Context: Though not different from influenza viruses and other coronaviruses responsible for the common cold, COVID-19 has affected over 1.5 million globally and killed more than 100,000 people, showing the immune system has a predictable response.
How does the virus enter?
- The viral particles enter the body through the nose, eyes or mouth.
- Breathing carries some of these particles to the lower respiratory tract where the spike proteins of the coronavirus, acting like a key, lock into epithelial cells that line the respiratory tract as well as those in the air sacs in the lungs.
- Remains undetected: SARS-CoV-2 is able to stay undetected longer than many flu or coronaviruses and its spike proteins are able to gain entry by unlocking the ACE2 protein on the lung cells.
- Viruses hijack the cell’s machinery, replicate and multiply and infect adjoining cells.
How does the immune system respond to a coronavirus attack?
- Since COVID-19 is not different from influenza virus and therefore the immune system has predictable responses.
- It is the degree to which this response is tolerated by the body that determines mortality rates.
- Viruses too have a tell-tale signature on their surface called antigens and spotting these is what kicks the immune system into action by producing antibodies.
- Activating the immune system: The signals they generate trigger another class of chemicals — cytokines and chemokines — and they alert the immune system to send an array of different kinds of cells that specialise in destroying viral particles.
- These cytokines and chemokines trigger inflammation in the cells.
- In the nose and upper regions of the respiratory system, this inflammation produces mucus and a runny nose to trap viral particles and prevent their ingress.
- It also triggers sneezes to expel them.
- When the sinuses are inflamed the infected person gets a headache and the general stuffiness that is associated with a cold.
- When the hypothalamus gland is infected, it results in fever.
How SARS CoV2 is different?
- In the case of SARS CoV2, the virus seems better at penetrating deeper.
- The inflammation triggers a fluid build-up in the lungs. The fluids also contain the residue of a host of specialised cells - including T cells - that carpet bomb and damage many of the body’s own cells as well as the viral particles.
- It is in expelling this fluid that a dry cough, characteristic of the coronavirus infection, begins.
- As more air sacs are infected, the lungs find it harder to perform their core job of extracting oxygen from the air, and eventually, this aggravates breathlessness.
- Based on degree of infection: The inflammation and the fluid build-up can lead to pneumonia.
- A patient will require hospitalisation to treat the breathlessness and ventilator support to artificially provide oxygen if the condition worsens.
- Damaging the vital organs: Massive levels of cytokines can cause extensive lung damage and a condition called Acute Respiratory Distress Syndrome. The unsustainable cytokine storm can cause organ damage far beyond the lungs and spread to the kidneys as well as the heart.
- In case of acute infection: It will lead to a depletion of the frontline white blood corpuscles tasked with fighting the infection and making the body vulnerable to other secondary infections, which may lead to death.
Immune system response:
- Weak immune system: those with existing conditions such as diabetes and cardiovascular disease, already have an inherent malfunctioning in the immune system.
- The reaction of the body in trying to combat the virus ends up being suicidal.
- Hydroxychloroquine or anti-HIV drugs, deployed to treat serious COVID-19 infection work in some way to moderate the immune-system’s aggressive defence.
Men are twice more likely than women to succumb to a COVID-19 infection:
- Women, on average, have a better-regulated immune response than men in pathogenic infections.
- Estrogen is said to be an immune-system modulator and the ability to deal with a pregnancy - which also begins as a foreign body growing within - primes women to better deal with infections.
- Not very clear: so far, there have been few deaths reported in children from COVID-19. Given that children’s immunity systems are still maturing and learning to adapt to a galaxy of infectious agents.
Image Source: Everyday health