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Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

author:Food and heart

On the prosperous Earth, there are about 8.7 million species of various sizes, shapes and lifestyles. There are large life such as blue whales, elephants and humans (the size is measured in meters),

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

There are also tiny or semi-living organisms such as chlamydia and viruses (size in nanometers, 1 meter = 100 million nanometers). Humans and animals feed on different types of animals and plants, and have survived and reproduced on the earth for generations; Chlamydia and viruses replicate and amplify themselves by infecting the host.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

In the process of life, extremely small viruses are almost "pervasive", and it is inevitable for human beings to encounter with viruses and fall into "encounter battles" with viruses.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

For this kind of guy, which is far from visible to ordinary microscopes, humans certainly can't fight it with tools or weapons. However, evolution has given humans a resilient immune system to strike a balance that allows humans to survive the fight against various pathogenic microorganisms such as viruses, germs and parasites.

Modern scientific research methods allow us to "enter" the microscopic world to understand and even "witness" this process, and the war between the human immune system and the virus is tantamount to a wonderful and thrilling science fiction war.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The influenza virus is one of the most common respiratory viruses that people encounter,

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The global flu pandemic of 1918, which tilted the demographic balance sharply, was the H1N1 strain of influenza A.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

There are four main types of influenza viruses: A/A, B/B, C/C, and D/D. Influenza A and B viruses cause seasonal epidemics almost every winter and spring, influenza C viruses generally cause only mild symptoms, and influenza D viruses mainly infect cattle.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

Since influenza viruses carry 2 unique proteins on their surface: thrombin (abbreviated H) and neuraminidase (N), humans have named influenza virus strains H+ number/N+ number. The main viruses that have circulated in humans in recent years are H1N1 and H3N2.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The global migration of migratory birds and modern large-scale livestock breeding will facilitate the transmission and mutation of viruses between animals, and influenza viruses are constantly evolving as animal-to-animal, animal-to-human, and human-to-human contact increases. Some viruses that originally could only infect birds and some viruses that originally only infected pigs acquired the ability to infect across species through genetic mutations, which may be interspersed and cross-infected in different hosts, causing large-scale epidemics, which are also the avian influenza and swine flu (chicken fever and swine fever) often reported in the news.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The influenza A virus mainly invades cells by binding to sialic acid receptors on the surface of human cells, and then transforms infected cells into "virus factories", releases them after replicating the virus in large quantities, and further infects other cells to establish more "virus factories".

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The process of replication of the new coronavirus infection is similar to that of the A virus, except in the receptor, which infects cells mainly by binding to ACE2 (angiotensintransferase 2) on the cell surface.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

Since sialic acid receptors are mainly distributed in the respiratory tract of humans and animals, influenza viruses mainly cause diseases by infecting respiratory epithelial cells with the help of sialic acid receptors.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The new coronavirus is different with the help of ACE2 receptors. ACE2 is also a key enzyme in the human renin-angiotensin system, which is widely distributed in many organs, so the damage caused by the new coronavirus infection is not only the upper and lower respiratory tract, but even more organs of the human body, which may bring more serious harm.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

No matter how menacing the virus is in the world, the body's autoimmune system will never sit still. In places that are invisible to our naked eyes, after the virus arrives, the immune cells in the body will fight for us with all their might.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The immune system mainly fights viral invasion through two types of reactions: innate immune response and specific immune response.

The innate immune response is non-specific, targeting all pathogenic microorganisms, which can fight both influenza A virus and new coronavirus. In the respiratory tract, the most important link in antiviral innate immunity is the type I interferon (IFN) response. In fact, interferon is also named precisely because it can interfere with viral replication.

Three types of interferons have been identified. Type I interferons mainly include 14 α isoforms, multiple β isotypes, IFN-ε, IFN-κ, and IFN-ω, sometimes abbreviated as IFNα/β. Type II interferons are mainly IFN-γ, and type III interferon jewelry includes 4 IFN-lambda subtypes.

Almost all cells in the human body produce IFN-β, but only certain cells, such as antigen-presenting cells, produce IFN-α. When the pattern recognition receptor in the cell recognizes a foreign nucleic acid signal (such as the RNA of influenza A virus or the RNA of the new coronavirus) or a non-nucleic acid pathogen signal, it causes IFN-α/β production through a series of signaling processes.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

Viral infection requires first breaking through the mucosal barrier and coming into contact with susceptible cells that carry specific receptors. After binding to the receptor, the virus can "hijack" human cells and replicate itself. After the specific receptor in the infected cell recognizes the viral nucleic acid, it will release information to activate the interferon signal and activate the type I interferon response.

