord-0718457-za8qj08o
authors: Ganigara, Madhusudan; Sharma, Chetan; Bayry, Jagadeesh
title: Unraveling the mechanisms of IVIG immunotherapy in MIS-C
date: 2021-09-30
journal: Cell Rep Med
DOI: 10.1016/j.xcrm.2021.100431
sha: de1ff0a5bad1ca4cc11a762928b11fabd3cfc1cc
doc_id: 718457
cord_uid: za8qj08o

In The Journal of Clinical Investigation, Zhu et al. report that intravenous immunoglobulin (IVIG) targets IL-1β+ neutrophils to exert anti-inflammatory effects in Multisystem Inflammatory Syndrome in Children (MIS-C), a post-infectious inflammatory condition associated with the COVID-19.

Though SARS-CoV-2 infection in children is either mild or asymptomatic, in some children it is associated with the development of a post-infectious, serious inflammatory condition called Multisystem Inflammatory Syndrome in children (MIS-C). 1 MIS-C is characterized by immune dysregulation and cytokine storm, and the disease has overlapping features of myocarditis, toxic shock syndrome and Kawasaki disease (KD), a common acute febrile childhood vasculitis.

While there is considerable acute morbidity with MIS-Cnearly two-third of patients need intensive care treatmentmortality is low (1.9%) and short-term outcomes are favourable. 1 Due to the novelty of the syndrome and its similarity to KD, most centres have extrapolated KD guidelines for the clinical management of MIS-C. 2 Our understanding of molecular mechanism(s) that trigger MIS-C is still evolving however, some studies have suggested a possible role of IL-1 family signaling intermediates triggering a hyper-inflammatory response. To understand the pathogenesis of MIS-C and the source of IL-1β, Zhu et al. compared the expression of IL-1β in various immune cells of MIS-C patients, KD and febrile controls. 3 Intracellular flow cytometry using human IL-1β-specific monoclonal antibodies indicated that IL-1β + leukocytes were highly predominant in KD followed by MIS-C. Further dissection of the signature of the immune cells identified neutrophils as a major source of IL-1β.

Analyses of RNA in MIS-C neutrophils also confirmed high expression of IL-1β but not IL-1α.

It should be noted that the increased percentage of IL-1β + neutrophils was not specific for either KD or MIS-C and was also observed in febrile controls. Therefore, it appears that enhancement of IL-1β + neutrophils is a common feature of pediatric inflammatory conditions. IVIG as first-line therapy in MIS-C patients. 2 After treatment with IVIG, Zhu et al. noted more than 50% reduction in the neutrophil counts and more than 90% reduction in IL-1β-expressingneutrophils in both KD and MIS-C groups. 3 This remarkable effect persisted even when the analysis was confined to patients who received IVIG as the only immunomodulating medication in either group. Additionally, there was a reduced expression of neutrophil activation and adhesion markers indicating that IVIG targets IL-1β + neutrophils to ameliorate the inflammation in these two inflammatory conditions (Figure 1) . Thus, by demonstrating the vital role of IL-1 in the pathogenesis of KD and MIS-C, this study adds evidence for the use of anakinra, an IL-1 receptor antagonist, in patients refractory to therapy with IVIG or steroids. 2 Neutrophil death is crucial for the resolution of granulocyte-mediated inflammation. The authors aimed to identify the mechanisms of IVIG-induced neutrophil death using in vitro chemical inhibitors and live cell imaging. They found that IVIG-induced neutrophil cell death was blocked by PI3-kinase and NADPH oxidase inhibitors but not with pan-caspase inhibitors indicating that IVIG-induced cell death does not occur via apoptosis and caspase-1-dependent pyroptosis, necroptosis and ferroptosis. 3 This report thus identifies that IVIG and its F(ab') 2 fragments exert cytotoxic effects on neutrophils from the patients with inflammatory disorders via PI3-kinase and NADPH oxidase-dependent pathways. Previous in vitro experiments based on the cells isolated from healthy donors, have shown that IVIG induces neutrophil death both via caspase-dependent and -independent pathways, mediated via antibodies to Fas and Siglec-9 respectively. 8 Under the influence of inflammatory cytokines, IVIG induced a caspase-independent neutrophil death via NADPH oxidase pathway. 8 Both KD and MIS-C patients display enhanced levels of various proinflammatory cytokines that explain observed caspase-independent cytotoxic effects of IVIG on J o u r n a l P r e -p r o o f neutrophils. Of note, the morphology of neutrophils that underwent caspase-independent cell death resembled that of autophagolysosomal death 8 and recently IVIG has been shown to induce autophagy in the peripheral blood mononuclear cells by F(ab') 2 -and PI3-kinase-dependent pathways. 9 As, IVIG-induced neutrophil cell death in KD and MIS-C patients was also dependent on PI3-kinase, future investigation should aim at further dissection of this pathway.

