A student in the classroom has tested positive for COVID and has been asked to quarantine for two weeks. The student tested positive again for the same virus three months after returning to school.
Explain in a 300-words how his innate and adaptive immune response reacted at the first encounter with the virus. Make sure to include all cells, tissue, and cytokines … that you learned in this chapter. Then explain how the body responds differently to 2nd encounter of the same virus.
Hint: think about memory cells.
When the student was first exposed to the COVID-19 virus, their innate immune response was the first line of defense. The epithelial cells of the respiratory tract acted as a physical barrier, preventing viral entry. If the virus breached this barrier, macrophages, dendritic cells, and neutrophils recognized the pathogen-associated molecular patterns (PAMPs) on the virus through pattern recognition receptors (PRRs) such as toll-like receptors (TLRs). These immune cells triggered an inflammatory response, releasing cytokines like interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-α), which promoted fever and recruited more immune cells. Natural killer (NK) cells helped by killing infected cells, and complement proteins assisted in neutralizing the virus.
The adaptive immune response was activated when antigen-presenting cells (APCs), such as dendritic cells, presented viral antigens to naïve T cells in the lymph nodes. Helper T cells (CD4+) released cytokines like interferon-gamma (IFN-γ), stimulating cytotoxic T cells (CD8+), which targeted and destroyed infected cells. Additionally, B cells were activated and differentiated into plasma cells, producing antibodies (IgM and later IgG) specific to the virus, neutralizing it and preventing further spread. Some B and T cells became memory cells, ensuring a faster response to future infections.
Upon reinfection, three months later, the memory B and T cells rapidly recognized the virus, leading to a much faster and stronger secondary immune response. Memory B cells quickly produced high-affinity IgG antibodies, neutralizing the virus before it could establish an infection. Memory T cells, especially CD8+ cytotoxic T cells, rapidly destroyed infected cells. Because of this heightened response, the viral load was reduced more quickly, and symptoms were often less severe or absent. This adaptive immunity prevents reinfection or significantly lessens the disease severity upon re-exposure.