All Types of Vaccines, How They Work, Animation.
Summary
TLDRThis video explains the process of how viruses infect human cells and how the immune system responds. It covers how viruses use host cells to replicate, the role of dendritic cells and T-cells in activating immune responses, and the different types of immunity. The script also discusses how vaccines work, comparing attenuated, inactivated, subunit, DNA, and mRNA vaccines, while highlighting their benefits, risks, and mechanisms of action. Special attention is given to the role of viral vectors and concerns surrounding DNA vaccines.
Takeaways
- 🦠 During a viral infection, the virus attaches to a human cell and uses the host cell’s machinery to replicate, producing new viral particles.
- 💥 The infected host cell dies, releasing new viral particles that infect more cells, causing tissue damage and symptoms.
- 🛡️ Infected cells present viral antigens on their surface, alerting the immune system and activating cytotoxic T-cells.
- 🌍 Dendritic cells act as professional antigen-presenting cells, capturing antigens and presenting them to helper T-cells in lymph nodes.
- 🤝 The immune system mounts two types of immunity: cell-mediated immunity and antibody-mediated immunity, but this process takes time.
- 💉 Vaccines introduce viral antigens to trigger immune responses without causing the disease, mimicking the natural infection response.
- ⚖️ Different types of vaccines exist, such as inactivated (Sinovac), subunit (EpiVacCorona), and nucleic acid (Pfizer, Moderna) vaccines, each with distinct mechanisms.
- 🧬 DNA vaccines introduce viral DNA into the cell's nucleus to generate viral antigens, while mRNA vaccines deliver mRNA that is translated into viral proteins in the cytoplasm.
- 🚫 Subunit vaccines cannot cause disease but may require adjuvants to stimulate the immune system, while nucleic acid vaccines raise concerns about DNA integration, though risks are minimal.
- 🔬 mRNA vaccines are less likely to integrate into the human genome and are delivered within a lipid covering that fuses with cell membranes.
Q & A
How does a virus enter and replicate within a human cell?
-A virus attaches to a human cell using its spikes, enters the cell, and uses the host cell’s machinery to replicate, producing viral proteins and genetic material. These are assembled into new viral particles, which are released as the host cell dies.
How does the immune system recognize an infected cell?
-Infected cells display pieces of viral proteins on their surface, which act as viral antigens. These antigens are recognized by cytotoxic T-cells, activating the immune system.
What role do dendritic cells play in the immune response?
-Dendritic cells, as professional antigen-presenting cells, patrol body tissues and capture viral antigens. They then travel to lymph nodes to present these antigens to helper T-cells, aiding in the immune response.
What are the two types of immunity triggered by viral antigens?
-Viral antigens trigger two types of immunity: cell-mediated immunity and antibody-mediated immunity.
How do vaccines induce an immune response without causing disease?
-Vaccines deliver viral antigens to the body, triggering an immune response similar to natural infection. This response includes the production of antibodies and other immune defenses, but without the disease symptoms.
Why might vaccines cause mild symptoms similar to an infection?
-As lymph nodes near the injection site start producing antibodies, they may become swollen and tender, which are signs of the vaccine working and can cause mild symptoms similar to infection.
What is the difference between attenuated and inactivated vaccines?
-Attenuated vaccines contain weakened viruses that can cause disease in people with compromised immune systems. Inactivated vaccines, such as Sinovac and Covaxin, use dead viruses and only induce antibody-mediated immunity.
What are subunit vaccines, and how do they work?
-Subunit vaccines contain only parts of the virus, usually a spike protein. They cannot cause disease but may not always trigger a strong immune response, so adjuvants are added to stimulate the immune system.
How do DNA and mRNA vaccines differ in their mechanism of action?
-DNA vaccines deliver viral DNA into the cell’s nucleus, where it is transcribed into mRNA and then translated into viral protein. mRNA vaccines, such as Pfizer and Moderna, deliver mRNA directly into the cytoplasm to produce viral proteins without entering the nucleus.
Why are non-human adenoviruses used in viral vector vaccines?
-Non-human adenoviruses are used because many people may have immunity to human adenoviruses, which could destroy the viral vector before it can deliver the DNA, reducing the vaccine’s effectiveness.
Outlines
🦠 Viral Infection and Immune Response Activation
The paragraph describes the process of how a virus infects human cells. The virus uses its spikes to enter the cell and hijacks the host cell's machinery to replicate itself, producing viral proteins and genetic material. As infected cells die, new viral particles are released, further infecting more cells. The infected cells alert the immune system by presenting viral antigens to immune cells, specifically cytotoxic T-cells. Professional antigen-presenting cells, like dendritic cells, also capture viral debris and transport it to lymph nodes where helper T-cells and B-cells are activated. These cells work together to mount both cell-mediated and antibody-mediated immune responses. The process takes time, during which the person experiences symptoms.
💉 Vaccines and Their Mechanisms
Vaccines trigger an immune response similar to a natural infection by delivering viral antigens without causing the disease. The immune response may sometimes cause mild symptoms as the body starts producing antibodies. Traditional vaccines contain weakened or inactivated viruses, but they require rigorous safety testing as attenuated vaccines may cause disease in immunocompromised people. Inactivated vaccines mainly induce antibody-mediated immunity. Subunit vaccines only use parts of the virus, like spike proteins, and usually need adjuvants to boost the immune response. Nucleic acid vaccines deliver genetic instructions for creating viral antigens, with DNA vaccines introducing viral DNA to the cell's nucleus and mRNA vaccines delivering mRNA into the cytoplasm to produce viral proteins.
