Watch | The immune system's response to a coronavirus attack

A video explainer of how your immune system responds to SARS-CoV-2

COVID-19 is not different from how influenza viruses attack the body. Therefore, the immune system has a predictable response to it .

A cascade of viral particles enters the body through the nose, eyes or mouth. Breathing carries some of these particles to the lower respiratory tract.

Here the spike proteins of the coronavirus, acting like a key, lock into epithelial cells. SARS-CoV-2 is able to stay undetected longer than many flu or coronaviruses.

Its spike proteins are able to gain entry by unlocking the ACE2 protein on the lung cells. Once in, they hijack the cell’s machinery, replicate and multiply and infect adjoining cells.

Viruses have a tell-tale signature on their surface called antigens. Spotting these is what kicks the immune system into action by producing antibodies.

The signals they generate trigger another class of chemicals — cytokines and chemokines. They alert the immune system to send an array of different kinds of cells that specialise in destroying viral particles.

However, these cytokines and chemokines trigger inflammation in the cells. In the case of SARS-CoV-2, the virus seems better at penetrating deeper.

The inflammation triggers a fluid build-up in the lungs. Apart from producing mucus and a runny nose to trap viral particles and prevent their ingress.

The fluids also contain the residue of a host of specialised cells — including T cells. These 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 airsacs are infected, the lungs find it harder to extract oxygen from the air. And eventually, this aggravates breathlessness.

The elderly already have an inherent malfunctioning in the immune system. Especially those with existing conditions such as diabetes and cardiovascular disease.

Mortality statistics globally suggest that men are twice more likely than women to succumb to a COVID-19 infection. Estrogen is said to be an immune-system modulator. The ability to deal with a pregnancy primes women to better deal with infections, say experts.