Question

Describe the cellular and humoral responses to viral (COVID-19) infection. Be sure to address the role of CD4 and CD8 cells, and the role of B cells and antibodies. What antibodies are produced in response to COVID-19 and when (approximately)?

Answer 1

Coronaviruses (SARS-CoV-2) are enveloped, nonsegmented, positive‐sense single RNA virus genomes in the size ranging from 26 to 32 kilobases, the largest known viral RNA genome. Coronavirus disease 2019 (COVID-19), a newly emerged respiratory disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) . Most patients with COVID-19 exhibit mild to moderate symptoms like fewer,dry cough,body pain etc , but some cases progress to severe pneumonia and about a few (5%) develop acute respiratory distress syndrome, septic shock and multiple organ failure.

Corona virus infection can activate innate and adaptive immune responses.  Uncontrolled inflammatory innate responses and impaired adaptive immune responses may lead to harmful tissue damage, both locally and systemically. In patients with severe COVID-19, lymphopenia (state where you have a reduced level of a certain type of blood cell called a lymphocyte) is a common feature, with drastically reduced numbers of CD4+ T cells, CD8+ T cells, B cells and natural killer as well as a reduced percentage of monocytes, eosinophils and basophils.  The detection of SARS-CoV-2-specific IgM and IgG in patients provided the basis for disease diagnosis.  Patients with severe disease frequently had an increased IgG response and a higher titre of total antibodies, which was associated with worse outcome.This can be due to possible antibody-dependent enhancement (ADE) of SARS-CoV-2 infection. Most patients with severe COVID-19 exhibit substantially elevated serum levels of pro-inflammatory cytokines including IL-6 and IL-1β, as well as IL-2, IL-8, IL-17, G-CSF, GM-CSF, IP10, MCP1, MIP1α and TNF, characterized as cytokine storm. C-reactive protein and D-dimer are found to be abnormally high. High levels of pro-inflammatory cytokines may lead to shock and tissue damage in the heart, liver and kidney, as well as respiratory failure or multiple organ failure.