Media speculations regarding immunity to COVID-19 for those who have already experienced the disease have become quite common. Theoretically, if a large proportion of the country had encountered the virus, the rest of the population would remain safe given that there would not be a pathway of transmission. This type of immunity involves antibodies and memory cells. Memory cells are effector cells that differentiate differently than other immune cells when foreign organisms are encountered. Once there is a re-infection, they remember the structure of the foreign microorganism they have faced previously and produce immune responses more rapidly than the initial encounter. Although it is too soon to say whether people who already had the coronavirus have gained immunity to COVID-19, since the research is still ongoing, there are many other aspects in our body where memory cells are involved in producing rapid immune responses.  

The production of memory cells can be a curse. This is the case for allergic reactions. In the first encounter, allergens can be ingested, inhaled, or enter dermally into the human body. Once the first encounter happens, the exposed person produces specific antibodies called IgE antibodies. This happens without initiating an allergic reaction initially. But once the allergens are re-encountered there are many repercussions that may make that individual very ill. This is because during the first encounter some immune cells have differentiated into memory cells and when stimulated once again by the same allergen, they recognize the structure and therefore can produce an immune response rapidly. In the case of allergies, memory cells are to blame for unwanted reactions; however, sometimes memory cells can be vital in producing effective immune responses and gaining immunity to certain viral and bacterial infections.

Vaccinations rely on the immune system to produce memory cells. The role of vaccinations is to imitate infections. Vaccines include dead or weakened pathogens that will still initiate the production of T-cells and B-cells. Some of these cells will become memory cells so that when a real pathogen is encountered once again, these memory cells can recognize and act quickly to prevent dangerous infections and symptoms.

The smallpox vaccine is known as the first-ever home-made immunization. In 1796, Dr. Edward Jenner observed that milkmaids exposed to cowpox were not experiencing smallpox symptoms. So, by hypothesizing that cowpox allowed people to gain immunity to smallpox, he inoculated a young child with cowpox scabs and exposed him to smallpox. He discovered that the kid had gained immunity to smallpox, and started inoculating more people. This process of immunization for smallpox was possible due to the viral structural similarity between smallpox and cowpox. The memory cells that were produced specifically to cowpox were able to create immune responses to smallpox due to this similarity. With the development of more advanced vaccines for smallpox over time, smallpox was eradicated by the 1980s. 

If this is the case, shouldn’t we have found a vaccine for every microorganism? Why haven’t we still found a cure to HIV/AIDS? This is because HIV mutates rapidly, quicker than we can produce a vaccine. The antibodies and memory cells that are produced by the first encounter cannot recognize the re-encountered virus because they have already mutated! Therefore, vaccine discovery strategies have been largely focused on identifying the conserved structures within the HIV virus; however, a cure for HIV/AIDS is yet to be found. Although not as rapidly mutating as HIV, Influenza, also known as the flu, is known to experience changes through antigenic drift and shift. This is why we receive a flu shot every year, to be immunized for the newly mutated virus.

Memory cells can be a burden and a blessing for the immune system and the human body. Memory B cells can be T or B lymphocytes that remain in the body long after the foreign substance has been encountered initially. Although they might be the reason for unwanted allergic reactions, they are also our body’s smart defense mechanism against previously encountered microbes. This is why it is vital that we support our immune system by maintaining a healthy lifestyle and receive vaccinations when necessary.

References:

Belongia, E. and Naleway, A., 2003. Smallpox Vaccine: The Good, the Bad, and the Ugly. Clinical Medicine & Research, 1(2), pp.87-92.

Cdc.gov. 2020. [online] Available at: <https://www.cdc.gov/vaccines/hcp/conversations/downloads/vacsafe-understand-color-office.pdf> [Accessed 2 October 2020].

Centers for Disease Control and Prevention. 2020. How Flu Viruses Can Change. [online] Available at: <https://www.cdc.gov/flu/about/viruses/change.htm> [Accessed 2 October 2020].

Fliesler, N., 2020. Keeping Up With HIV Mutations. [online] Hms.harvard.edu. Available at: <https://hms.harvard.edu/news/keeping-hiv-mutations> [Accessed 2 October 2020].

Medicalxpress.com. 2020. COVID-19: Herd Immunity In Sweden Fails To Materialize. [online] Available at: <https://medicalxpress.com/news/2020-08-covid-herd-immunity-sweden-materialize.html>.

Medicalxpress.com. 2020. Immune Cells Hold Their Memory Of How To Respond To Allergens In A Surprising Way. [online] Available at: <https://medicalxpress.com/news/2018-02-immune-cells-memory-allergens.html> [Accessed 2 October 2020].

Writers, S., 2020. How Vaccines Work | Publichealth.Org. [online] PublicHealth.org. Available at: <https://www.publichealth.org/public-awareness/understanding-vaccines/vaccines-work/#:~:text=Inactivated%20Vaccines%3A%20For%20these%20vaccines,of%20it%20in%20the%20future.> [Accessed 2 October 2020].