Recombinant fragment of the lectin-binding region of Gal-3BP stimulates the expression of IL-6 in SARS-CoV-2 sensitive cells

A recent study posted to the Research Square* preprint server and under consideration at Scientific Reports investigated the impact of a recombinant fragment of cellular glycoprotein galectin-3-binding protein (Gal-3BP) on interleukin-6 (IL-6) expression in acute coronavirus disease 2019 (COVID-19).

Study: Galectin-3 binding protein stimulated IL-6 expression is impeded by antibody intervention in SARS-CoV-2 susceptible cell lines. Image Credit:Maryna Olyak/Shutterstock
Study: Galectin-3 binding protein stimulated IL-6 expression is impeded by antibody intervention in SARS-CoV-2 susceptible cell lines. Image Credit:Maryna Olyak/Shutterstock

Background

Various studies have reported an excessive production of IL-6 in patients suffering from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection in the acute phase, resulting in a hyperinflammatory condition characteristic of disease severity. However, an effective therapeutic approach for treating or preventing this inflammatory response in COVID-19 is lacking.

About the study

In the present study, researchers assessed the effect of D2, a recombinant fragment of the lectin-binding region of Gal-3BP, on the secretion of IL-6 during severe COVID-19. The team also assessed the impact of the anti-Gal-3BP monoclonal antibody 1959 on SARS-CoV-2 infected cell lines post-treatment with D2.

The team obtained HCC827 and A549 epithelial cell lines derived from human lung adenocarcinoma and Caco-2 epithelial cell lines, which in turn are derived from human colorectal adenocarcinoma. These cell lines were treated with different amounts of D2, anti-Gal-3BP monoclonal antibody 1959, and D-lactose. Cytokines were quantified 24 and 48 hours after incubation, and ribonucleic acid (RNA) extraction was performed.

The three cell lines were subsequently detached and treated with anti-human Gal-3 cells. Total RNA was isolated and quantified. The team converted the RNA to complementary deoxyribonucleic acid (cDNA). The samples were tested by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Subsequently, an enzyme-linked immunosorbent assay (ELISA) was performed to quantify IL-6 levels.

Out of the 585 amino acids present in the mature Gal-3BP, the team cleaved the first 18 amino acids using IL-6-specific primers, resulting in four distinct putative regions in the cDNA sequence, including the D2 domain consisting of beta-trace protein (BTP).

The team also generated a humanized variant of the murine monoclonal antibody, named antibody 1959, that recognized Gal-3BP. This antibody was produced by determining murine complementary determinant regions (CDRs) grafted on a human antibody framework, followed by purification and dialyzation of the antibody.

Results

The study results showed that treatment of the cell lines with D2 led to a dose-dependent improvement in IL-6 levels 24 hours after treatment in comparison to that of untreated cells. PCR analysis also showed that D2 efficiently stimulated the expression of IL-6 cells. Furthermore, 48 hours after treatment of the cells with D2, a substantial increase in IL-6 was noted in all three cell lines compared to the untreated cells. However, in the presence of lactose, a reduction in IL-6 levels was observed in D2-treated cells. This inhibitory effect of lactose on the IL-6 levels was proportional to Gal-3 levels as expressed by the cells and was notably higher in the HCC827 cells, followed by the A549 and Caco-2 cells.

The team observed a remarkable reduction in IL-6 secretion when treated with antibody 1959 post D2 treatment. They also noted an overexpression of Gal-3BP in COVID-19 symptomatic patients. Greater disease severity was associated with increased IL-6 levels. This over-secretion of Gal-3BP could activate higher levels of its endogenous ligand Gal-3, which could, in turn, lead to the production of inflammatory cytokines. 

Conclusion

The study findings showed that D2 successfully increased the secretion of IL-6 in cell lines susceptible to SARS-CoV-2 infection. Furthermore, this stimulatory effect of D2 was partially reversed by the treatment of anti-Gal-3BP monoclonal antibody 1959. Thus, the researchers believe that Gal-3 is an effective marker of severe COVID-19 and could serve as an effective target to reduce fatal inflammation and related organ damage in COVID-19 patients.

*Important notice

Research Square publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Bhavana Kunkalikar

Written by

Bhavana Kunkalikar

Bhavana Kunkalikar is a medical writer based in Goa, India. Her academic background is in Pharmaceutical sciences and she holds a Bachelor's degree in Pharmacy. Her educational background allowed her to foster an interest in anatomical and physiological sciences. Her college project work based on ‘The manifestations and causes of sickle cell anemia’ formed the stepping stone to a life-long fascination with human pathophysiology.

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