Type I interferons induce the production of hundreds of interferon-stimulating genes (ISGs) that express proteins that block viral transcription, degradation of viral RNA, and inhibition of viral RNA translation and modification. For example, the ISG MX1 can help people fight the influenza A virus.

In addition to stopping viral replication in infected cells, type I interferons also alert infected cells to prepare for the virus (transition to an antiviral state).

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

Type I interferon response and innate immune cells interact with each other to prevent virus replication. The interferon response also activates antigen-presenting cells, transmitting viral signals to T cells, which in turn causes cytotoxicity of effector T cells and B cell differentiation to produce specific antibodies, thereby preventing the virus from continuing to infect.

In addition, type I interferons also help enhance immune memory and prepare humans for future viral challenges.

Whether it is influenza A virus infection or new coronavirus infection, when the body quickly initiates an effective interferon response, the body is often asymptomatic or only slightly unwell.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

However, specific immunity is especially important when the innate immune response does not clear the virus in time.

Antigen-presenting cells (such as dendritic cells) transmit the recognized antigen information to T cells, promoting the differentiation of CD8+ T cells into cytotoxic T cells (effector T cells), thereby destroying infected cells; Promote the differentiation of CD4+ T cells into a variety of helper T cells and regulatory T cells, which in turn stimulates B cells to differentiate into antibody-producing plasma cells and secrete antibodies specifically against the virus, thereby neutralizing the virus.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The specific immune process caused by influenza A virus infection is similar to that caused by the new coronavirus, but the T cells, B cells, and antibodies produced are only directed against influenza A virus.

Although the scope of influenza A virus in the body is not as wide as the new coronavirus, when the immune system cannot clear the virus in time and the infection does not heal for a long time, the long-term immune response will not only damage the respiratory function of the lungs, but also damage the lung tissue together with the virus, at this time, both influenza A virus and new coronavirus infection may cause acute respiratory distress syndrome (ARDS), which is life-threatening.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

In ARDS, viral infection and excessive immune attack lead to alveolar epithelial damage, alveoli are blocked by edematous fluid rich in pro-inflammatory proteins (such as various cytokines), alveolar epithelium deposits a large amount of fiber and surfactant is inactivated, alveolar capillaries rupture, at this time the alveoli lose elasticity and cannot exchange oxygen/O2 and carbon dioxide/CO2, the patient's breathing is blocked, and body cells cannot obtain sufficient oxygen to maintain normal function.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

When the influenza virus or new coronavirus infection is blocked in the upper respiratory tract (nasal, pharynx, larynx), the infected person will only have mild symptoms, but if the virus cannot be eliminated when it penetrates deep into the alveoli, it will reduce respiratory function, thereby affecting the oxygen supply and energy supply of human cells, interfering with the energy supply of lungs and other non-respiratory organs. If the virus is not cleared in the lungs, severe illness or even death may occur.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

The figure below briefly summarizes the process of viral infection and human defense.

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

To become infected, the virus first needs to break through the mucosal barrier and come into contact with susceptible cells that carry specific receptors. After binding to the receptor, the virus can "hijack" human cells and replicate itself. After the specific receptor in the infected cell recognizes the viral nucleic acid, it will initiate interferon signaling and activate the type I interferon response.

Type I interferon response and innate immune cells act to stop the virus from replicating. The interferon response also activates antigen-presenting cells, transmitting viral signals to T cells, which in turn causes cytotoxicity of effector T cells and differentiation of B cells to produce specific antibodies to destroy the virus.

Friends who have been paying attention to food and heart for a long time may wonder: Why didn't you mention the role of symbiotic flora? Aren't they important in anti-virus?

Picture and text to understand the human body's war with influenza A and the new coronavirus 1: Type I interferon reaction is the key

Of course not! Human symbiotic microorganisms are a complex group. To be precise, symbiotic microorganisms are not only friends of humans, but also accomplices of viruses. In this battle between viruses and humans, both sides are looking for helpers! If you misunderstand and treat fever, cough, sneezing and other manifestations in this struggle, and use incorrect drugs, it is likely that the virus is indirectly helping its own immune system.

In addition, some symptoms in the antiviral campaign, such as fever and cough, if treated incorrectly, are equivalent to helping the virus.

In the next issue, Food & Heart will take you to understand other participants in the war between viruses and human immunity, so stay tuned!