Innate immune-mediated antiviral response to SARS-CoV-2 and convalescent sera a potential prophylactic and therapeutic agent to tackle COVID-19.

The whole world is confronting the pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Unfortunately, there is no vaccine to prevent novel coronavirus infection. Besides several experimental drugs, the strong immune responses and convalescent sera are the current two potential options to tackle coronavirus disease 2019 (COVID-19) infection. Innate immune-mediated antiviral responses are initiated by the recognition of viral invasion through pathogen-associated molecular patterns (PAMPs). In coronavirus, the PAMPs are recognized by Toll-like receptors 3 and 7, endosomal ribonucleic acid receptors, RNA in cytosol, and by pattern recognition receptor (RIG-1) in the alveolar cells and site of invasion. Nuclear factor-κB and interferon regulatory transcription factor (IRF3) are activated in response to the above recognition episode and translocate to nucleus. These transcription factors in the nucleus initiate the expression of interferon type 1 and pro-inflammatory cytokine storm, which leads to first line of defense at the site of viral entrance. The effectiveness of innate immune system is greatly relies on type 1 interferons and its cascade, because of their role in the inhibition of viral replication and initiation of adaptive immune responses. The successful interferon type 1 response put down the viral replication and transmission at prompt point. Passive immunization is the administering of antibodies into infected patients, which is taken from recovered individuals. The convalescent sera of the recovered COVID-19 patients are containing antiviral neutralizing antibodies and are used therapeutically for infected individuals by SARS-CoV-2 and for the purpose of prophylaxis in exposed individuals. The convalescent sera is found effective when administered early at the onset of symptoms.