Deciphering the Immunological Landscape of SARS-CoV-2 Infection and Co-infection: Insights into Cytokines, Gene Expression, and Clinical Outcomes

Abstract

Coronavirus disease 2019 (COVID-19), originating from the novel human pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a severe ailment associated with widespread global morbidity and mortality. The immune response to SARS-CoV-2 infection involves the production and expression of numerous cytokines, playing a crucial role in determining the infection's outcome. This study aimed to explore the correlation between specific immune cytokines and the consequences of SARS-CoV-2 infection, as well as to identify key genes associated with the immune response against the virus. Transgenic mice expressing the human ACE2 receptor were chosen as they constitute a robust model for studying COVID- 19 infection, thoroughly mirroring the human infection. To complement animal modelling data, cytokine levels were measured in human serum samples. The role of IL-6 in the immune response was evaluated by measuring the potential impact of IL-6 blocking at different stages of the disease and using three variants of SARS-CoV-2 virus. Weight loss, viral loads in lungs and nasal turbinates, serum IL-6 level, and the histopathological analysis of the lungs were assessed. Anti-IL-6 antibody treatment demonstrated no effect on SARS-CoV-2 infected mice and may cause unfavourable outcomes when used early as a countermeasure in SARS-CoV-2 infection. Given the global impact and public health significance of the Influenza A virus (IAV), coupled with its capacity to infect a substantial number of individuals annually, its effect was studied with SAR-CoV-2 virus. The differentially expressed immune genes and the effects of a two-step infection involving IAV and SARS-CoV-2 were measured through samples obtained from a transgenic mouse model. These samples were collected at 6 dpi and 10 dpi and subjected to sequencing using the Illumina short-read length cDNA-PCR sequencing method. Co-infection caused more weight loss than SARS- CoV-2 single infection. The comparison between SARS-CoV-2 single infection and Co-infection revealed differentially expressed genes on both day 6 and day 10 post infection. Gene expression analysis indicated that influenza infection was primarily linked to the innate immune response, whereas SARS-CoV-2 infection was predominantly associated with the adaptive immune response. COVID-19 patients’ serum cytokines levels were assessed to find out whether there is a notable association between the severity of COVID-19 disease and the levels of specific cytokines. Patients who were asymptomatic had higher levels of IL-2Rα, IL-8, IL-18, IP-10, MCP-1, MIP-1β, and D-dimer compared to healthy subjects. Only MCP-1 changed between symptomatic patients and asymptomatic patients. Patients who were admitted to ICU and died had higher levels of IL-2Rα, IL-8, IP-10, MCP- 1, and CRP compared to those who were admitted to ICU and survived. Disease severity and elevated mortality observed in COVID-19 patients may result not only from SARS-CoV-2 virus infection but also from the immune response elicited by the infection.