IL-10 boosts antibody sugar coating by countering IFNγ in germinal center B cells
In mice, blocking IL-10 signaling lowered IgG galactosylation and sialylation after Alum immunization, tied to reduced St6gal1 in germinal center B cells and plasma cells.
Résumé
IgG antibodies carry a sugar chain at Asn297 in the Fc region. Galactose and sialic acid on that chain shape how strongly antibodies drive inflammation. Inflammatory signals like IFNγ are known to strip these sugars, but less is known about what restores them. Mice immunized with ovalbumin and Alum, then given an IL-10 receptor-blocking antibody, produced antigen-specific IgG1 with less galactosylation and sialylation. Their germinal center B cells and plasma cells also expressed less of the sialylation enzyme St6gal1. Alum also produced many T follicular cells that made both IL-10 and IFNγ. In cultured mouse and human cells, IL-10 counteracted IFNγ-driven loss of St6gal1. The data show association rather than proof of cause. They point to IL-10 as a counter-regulator of antibody glycosylation, with possible relevance to vaccination and inflammatory disease.
Résumé détaillé
IgG antibodies carry a conserved sugar chain at Asn297 in the Fc region. The amount of galactose and sialic acid on this chain influences antibody effector functions, including how inflammatory or anti-inflammatory an antibody response is. Earlier work showed that strong inflammatory adjuvants and the cytokine IFNγ reduce galactosylation and sialylation, partly by lowering expression of the sialyltransferase St6gal1 in germinal center (GC) B cells and their plasma cell progeny. What pushes these modifications upward has been poorly understood. This study asked whether the anti-inflammatory cytokine IL-10 is part of that counter-regulation.
Mice were immunized with the model protein ovalbumin plus Alum, the least inflammatory adjuvant tested in earlier work, with or without an anti-IL-10 receptor blocking antibody given on day 3 to target the GC phase. On day 14 the researchers measured Fc glycosylation of antigen-specific serum IgG1 by nano-LC-MS and St6gal1 protein in antigen-specific IgG1-positive GC B cells and plasma cells by flow cytometry. They also profiled T follicular cells in IL-10 reporter mice, and tested IL-10 and IFNγ in cultured LPS-stimulated mouse splenic B cells and R848-stimulated human PBMCs.
IL-10 receptor blockade lowered galactosylation and sialylation of anti-Ova IgG1 and decreased St6gal1 in antigen-specific GC B cells and plasma cells. Across individual mice, Fc galactosylation and sialylation correlated strongly with St6gal1 levels. This is puzzling because Alum induced the highest frequency of IFNγ-producing T follicular cells on day 12, yet also the highest galactosylation and sialylation. IL-10 reporter mice resolved part of this: Alum produced the highest frequency and number of T follicular cells that made both IL-10 and IFNγ. In culture, IFNγ reduced St6gal1 and IL-10 counteracted that reduction in both mouse B cells and human PBMCs.
The authors propose that IL-10 from IL-10+IFNγ+ T follicular cells may offset IFNγ-mediated suppression of St6gal1. The result would be more galactosylated and sialylated long-term IgG. If confirmed, this could inform vaccine and adjuvant design and the study of antibody glycosylation changes in inflammatory and autoimmune disease.
Several caveats apply. IL-10R blockade was systemic and could affect many cell types, including early extrafollicular plasma cell responses. The study does not establish that the double-producing T follicular cells cause the glycosylation changes. It also did not determine whether IL-10 acts directly on B cells or indirectly. Other cytokines, other glycosyltransferases, and independent regulation of B4galt1 were not examined. The work is a short correspondence in mice and cell cultures, with small groups (n = 5), so human implications remain to be tested.
Principales conclusions
- Blocking IL-10 receptor after Ova-Alum immunization reduced galactosylation and sialylation of long-term antigen-specific IgG1 Fc in mice.
- IL-10R blockade lowered St6gal1 expression in antigen-specific IgG1+ germinal center B cells and plasma cells.
- Fc galactosylation and sialylation correlated strongly with St6gal1 levels across individual mice.
- Alum induced the most IL-10+IFNγ+ double-producing T follicular cells, despite also inducing high IFNγ-producing cells.
- IL-10 counteracted IFNγ-driven St6gal1 downregulation in cultured mouse B cells and human PBMCs.
Méthodologie
C57BL/6 mice were immunized intraperitoneally with ovalbumin and Alum, with or without anti-IL-10R antibody on day 3 (n=5 per group). Fc glycosylation was measured by nano-LC-MS, and St6gal1 by flow cytometry, with IL-10 reporter mice and ex vivo cultures of mouse B cells and human PBMCs. Statistics included t-tests, Kruskal-Wallis with Dunn's test, and two-way ANOVA.
Limites de l'étude
Systemic IL-10R blockade could act on multiple cell types, including extrafollicular responses, and a causal role for IL-10+IFNγ+ T follicular cells was not shown. Whether IL-10 acts directly on B cells was not tested, and other cytokines and B4galt1 were not examined. Findings come from small mouse groups and ex vivo cultures, so translation to humans is unproven.
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