Does this report explain all the possible mechanisms of IVIG in MIS-C? As correctly pointed out by the authors, the report provides one of multiple IVIG mechanisms that might be responsible for the amelioration of inflammation and pathology in MIS-C. Current evidence shows that various markers of inflammation are decreased in MIS-C patients following IVIG therapy. 4 In fact, IVIG has been shown to suppress the activation of T cells, monocytes, dendritic cells and also endothelial cells 7 that are activated in MIS-C. Also, nonspecific activation of B cells with autoimmune signatures were observed in MIS-C, 5 and IVIG could check B cell activation. 7 Although IVIG has been reported to suppress superantigen-mediated lymphocyte activation, that mechanism might not be responsible for the efficacy of IVIG in these MIS-C patients as pre-COVID-19 pandemic IVIG preparations do not have anti-SARS-CoV-2 antibodies. 10 There are limitations of the study, most notably the choice of a small sample size between groups, chosen for convenience, rather than powered for statistical analysis. The authors must be commended for the extensive immune analysis performed; however, there is inconsistency in the number of subjects between groups. Only two KD subjects underwent mass cytometry. Lastly, 'febrile control' was not well defined. While the reader is asked to assume that this group consists of common childhood febrile illnesses, this group could include anyone with a common J o u r n a l P r e -p r o o f cold to a malignancy, potentially confounding the study's findings. Pediatric COVID-19 patients without MIS-C would have made an ideal comparison.

The big picture of molecular mechanisms that lead to MIS-C in select SARS-CoV-2 exposed children remains unknown. This article suggests that neutrophils and IL-1β are the important players of pathogenesis of MIS-C. A randomized clinical trial in MIS-C would be useful to validate the findings but with uncertainty over the COVID-19 pandemic, it might be difficult to recruit sufficient patients at single centers and international collaboration might be required.

Further work on identifying the specific pathways IVIG utilizes to suppress the inflammation in MIS-C is needed and may allow us to edit dosages specific to clinical conditions being treated, and effectively use adjunct therapies such as steroids and other biological immunomodulators. 

Similarities and differences between COVID-19-related multisystem inflammatory syndrome in children and Kawasaki disease

American College of Rheumatology clinical guidance for multisystem inflammatory syndrome in children associated with SARS-CoV-2 and hyperinflammation in pediatric COVID-19: Version 2

Immune response to intravenous immunoglobulin in patients with Kawasaki disease and MIS-C

The innate and adaptive immune landscape of SARS-CoV-2-associated multisystem inflammatory syndrome in children (MIS-C) from acute disease to recovery

Humoral signatures of protective and pathological SARS-CoV-2 infection in children

Kawasaki disease: pathophysiology and insights from mouse models

IVIG-mediated effector functions in autoimmune and inflammatory diseases

Granulocyte death mediated by specific antibodies in intravenous immunoglobulin (IVIG)

Intravenous immunoglobulin mediates anti-inflammatory effects in peripheral blood mononuclear cells by inducing autophagy

No SARS-CoV-2 neutralization by intravenous immunoglobulins produced from plasma collected before the 2020 pandemic