The immunomodulatory properties of the IgM- and IgA-enriched immunoglobulin preparation trimodulin

Abstract

Severe infection diseases, like sepsis or sCAP, are well-known problems for public health. With the outbreak of SARS-CoV-2 and COVID-19, another infection disease with a dramatic impact on health and the economy comes into focus. Severe cases of sepsis, sCAP and COVID-19 lead to a dysregulated immune response associated with overwhelming inflammation. Modulation of the hyperinflammatory immune system is, therefore, a major goal of therapy. A promising option is the adjunctive therapy with trimodulin, an IgM- and IgA-enriched immunoglobulin preparation in clinical testing (comprising ~21 % IgM, 23 % IgA, and 56 % IgG). Available functional studies identify several modes of action, which were mainly attributed to the IgG or IgM component. In contrast, the role of IgA in these preparations was not unraveled yet. This thesis aim is to investigate the immunomodulatory properties of trimodulin in the context of severe infection diseases. A specific focus was set on the identification of functional roles for the additional IgA component. First, a cellular model system based on neutrophil-like HL-60 cells was established and comprehensively characterized. The induction of inflammation by bacterial stimuli (LPS and S.aureus) or by SARS-CoV-2-like particles was investigated and the underlying mechanism (FcR dependency, signaling pathways) identified. Next, anti-inflammatory effects of trimodulin on resting cells, as well as on inflammatory activated cells were analyzed. The following five synergistic mechanisms for immunomodulation by trimodulin were shown: (1) The direct binding of pro-inflammatory cytokines. (2) Targeting of ITAMi signaling by monomeric IgG and IgA species. (3) Activation of inhibitory ITIM signaling and increased FcγRIIB expression. (4) Modulation of cell phenotype by decreased FcγRIIA and FcαRI expression. (5) Displacement of immune complex and reduced phagocytosis. By comparing immunomodulatory effects to classical IVIg, trimodulin was shown to mediate stronger immunomodulation by better binding of cytokines, enhanced phenotype modulation, and activation of ITAMi signaling. Furthermore, the IgA component of trimodulin interacts with the FcαRI receptor and mediates FcαRI dependent phagocytosis of S.aureus. In conclusion, several synergistic modes of action are induced by trimodulin mediating powerful immunomodulation. Beneficial effects in comparison to IVIg can be attributed to the additional IgA component, by targeting FcαRI and inhibitory signaling. Differences in IgG subclass distribution and synergistic effects between monomeric and multimeric IgG, IgA, and IgM in trimodulin could be further reasons for improved immunomodulation by trimodulin. The in vitro models of this work depicting sepsis, sCAP and COVID-19 demonstrated potent immunomodulation of trimodulin. Nevertheless, these models are restricted by testing only one cell type and a limited number of cellular effector outcomes. Further work is necessary to extend the data set to further cell types and modes of action. Only with comprehensive knowledge about the modes of action in vitro, clinical data for sepsis, sCAP or COVID-19 patients can be supported and explained.