Clinical Severity of Visceral Leishmaniasis Is Associated with Changes in Immunoglobulin G Fc N-Glycosylation

Abstract

Visceral leishmaniasis (VL) has a high fatality rate if not treated; nevertheless, the majority of human infections with the causative agent, Leishmania infantum chagasi, are asymptomatic. Although VL patients often present with increased levels of serum immunoglobulins, the contribution of antibodies to resistance or progression to disease remains unknown. Effector and regulatory functions of antibodies rely on their interactions with type I and II Fc receptors, and these interactions are tuned by the patterns of antibody Fc N-glycosylation. In view of these facts, we applied a robust method of IgG Fc N-glycopeptide profiling of serum samples from 187 patients with VL, 177 asymptomatic individuals, 116 endemic controls (individuals residing in areas where VL is endemic) and 43 nonendemic controls (individuals living in an area where VL is not endemic). We show that, in comparison to the overall IgG Fc N-glycan profiles of asymptomatic or uninfected healthy individuals, those of patients with VL are profoundly altered. These changes correlate with levels of serum cytokines and the inflammation marker C-reactive protein. We also fitted univariate and multivariate ordinal logistic regression models to demonstrate the ability of IgG Fc N-glycosylation features and immunity regulators present in serum to predict disease severity in VL patients. Importantly, we show that Fc N-glycosylation profiles change after treatment of VL. This study introduces important concepts contributing to the understanding of antibody responses in infections with Leishmania parasites and provides new insights into the pathology of human VL.

Blood Transcriptional Profiling Reveals Immunological Signatures of Distinct States of Infection of Humans with Leishmania infantum

“…As observed for experimental VL [43], our study supports the view of compartmentalized responses, i.e., the dynamics of dominant pathways in specific cells of the spleen, liver, bone marrow and peripheral blood might be differentially associated with pro-inflammatory or regulatory processes during the course of the infection. For instance, there are strong evidences that IL-10 plays a role in the suppression of the response in the spleen of VL patients [44,45], but, despite increased serum concentrations or production of IL-10 in whole blood assays [8,46] and elevated expression of IL-10 found herein by RT-qPCR, we were unable to identify an up-regulation of the "IL-10 signaling" pathway in the peripheral blood of VL patients. On the other hand, we did identify a negative regulation of "IL-10 signaling" pathway in the transcriptional profiles of patients under remission, which might correlate with decreased levels of this cytokine and recovery after therapy [47].…”

“…Indeed, neutropenia has been shown to be an independent risk factor for death in children with VL [56], indicating that the low proportion of circulating granulocytes and monocytes translate into the down-regulation of genes coding for chemokine receptors and chemokines as CCR1 , CXCR1 , CXCL8 or even neutrophil activation receptors as FPR1 , C5AR1 ; in contrast, the up-regulation of IFNG underscores the increased levels of IFN-γ present in serum from VL patients [8], whereas up-regulation of both IFNG and CXCL10 support the activation of T lymphocytes and development of a Th1 response during active disease [6]. Accordingly, we were unable to identify significant differences in the relative proportions of T lymphocytes from VL patients compared to other groups (Fig 5B), indicating that DEGs annotated into processes as TCR signaling were not influenced by the relative proportion of those cells.…”

“…Indeed, follicular T cell-mediated regulation of the B lymphocyte compartment may account for beneficial or pathogenic responses during distinct states of infection with L . infantum [68], a hypothesis that is supported by significant differences in structural and functional features of immunoglobulin G isolated from VL patients and asymptomatic individuals [8]. …”

“…These findings indicate that progression of VL involves other molecular mechanisms besides failures in activation and differentiation of CD4 + T lymphocytes. Development and severity of VL have been associated with several pro-inflammatory and immunoregulatory factors such as cytokines [7,8], lipopolysaccharide [9], mannan-binding lectin [10], C reactive protein and patterns of IgG Fc N-glycosylation [8]. In addition, studies addressing features of infected asymptomatic individuals point towards a fine regulation of several immune compartments thought to control parasites without damage to the host [8,11,12].…”

A Functional Role for Antibodies in Tuberculosis

“…These Fc effector functions are regulated immunologically via two features of the Ab Fc domain: 1) through Fc class-switch recombination selecting different isotypes (i.e., IgG, IgM, IgA, IgD, and IgE) and/or subclasses (e.g., IgG1, 2, 3, 4) and 2) the post-translational addition of distinct glycan species on the Fc domain of antibodies, specifically at asparagine 297 on IgG (Vidarsson et al, 2014). In particular, Ab glycosylation varies with age, sex, disease state, treatment, infection, and vaccination which likely reflect the highly sensitive and dynamic processes that actively alter Ab effector function during an inflammatory response (Ackerman et al, 2013; Gardinassi et al, 2014; Ho et al, 2014; Mahan et al, 2016; Parekh et al, 1989). …”