Evaluation of Free Light Chains (FLCs) Synthesis in Response to Exposure to SARS-CoV-2

Abstract

The aim of this study is to assess the synthesis of kappa (κ) and lambda (λ) free light chains (FLCs) in the serum of patients with COVID-19. All the 120 serum samples were collected from patients with COVID-19 and from healthy controls (vaccinated and non-vaccinated against SARS-CoV-2). FLCs, IgG total, IgG4, IgG anti-Nucleocapsid (N), anti-spike S1 receptor binding domain (S-RBD) antibodies and IL-6 were measured according to the manufacturers’ instructions. The concentrations of anti-N IgG, IgG total, IgG4 and IL-6 were elevated in the COVID-19 group in comparison to the vaccinated and non-vaccinated controls. The levels of anti-S-RBD IgG and κFLC were increased in COVID-19 and healthy vaccinated patients when compared to non-vaccinated controls. λFLC concentration was higher in the COVID-19 group than in the non-vaccinated group. The κ:λ ratio was lower in both COVID-19 and non-vaccinated groups in comparison to vaccinated controls. κFLC correlated with all tested parameters (anti-S-RBD IgG, anti-N IgG, λFLC, κ:λ ratio, IgG total, IgG4 and IL-6) except CRP, whereas λFLC correlated with all examined parameters except IgG4. Elevated levels of FLCs in COVID-19 and healthy vaccinated against SARS-CoV-2 patients, as well as the correlation between free light chains with specific anti-SARS-CoV-2 antibodies and IL-6, reflect hyperactivation of the immune system after contact with coronavirus. Furthermore, it seems that serum levels of FLCs might be used as predictive markers of COVID-19. Our findings suggest that free light chains are involved in SARS-CoV-2 infection. However, understanding the exact mechanism requires further investigation.

- Influence Mechanism of Serum Free Immunoglobulin Light Chain on Pulmonary Inflammatory Response and Serum Levels of Inflammatory Factors in Patients with Chronic Obstructive Pulmonary Disease

“…The binding of IgLC to human neutrophils was shown to induce the chemokine IL-8 (CXCL8). This suggests that IgLC could play a role in the pulmonary inflammatory response observed in COPD patients (20).…”

“…The researchers found that levels of IgLC were elevated in animals with emphysema and right heart enlargement caused by chronic cigarette smoke inhalation. In patients with moderate to severe COPD, increased serum levels of IgLC were found compared with controls (20). The binding of IgLC to human neutrophils was shown to induce the chemokine IL-8 (CXCL8).…”

Analysis of the Presence and Levels of IgG Antibodies Directed against the S1 Protein Receptor Binding Domain and the N Protein of SARS-CoV-2 in Patients with Multiple Sclerosis Treated with Immunomodulatory Therapies

“…The literature shows that the most specific and the least likely to cross-react antibodies are those directed against the S1 protein receptor binding domain, so we tested these antibodies in our research [ 26 ]. At visit 1, the presence of these antibodies was found in almost 82% of the study group.…”

Laboratory Diagnosis of Intrathecal Synthesis of Immunoglobulins: A Review about the Contribution of OCBs and K-index

“…Generally, a kFLC index cut-off equal to 4.7, compared to the OCB and IgG index, showed greater sensitivity (92.9%) but lower specificity (77.5%) [28]. In addition, considering the advantages regarding the use of the K-index (rapid and automated technique) compared to OCBs, some authors have proposed the use of the K-index as a primary marker instead of the evaluation of OCBs to highlight the intrathecal synthesis of IgG [3,28,38,61].…”