Treatment & Immune Responses_old
Our bodies have two types of immune responses: innate and adaptive. The innate immune response is rapid, non-specific, and triggers the adaptive immune response. In turn, the adaptive immune response identifies particular pathogens, creates antibodies to attack those pathogens, and provides lasting immunity to the specific pathogens. COVID-19 treatments work by mimicking and bolstering these evolved immune response mechanisms.
Video: Immune Responses to SARS-CoV-2
Immune responses to COVID-19
Innate immune response
The innate immune response is triggered when any pathogen is detected. This response is performed by three types of white blood cells: dendritic cells, mast cells, and phagocytes. Dendritic cells are common in the lungs, nose, stomach, and skin so they are usually the first white blood cells to detect a pathogen. These cells trigger the adaptive immune system by presenting pathogens to B and T cells. Mast cells release histamine when a pathogen such as a SARS-CoV-2 virus is detected, which causes blood vessels to expand and summons other white blood cells to the vicinity. This area will become inflamed, and if large areas of the body become inflamed, may cause a fever. Phagocytes are large white blood cells that envelope and destroy pathogens and dead host cells.
Adaptive immune response
The adaptive immune response is triggered by the innate immune response and is performed by four types of white blood cells: helper T-cells, killer T-cells (also called cytotoxic T-cells), plasma B-cells, and memory B-cells.
When a SARS-CoV-2 virus is presented to a T-cell, it identifies the spike protein. When the same spike protein is detected by a helper T-cell, it will release specialized cytokine molecules, triggering inflammation. When helper T-cells or mast cells cause inflammation, heat shock proteins on killer T-cells are activated, allowing the killer T-cells to ‘stick’ to the infected areas. When a killer T-cell detects a virus, it can release cytotoxic compounds that destroy its target, or it may bind and destroy a cell infected with the virus.
When a SARS-CoV-2 spike protein is presented to a B-cell, the B-cell will create specialized antibodies that can bind to the spike protein. Plasma B-cells circulate throughout the body and release antibodies to bind to spike proteins when a virus is detected. After the infection is over, the plasma B-cells will no longer produce these antibodies. Memory B-cells and their antibodies remain in the host long after infection. When the host is reinfected with the same virus, the memory B-cells will quickly and efficiently detect the spike protein and trigger the adaptive immune response immediately. This usually results in the pathogens being destroyed by the immune system before the host cells are infected and viral replication has begun and is the basis for long-lasting immunity.
Video: COVID-19 Vaccines
COVID-19 vaccines
The two major types of COVID-19 vaccines are mRNA vaccines such as the Pfizer-BioNTech and Moderna vaccines, and viral vector vaccines such as the Johnson & Johnson and AstraZeneca vaccines. An mRNA vaccine includes a lipid nanoparticle that allows the mRNA to enter human cells. This mRNA codes for the SARS-CoV-2 spike protein. Ribosomes in the human cells translate the mRNA into spike proteins. Viral vector vaccines rely on an adenovirus to transport DNA coding for the spike protein into human cells. Once in the cell, the DNA is transcribed to mRNA in the nucleus, and the mRNA is translated into spike proteins by the ribosomes. Both types of vaccines result in human cells producing SARS-CoV-2 spike proteins.
These spike proteins are then presented to memory B-cells, which in turn produce antibodies that are specialized to attach to the SARS-Cov-2 spike protein. Since memory B-cells will trigger a rapid adaptive immune response when a SARS-CoV-2 virus is detected, the host is more likely to experience less severe symptoms than if they had not been vaccinated.
Treatments
Monoclonal antibodies have been effective in treating patients with life threatening COVID-19 infections. These are the same as the antibodies that are be created by B-cells. When injected into a patient, they antibodies attach to SARS-CoV-2 spike proteins, not allowing the virus to infect host cells and identifying the virus as a threat to other white blood cells. Similar treatments are also used to combat autoimmune diseases and some forms of cancer.
Worksheet Questions Discussion Questions References Worksheet Questions
- Compare the function of the following cell types:
i) Killer T cells and Helper T cells
ii) Plasma B cells and Memory B cells - One hypothesis that explains the pathology of “long-COVID” sufferers is a process called mast-cell activation syndrome (MCAS). This causes mast cells to stay active even when there are no pathogens present. Based on the function of mast cells, explain why this condition may cause uncomfortable symptoms in those who suffer from it.
- Explain why dendritic cells are most common on surfaces such as the skin and upper airway. In your answer, be sure to describe the function of dendritic cells.
- Why might we be concerned about the evolution of a vaccine-resistant coronavirus strain?
- What are the major differences between mRNA and adenovirus based COVID-19 vaccines?