Question

please highlight some of the Innate and Adaptive Immune Defenses to Viral-mediated infections. Focus on what is known about the defenses against the positive-strand corona viruses and what is currently known.

Answer 1

Viral mediated infections are combated by the innate and adaptive immune responses by the body. Different kind of receptors of the innate immune response pathway are activated when the pathogen associated molecular patterns (PAMPs) like glycoproteins, lipopolysaccharide, nucleic acid motifs are regonised by the pattern recognition receptors on various cells. the three different kind of receptors RIG1 like receptors, Toll like Receptors and NOD like receptors sense the viral genomes ssRNA(single stranded RNA), dsRNA(double stranded RNA) and DNA. The RLRs recognise the RNA viruses and dendritic cells use TLRs to detect virus invasion.RLRs and TLRs help in the production of type I interferons and pro-inflammatory cytokines.

the coron avirus is a single stranded RNA virus. So its recognition is dependent on the RLRs and TLRs present in different cells. the toll like receptors are a family of receptors where the TLR-7 act to recognise the ssRNA virus containing guanosine and uridine rich sequences.this event of recognition takes place in the plasmacytoid dendritic cells and B cells. these dendritic cells secrete type I interferon on viral recognition. The TLRs in the dendritic cells bind to the viral genomic material remains in the endosome for long periods of time and thus allow for more robust downstream signaling to take place.

RNA virus upregulates Interferon expression via TLR7 and constitutively active TLR3. This leads to further activation of many cytokines and the NFKB pathway that leads to adaptive immune responses. type I interferon leads to increased expression of TLR3 and the activation of this in CD8alpha+ dendritic cells enhances the presentation of peptide fragments and thus are presented to the CD8+ T lymphocytes.

the antigen presentation by the dendritic cells also induce the T helper cells and they together activate the cytotoxic T lymphocyte to destroy the virl particles. This is the role of adaptive immune system

Thus both the innate and adaptive immune response together play a role in regonising and possible  killing of ssRNA virus like that of corona.