Oscar Campetella

Trypanosoma cruzi , the causative agent of Chagas disease, relies on surface sialylation to evade host immunity and invade cells. This process is mediated by trans -sialidases (TS) and mucins, an enzyme–substrate pair anchored to distinct lipid environments. Yet, how these molecules are organized at the nanoscale in the parasite’s membrane remains unknown. Using dual-color super-resolution microscopy, we show that ∼60% of mucins and TS are segregated into nanoclusters (∼100 nm) that rarely contact each other, distributed with a non-random separation distance, indicating that these abundant domains follow a specific order in the plasma membrane and are unlikely to serve as primary sites of sialylation. In contrast, the ∼40% fraction of non-clustered mucins and TS exhibits significantly shorter-than-random separation distances and appear ordered as in a shared fibrillar network. Additionally, we describe a distinct structural organization within these domains: mucins —residents of detergent-resistant domains (DRDs)—organize into high-molecular-weight complexes, whereas TS (which are excluded from DRDs) do not. This reveals an additional layer of membrane asymmetry and suggests a potential mechanism for domain-specific protein localization. Together, these findings uncover major principles of T. cruzi surface organization, with important implications for the regulation of host–parasite interactions.

Galectins (Gals), a family of mammalian lectins, have emerged as key regulators of the immune response, being implicated in several physiologic and pathologic conditions. Lately, there is increasing data regarding the participation of Galectin-8 (Gal-8) in both the adaptive and innate immune responses, as well as its high expression in inflammatory disorders. Here, we focus on the pro- and anti-inflammatory properties of Gal-8 and discuss the potential use of this lectin in order to shape the immune response, according to the context.

Trypanosoma cruzi, the protozoan agent of Chagas disease, has evolved an innovative metabolic pathway by which protective sialic acid (SA) residues are scavenged from host sialylglycoconjugates and transferred onto parasite surface mucin-like molecules (or surface glycoconjugates from host target cells) by means of a unique trans-sialidase (TS) enzyme. TS-induced changes in the glycoprotein sialylation profile of both parasite and host cells are crucial for the establishment of a persistent T. cruzi infection and for the development of Chagas disease-associated pathogenesis. In this chapter, we describe a novel metabolic labeling method developed in our labs that enables straightforward identification and molecular characterization of SA acceptors of the TS-catalyzed reaction.

TolT was originally described as a Trypanosoma cruzi molecule that accumulated on the trypomastigote flagellum bearing similarity to bacterial TolA colicins receptors. Preliminary biochemical studies indicated that TolT resolved in SDS-PAGE as ~3–5 different bands with sizes between 34 and 45 kDa, and that this heterogeneity could be ascribed to differences in polypeptide glycosylation. However, the recurrent identification of TolT-deduced peptides, and variations thereof, in trypomastigote proteomic surveys suggested an intrinsic TolT complexity, and prompted us to undertake a thorough reassessment of this antigen. Genome mining exercises showed that TolT constitutes a larger-than-expected family of genes, with at least 12 polymorphic members in the T. cruzi CL Brener reference strain and homologs in different trypanosomes. According to structural features, TolT deduced proteins could be split into three robust groups, termed TolT-A, TolT-B, and TolT-C, all of them showing marginal sequence similarity to bacterial TolA proteins and canonical signatures of surface localization/membrane association, most of which were herein experimentally validated. Further biochemical and microscopy-based characterizations indicated that this grouping may have a functional correlate, as TolT-A, TolT-B and TolT-C molecules showed differences in their expression profile, sub-cellular distribution, post-translational modification(s) and antigenic structure. We finally used a recently developed fluorescence magnetic beads immunoassay to validate a recombinant protein spanning the central and mature region of a TolT-B deduced molecule for Chagas disease serodiagnosis. This study unveiled an unexpected genetic and biochemical complexity within the TolT family, which could be exploited for the development of novel T. cruzi biomarkers with diagnostic/therapeutic applications. Chagas disease, caused by the protozoan Trypanosoma cruzi, is a lifelong and debilitating neglected illness of major significance in Latin America, for which no vaccine or adequate drugs are yet available. Identification of novel biomarkers able to transcend the current limits of diagnostic and/or therapeutic assessment methods hence surfaces as a main priority in Chagas disease applied research. In this framework, we herein undertook a thorough biochemical and antigenic characterization of T. cruzi TolT surface antigens. Our results unveil an unexpected complexity within this family, with at least 12 polymorphic TolT genes in the T. cruzi CL Brener reference strain genome. According to structural features, TolT deduced molecules could be split into three robust groups that show differences in their structural features, expression profile, sub-cellular distribution, post-translational modification(s) and antigenic structure. Overall, we show that TolT molecules are conspicuously expressed by both major mammal-dwelling stages of the parasite, and that they are differentially recognized by the immune system in Chagasic patients and in T. cruzi-infected mammals. Our findings are discussed in terms of the evolution and possible structural/functional roles of TolT molecules, as well as in terms of their applicability in Chagas disease serodiagnosis.