Mindmap
Keywords
💡Viral infection
💡Antigen-presenting cells
💡Cytotoxic T-cells
💡Helper T-cells
💡B-cells
💡Antibody-mediated immunity
💡Cell-mediated immunity
💡Vaccines
💡mRNA vaccines
💡Subunit vaccines
Highlights
Viruses attach to human cells using their spike proteins to initiate infection.
Once inside the cell, viruses hijack the host's machinery to replicate and produce viral particles.
Infected cells present viral antigens to cytotoxic T-cells, activating the immune response.
Dendritic cells act as professional antigen-presenting cells by collecting viral debris and presenting it to helper T-cells.
The immune system mounts both cell-mediated and antibody-mediated immunity to target the viral antigen.
Vaccines deliver viral antigens to trigger immune responses without causing the disease.
Some vaccines, like inactivated ones, only induce antibody-mediated immunity and require extensive safety testing.
Subunit vaccines contain parts of the virus, such as the spike protein, and often require adjuvants to enhance the immune response.
Nucleic acid vaccines use genetic material, such as DNA or mRNA, to make viral proteins and trigger an immune response.
DNA vaccines deliver viral DNA into the cell nucleus, where it is transcribed into mRNA and then into viral proteins.
mRNA vaccines introduce mRNA into the cytoplasm, where it is translated into viral proteins, without integrating into the human genome.
Viral-vector vaccines use a harmless virus, such as a modified adenovirus, to deliver viral DNA, as seen with Sputnik V and Johnson & Johnson.
Non-human adenoviruses are often used in viral-vector vaccines to avoid pre-existing immunity in humans.
Concerns about DNA vaccines potentially integrating into the human genome have been largely dispelled by animal studies.
mRNA vaccines, like Pfizer and Moderna, are less likely to integrate into the human genome compared to DNA vaccines.
Transcripts
During a viral infection, the virus attaches itself to a human cell using its spikes.
Following entry to the cell, it uses the host cell’s machinery to replicate,
producing viral proteins and genetic material.
These are then assembled into new viral particles, which are released as the host cell dies.
New viral particles again infect more cells, destroying body tissues, producing symptoms.
Infected cells alert the immune system by displaying pieces of viral proteins
on their surface. By doing so, infected cells are said to present the viral antigen
to certain immune cells, namely, cytotoxic T-cells, and thus, activate them.
At the same time, debris of dead cells and viral particles themselves are picked up by so-called
professional antigen-presenting cells, of which dendritic cells are most effective.
Dendritic cells patrol body tissues, continuously sampling their environment for intruders. After
capturing the antigen, dendritic cells quickly leave the tissue for the nearest lymph node,
where they present the antigen to another group of immune cells, known as helper T-cells. Viral
particles also activate B-cells in lymph nodes. These groups of immune cells work together to
mount 2 types of immunity specific to the viral antigen: cell-mediated immunity and
antibody-mediated immunity. The process, however, may take up to a couple of weeks,
during which time the person is sick and the virus will have destroyed a vast number of cells.
Vaccines deliver viral antigens to trigger immune responses without causing the disease. The
events of a vaccine-induced immune response are similar to that induced by a natural infection,
although some types of vaccines may induce only antibody-mediated immunity and may therefore be
less effective. The immune process can sometimes produce symptoms similar to a mild infection,
even though there is none. As the lymph nodes near the injection site start producing antibodies,
they may become swollen and tender for a few days. These are signs that the vaccine is working.
Many existing vaccines contain a weakened or an inactivated virus.
Because the whole virus is used, these vaccines require extensive safety testing.
Attenuated vaccines may still cause disease in people with compromised
immune systems. Inactivated vaccines (Sinovac, Covaxin) only induce antibody-mediated immunity.
Subunit vaccines contain only part of the virus, usually a spike protein (EpiVacCorona). These
vaccines cannot cause disease, but they may not be seen as a threat to the immune system,
and therefore may not elicit the desired immune response.
For this reason, certain substances, called adjuvants, are usually added to stimulate the
antigen-presenting cells to pick up the vaccine. A subunit vaccine may also consist of empty virus
shells, without genetic material. Having a typical size and shape of a pathogen, these
vaccines may not require adjuvants to be perceived as danger, but they can be difficult to produce.
Nucleic acid vaccines contain genetic information for making the viral antigen, instead of the
antigen itself. DNA vaccines introduce viral DNA into the cell’s nucleus, where it is transcribed
into mRNA. The mRNA is translated into viral spike protein in the cytoplasm.
The protein is then displayed on the cell surface, just like with other types of vaccines.
Naked DNA vaccines (Inovio) require a special delivery method to reach the cell’s nucleus.
Alternatively, a harmless, unrelated virus may be used as a vehicle to deliver the DNA. In this
case, the vaccine is also known as viral-vector vaccine (Sputnik V; Johnson & Johnson’s). For
example, the Oxford-AstraZeneca Covid-19 vaccine uses a chimpanzee adenovirus as a vector.
The adenoviral genome is modified to remove viral genes, and the coronavirus spike gene
is added. This way, the viral vector cannot replicate or cause disease, but it acts as
a vehicle to deliver the DNA. The reason a non-human adenovirus is used is because most
people may have been exposed to human adenovirus and have immunity against it. The immunity could
destroy the vehicle before it can deliver the DNA and thus blunt the vaccine’s effectiveness.
DNA vaccines have raised concerns about the possibility of viral DNA integration into human
genome. However, studies in animal models have shown that integration frequency is well below the
frequency of natural, spontaneous gene mutations. mRNA vaccines (Pfizer, Moderna) introduce
mRNA that contains information for making the viral protein. mRNA molecules are delivered
within a lipid covering that will fuse with the cell membrane. Once inside the cytoplasm,
the mRNA is translated into viral antigen, which is then displayed on the cell surface.
Unlike DNA vaccines, mRNA vaccines are extremely unlikely to integrate into human genome,
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