Part 1. The immune system and respiration

Exercise 1. COVID-19 and respiratory infection (Maximum number of words in the answer: 1000 words) COVID-19 is an respiratory infection caused by the new coronavirus SARS-CoV-2. The disease was first detected in Wuhan, China in December 2019. The rapid worldwide spread of the virus in winter 2020 led the WHO on March 12, 2020 to declare the outbreak a pandemic. The virus causes everything from mild, barely noticeable symptoms to serious illness and death.

a) Explain the immunological response that occurs in the body when we get a viral infection. Which cells are activated and what causes this activation?

Ans:

Viral entry to the body is prevented first by the barrier of innate immunity, such as the IgA antibody on the mucus membranes and secretions. IgG, IgM, and IgA antibodies block the fusion of viral envelop with the host plasma membrane. Despite this, if a virus manages to get entry into the body, it is subjected to both the humoral immune response as well as the cell-mediated immune response. Both IgG and IgM antibodies enhance the phagocytosis of viral particles by the immune cells by Opsonization and in the company of the complement system leading to what is called the membrane attack complex. IgM antibodies in particular agglutinate viral particles.

Further, the PAMP (pattern associated molecular patterns) in the virus that is endosomal RNA in the Sars virus is recognized by the immune cells by pattern recognition receptors on the immune cells. This induces the formation of Type I Interferons in the infected cells, particularly the IFNλ through T helper cells (TH) and Cytotoxic T cells (TC). This inhibits the replication of viral particles in the adjacent cells. Also, the CTL or cytotoxic T cells directly kill viral particles. Apart from the above mechanisms, the Natural Killer cells and Macrophages kill virus particles by what is called 'Antibody-dependent cell-mediated cytotoxicity’ (ADCC).

b) Explain why COVID-19 has become a pandemic, while a regular seasonal flu has no such consequences.

Ans:

COVID-19 has become a pandemic due to its ability to spread faster. It is highly infectious with a vast majority of asymptomatic patients. Hence, a patient or a physician had already spread the infection before being diagnosed or the appearance of any symptom. Normal influenza viruses contain Haemagglutinin protein on the envelope that helps in binding to the host cell surface by binding to the sialic acid residues. However, SARS-CoV2 also contains a protein called 'Haemagglutinin esterase' that gives added armory to attach the host cell membrane's sialic acid residues. Also, the S proteins present in the spikes of the coronavirus provided further help in receptor (ACE2) recognition (by S1) and fusion to the host cell membrane (by S2). Thus the coronaviruses are highly infectious as compared to the normal influenza viruses.
Scientists around the world are now working hard to develop a vaccine against the new virus, but at best, such a vaccine will probably not be ready until about 12-18 months.

c) Explain the principle of how a vaccine protects an individual against disease and a population against the spread of infection.

Ans:

The adaptive immune response of human beings has the property of 'memory'. When a pathogen first infects a human being, a primary immune response is initiated that is slow and less intense. However, during this immune response memory, B cells and memory T cells are produced. When the pathogen again infects the same person, the memory cells act early, and a secondary immune response is initiated that is fast and higher in intensity than the primary response. When an individual is vaccinated, then a primary immune response is initiated. When we give a booster dose, the secondary immune response is initiated. Hence, when the actual pathogen attacks the individual, the secondary immune response is initiated very early and in very high intensity. Therefore, the pathogen is cleared off faster before getting any chance to expand its population in the host and thus substantially reduce the probability of transfer from the host to the new individual.

d) If a vaccine does not succeed, will it be possible to obtain immunity in the population? Discuss briefly.

Ans:

Even if a vaccine is not successful in a population. The surviving individuals from the infection have immunity due to memory cells of the adaptive immunity. When the number of such individuals increases in a population we achieve what is called a ‘herd immunity’. Suppose that approximately 60% of the individuals in a population have already been infected and acquire adaptive immunity, then the probability of virus spreading to the unaffected individuals is reduced significantly and the spread is thus contained.

Good lung function is important for respiration and gas transport in the body.

e) Explain what happens to respiration and gas transport in the body when lung function becomes severely impaired.

Ans:

When the lung function is severely impaired the gaseous exchange is impaired, and thus the patient is unable to release CO2 and get O2. As a result, the carbonic acid increased in the blood, and we get a condition of acidosis.

Part 1. The immune system and respiration Exercise 1. COVID-19 and...