Immunomodulation: Immunoglobulin Preparations Suppress Hyperinflammation in a COVID-19 Model via FcγRIIA and FcαRI

Abstract

The rapid spread of SARS-CoV-2 has induced a global pandemic. Severe forms of COVID-19 are characterized by dysregulated immune response and “cytokine storm”. The role of IgG and IgM antibodies in COVID-19 pathology is reasonably well studied, whereas IgA is neglected. To improve clinical outcome of patients, immune modulatory drugs appear to be beneficial. Such drugs include intravenous immunoglobulin preparations, which were successfully tested in severe COVID-19 patients. Here we established a versatile in vitro model to study inflammatory as well as anti-inflammatory processes by therapeutic human immunoglobulins. We dissect the inflammatory activation on neutrophil-like HL60 cells, using an immune complex consisting of latex beads coated with spike protein of SARS-CoV-2 and opsonized with specific immunoglobulins from convalescent plasma. Our data clarifies the role of Fc-receptor-dependent phagocytosis via IgA-FcαRI and IgG-FcγR for COVID-19 disease followed by cytokine release. We show that COVID-19 associated inflammation could be reduced by addition of human immunoglobulin preparations (IVIG and trimodulin), while trimodulin elicits stronger immune modulation by more powerful ITAMi signaling. Besides IgG, the IgA component of trimodulin in particular, is of functional relevance for immune modulation in this assay setup, highlighting the need to study IgA mediated immune response.

The Dual Role of a Polyvalent IgM/IgA-Enriched Immunoglobulin Preparation in Activating and Inhibiting the Complement System

“…This process, however, is inhibited at too high Ig concentrations (e.g., 20 mg/mL trimodulin, data not shown). This could be an assay-related effect due to FcR saturation of the neutrophils or via upregulation of inhibitory receptors on the HL-60 cells [48,59,60], but may also occur in vivo as suggested in Figure 5A-D in the absence of infection. It is possible that the rebound of C3 and C4 in the serum of the healthy subjects, after three of five consecutive dosages of trimodulin, was due to such saturation (Figure 5C,D).…”

“…Nevertheless, at 10 mg/mL phagocytosis was still significantly (p < 0.0001) increased as compared to the FB control. In the absence of active complement, the phagocytosis-stimulating activity of trimodulin is mostly IgG-and IgA-dependent, since the HL-60 cells exhibit both Fc-γ receptors (FcγR) as well as Fc-α receptors (FcαR) on their surface [48,54,55]. The IgM-binding Fc-µ receptor (FcµR) is not expressed.…”

“…Post hoc analysis revealed a high mortality benefit in sCAP patients with a strong inflammatory response who were treated with trimodulin compared to placebo. In addition to the relevant antimicrobial activities mediated by the three antibody isotypes present in the preparation, trimodulin was shown to have immunomodulatory functions [44,[47][48][49].…”

The Functional Role of IgA in the IgM/IgA-Enriched Immunoglobulin Preparation Trimodulin

“…Cells were adjusted to 6 × 10 5 cells/mL and cultured for 4 days at 37 • C [48]. Flow cytometry analysis confirmed cell phenotype, as described in our previous work [43].…”

“…In our previous work, we showed the immunomodulatory properties of trimodulin in a neutrophil COVID-19 model. We demonstrated superior immunomodulation by trimodulin in comparison to standard IVIG and attributed these effects to the additional IgA component of trimodulin [ 43 ]. We used the neutrophil-like HL-60 cell line because neutrophils have crucial functions in immunity and are—dependent on their potent effector functions—a main inducer of tissue damage when exhausted.…”