Summary: Galectin‐8 (Gal‐8) is a mammalian lectin endowed with the ability to co‐stimulate antigen‐specific immune responses. We have previously demonstrated that bone‐marrow‐derived dendritic cells produce high levels of interleukin‐6 (IL‐6) in response to Gal‐8 stimulation. As IL‐6 is a pleiotropic cytokine that has a broad effect on cells of the immune system, we aimed to elucidate whether IL‐6 was involved in Gal‐8‐dependent co‐stimulatory signals during antigen recognition by specific CD4 T cells. With this aim, splenocytes from DO11.10 mice were incubated with a low dose of the cognate ovalbumin peptide in combination with Gal‐8. Interleukin‐6 was found significantly increased in cultures stimulated with Gal‐8 alone or Gal‐8 plus cognate peptide. Moreover, IL‐6 signalling was triggered during Gal‐8‐induced co‐stimulation, as determined by phosphorylation of signal transducer and activator of transcription 3. Interleukin‐6 blockade by neutralizing monoclonal antibody precluded Gal‐8 co‐stimulatory activity but did not affect the antigen‐specific T‐cell receptor activation. Different subsets of dendritic cells, as well as macrophages and B cells, were identified as the cellular source of IL‐6 during Gal‐8‐induced co‐stimulation. To confirm that IL‐6 mediated the Gal‐8 co‐stimulatory effect, antigen‐presenting cells from IL‐6‐deficient or wild‐type mice were co‐cultured with purified CD4 T cells from OTII mice in the presence of cognate peptide and Gal‐8. Notably, Gal‐8‐induced co‐stimulation, but not the antigen‐specific response, was significantly impaired in the presence of IL‐6‐deficient antigen‐presenting cells. In addition, exogenous IL‐6 fully restored Gal‐8‐induced co‐stimulation. Taken together, our results demonstrate that IL‐6 signalling mediates the Gal‐8 immune‐stimulatory effect.

Germinal centers (GC) are important sites for high-affinity and long-lived antibody induction. Tight regulation of GC responses is critical for maintaining self-tolerance. Here, we show that Galectin-3 (Gal-3) is involved in GC development. Compared with WT mice, Gal-3 KO mice have more GC B cells and T follicular helper cells, increased percentages of antibody-secreting cells and higher concentrations of immunoglobulins and IFN-γ in serum, and develop a lupus-like disease. IFN-γ blockade in Gal-3 KO mice reduces spontaneous GC formation, class-switch recombination, autoantibody production and renal pathology, demonstrating that IFN-γ overproduction sustains autoimmunity. The results from chimeric mice show that intrinsic Gal-3 signaling in B cells controls spontaneous GC formation. Taken together, our data provide evidence that Gal-3 acts directly on B cells to regulate GC responses via IFN-γ and implicate the potential of Gal-3 as a therapeutic target in autoimmunity.