We all despise seasonal flu—days spent in bed with a pounding headache, lethargy, fever, stuffy nose, coughing up coloured mucus (which you never expect to come out of you!), and the body's predicament between chills and sweating.
The only silver lining during the flu is being pampered and enjoying some comforting chicken soup. That is if you can taste it!
I remember being down with flu most of the time when I was eight and nine. In my bedroom loft, my parents had placed a box of non-stick cookware with a picture of a delicious 'Bindi ki sabzi,' or an Okra dish, along with other items.
This image taunted me of the bland meals offered during my days in bed. Alone in my bedroom, as I lay with heavy eyes, a parched and sore throat, weak and exhausted, I wondered if this was what life was all about!
Fortunately, years after, I could maintain perfect attendance at school. I was no longer susceptible to the clutches or, shall I say, the 'spikes' of the seasonal flu. It was only a few years later that I learned about the immune system.
Our immune system is complex, and complex mechanisms protect us from being vulnerable to disease-causing agents. These agents include viruses, bacteria, fungi, protozoans, and parasitic worms. However, let me restrict this blog post to the immune response against viruses.
Introducing the Influenza Virus: The Villain Behind Flu
From the above context, you must know by now that the discussion will include the influenza virus. But which influenza virus?
You should know that only specific influenza virus strains (variants) can infect humans. Particular strains infect only birds, while others infect mammals, such as swine or horses.
In this blog, I shall not provide an in-depth account of the structure of the virus as it is totally out of scope. However, I will be concise on it to help you appreciate your immune system.
Influenza A is generally responsible for human pandemics. So, I shall anoint it, the 'villain' of the story! What does the villain look like?
Meet Influenza: A Closer Look at This Microscopic Invader
As we have seen in movies, villains usually don the most bizarre costumes, long-dark hoods, capes, bold jewellery, spikes, etc. Similarly, the villain of this story, influenza A, is enveloped with 'spikes' all over.
The spikes are weapons comprised of Hemagglutinin and Neuraminidase. Within this envelope is the nucleocapsid, a protein layer that protects the genetic matter.
All villains have weaknesses that can destroy them. If this villain is targeted, the genetic material, eight single-stranded RNAs, is its greatest weakness!
The villain is also a remarkable 'con artist.' As a part of their game, these con artists change their identities. But how does influenza A do it? The villain alters the Hemagglutinin and Neuraminidase spikes protruding from its envelope. These changes can occur gradually or suddenly.
Now, who protects us from these con artists, a.k.a. villains?
Immune System: Body's Ultimate Defence System
Our complex immune system defends our body against the invasion of foreign particulate matter, including influenza A. Hence, the immune system has also been termed the defence system.
The first line of agents in the defence system is the macrophages and the neutrophils. A warning is raised the minute the villain is detected. The alarm alerts the other agents of the defence system, including the T cells and B cells*. These agents remain active in the villain's presence and produce memory cells.
How Does the Immune System's Defence Operation Unfold?
Remember, the eight-year-old me sick with flu in bed? I was a naive subject who hadn't encountered the villain before. The villain entered my body as I breathed in the aerosols where they were dormant.
The villain's weapon, Hemagglutinin, clasps the cell receptors and invades them. Once the villain proliferates inside, they swarm out, using Neuraminidase to slash open the infected cells.
Meanwhile, the first line of agents in the defence system quickly identify the Hemagglutinin spikes on the villain as foreign, thereby initiating the defence operation.
The activated T cells trigger B cell activation. The B cell defence system has two wings: the short-lived plasmablasts and the memory cells. Plasmablasts generate specialised weapons called 'antibodies.'
During the defence, antibodies increase in the body, preventing the villains from entering healthy cells. Simultaneously, the T killer cell wing kills the villain-infested cells. Thus, the agents, T and B cells, work together to neutralise the villain. The activated immune response to the villain is what we experience as 'flu symptoms.'
Battling the Flu: How Your Immune System Prevents Influenza Reinfection
The memory cell wing logs the revealed villain's identity into their 'villains' database.' When encountering familiar villains, the memory cell wing would recognise the villain and activate rapidly.
The powerful fighters producing a surge of antibodies would swiftly neutralise the invaders. Hence, saving us from that villain, influenza, once again!
Why Are Influenza Viruses Con Artists? Their Trickery and Immune Evasion
I would fail if I did not clarify why I termed influenza A the 'con artists.' In a constant game of deception, the villain changes its appearance, altering their antigens** and leaving the memory cell wing of the immune system bewildered.
These changes can leave the defenders unable to recognise the new identity of the villains, rendering their weapons less effective. The defence system flounders to keep up with these con artists, leaving us susceptible to reinfection.
A sudden, drastic transformation could lead to cross-species infections that unleash pandemics. However, this is a topic for another day.
We have an incredible defence system, don’t we? If you enjoyed this article and found it comprehensible, feel free to comment and share it on your social media!
References
Krammer, F. (2019). The human antibody response to influenza A virus infection and vaccination. Nature Reviews Immunology, 19(6), 383-397.
Punt, J., Stranford, S., Jones, P., & Owen, J. (2019). Kuby Immunology (6th ed.). W.H. Freeman and Company
Slifka, M. K., & Amanna, I. J. (2019). Role of multivalency and antigenic threshold in generating protective antibody responses. Frontiers in immunology, 10, 956.
*T and B cells originate in the bone marrow. However, the abbreviations T and B are Thymus and Bone marrow, where these cells mature.
**The molecule that activates the immune response is called the 'antigen.' Hence, Hemagglutinin is an antigen!
The weapons, or antibodies, are specific to the antigens. Any changes to the antigens render the antibodies useless.
I love your writing style. It made for an interesting read about Influenza.
This is such an interesting, important and informative article. Thanks for sharing.
Geat a rticle. Influenza is a dangerous virus!
From what I've heard, Influenza is a dangerous virus. Thanks a lot for educating all of us about it!