Abstract
BackgroundAntibody Fc-driven engagement of macrophages is critical for evoking cellular activation and effector functions and influencing tumour-associated macrophage (TAM) recruitment. We previously reported that IgE class antibodies promote restriction of cancer growth in rodent models associated with significant TAM infiltration. However, the human macrophage-associated IgE-Fc Receptor (FcεR) axis remains unexplored. We investigated the effects of anti-tumour IgE stimulation on human macrophage activation.MethodsHuman blood monocyte-differentiated quiescent (M0), classically-(M1) and alternatively-(M2) activated macrophages were crosslinked with IgE and polyclonal antibodies to mimic immune complex formation. We examined surface marker expression, cytokine secretion, protein kinase phosphorylation and gene expression in IgE-stimulated macrophages and IgE antibody-dependent macrophage-mediated cytotoxicity (ADCC) against tumour cells.FindingsA proportion (40%) of M2 and (<20%) M0 and M1 macrophages expressed the high-affinity IgE receptor FcεRI. IgE crosslinking triggered upregulation of co-stimulatory CD80, increased TNFα, IFNγ, IL-1β, IL-12, IL-10, IL-13, CXCL9, CXCL11 and RANTES secretion by M0 and M2 and additionally enhanced MCP-1 by M2 macrophages. IgE-stimulated M1 macrophages retained secretion of pro-inflammatory cytokines. IgE crosslinking enhanced the FcεRI-dependent signalling pathway, including phosphorylation of the Lyn kinase, ERK1/2 and p38 in M2 macrophages and upregulated Lyn gene expression by M1 and M2 macrophages. Anti-tumour IgE engendered ADCC of cancer cells by all macrophage subsets.InterpretationIgE can engage and re-educate alternatively-activated macrophages towards pro-inflammatory phenotypes and prime all subsets to mediate anti-tumour functions. This points to IgE-mediated cascades with potential to activate immune stroma and may be significant in the clinical development of strategies targeting tumour-resident macrophages.
Highlights
Tumour-associated macrophages (TAMs) form a significant proportion of the immune cell infiltrate and are thought to play important⁎ Corresponding author at: St
We previously demonstrated that treatment with MOv18 I.E. a monoclonal human/chimeric antibody engineered with Fc regions of the IgE class and specific for a tumour-associated antigen (TAA) (Folate Receptor alpha, FRα), triggered an immune-activatory TNFα/MCP-1 axis in tumours, which resulted in recruitment of macrophages into tumour lesions and was associated with significantly-reduced tumour growth [9], in a syngeneic immunocompetent lung metastases rat model
Based on previous evidence that IgE can influence macrophage recruitment and activation in rodent models [9], we investigated whether IgE crosslinking of Fcε receptors on the surface of different human macrophage subsets could influence soluble mediator release (Fig. 2A): Pro-inflammatory cytokines TNFα, IFNγ, IL-12, IL-1β: Crosslinking of IgE led to a drastic increase in TNFα secretion in both M0 and M2 macrophages, while IgE did not affect the low TNFα levels produced by M1 cells (Fig. 2B)
Summary
Antibody Fc-driven engagement of macrophages is critical for evoking cellular activation and effector functions and influencing tumour-associated macrophage (TAM) recruitment. We investigated the effects of anti-tumour IgE stimulation on human macrophage activation. We examined surface marker expression, cytokine secretion, protein kinase phosphorylation and gene expression in IgE-stimulated macrophages and IgE antibody-dependent macrophage-mediated cytotoxicity (ADCC) against tumour cells. IgE crosslinking enhanced the FcεRI-dependent signalling pathway, including phosphorylation of the Lyn kinase, ERK1/2 and p38 in M2 macrophages and upregulated Lyn gene expression by M1 and M2 macrophages. Interpretation: IgE can engage and re-educate alternatively-activated macrophages towards pro-inflammatory phenotypes and prime all subsets to mediate anti-tumour functions. This points to IgE-mediated cascades with potential to activate immune stroma and may be significant in the clinical development of strategies targeting tumour-resident macrophages
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