Specific Immunity of the Human Defense System

Written By: Farkhunda

Immunity is the ability of multicellular organisms to recognize and destroy any foreign microorganism invading the cells. The human defense system has two types of immunity: non-specific immunity and specific immunity. Non- specific immunity is a physical barrier that prevents any pathogens (any microorganism that causes disease) from entering the body, such as phagocytosis (white blood cells), skin, and mucous membranes. Specific immunity, on the other hand, is the production of specific antibodies against particular pathogens.

The process of specific immunity

Specific immunity starts stimulating a response against any microorganism which passes through the physical barrier. An antigen (any organism foreign to the body such as bacteria and viruses) will be engulfed by phagocytic white blood cells at the moment of entering macrophage cells. The phagocytic white blood cell destroys the antigen and presents fragments of antigens on its membrane surface. These fragments are then shown to lymphocytic white blood cells, the T-helper cells (a type of thymus white blood cells), which have the right shape of binding sites for the fragments of the antigen. These antigen fragments are attached to the binding sites of the T-helper cell. Following that, the T-helper cell presents the antigen fragments to another lymphocyte, the B cells, which have binding sites too. When the fragments are attached to the B cells, the B cell starts replicating itself. Some of these replicated B cells become plasma cells that release antibodies to the specific antigen. The other replicated B cells would make memory B cells, which retain information about the pathogen for future immunity. The memory B cells do not act against the pathogens and only circulate in the body unless the same antigen enters the body. The next time when the same pathogen infects the body, the memory B cells release antibodies without going through the whole process again.

What are antibiotics?

Sometimes when the specific immunity is unable to destroy pathogens such as bacteria, antibiotics can be used instead. Antibiotics are antibacterial chemicals that kill or inhibit bacterial growth in the body by targeting the metabolic pathway of prokaryotes (unicellular organisms). These chemicals are made of the substances that can damage the metabolism of the prokaryotic cell without causing any damage to the eukaryotic cells (multicellular organisms). The pathways attacked by the antibiotics include bacterial DNA replication, transcription, translation, ribosomes, and cell walls.

However, antibiotics cannot be used to treat viral infections because viruses are not alive and do not have metabolic pathways. Once a virus enters a living organism, it gets activated. Thus, viruses cannot be treated with antibiotics because the host cells would also be affected by the antibiotic. Instead, viruses are treated by antiviral drugs and antiviral vaccines which do not destroy the virus but inhibit its growth. Vaccines do not work in a similar way as antibiotics, which destroy the metabolic pathways of the bacteria, but the vaccines themselves are viruses. Antiviral vaccines contain a weak form of the virus and antigens which triggers the production of the antibodies against that specific antigen through the specific immunity. The next time a virus enters the body, the memory B cell recognizes the virus and attacks it immediately. Sometimes vaccines can cause disease in people with vulnerable immune systems because their immune system is not strong enough to even fight the weak form of the pathogen (vaccines are made of weak living pathogens). Sometimes vaccines can cause diseases in people with vulnerable immune systems because their immune system is not strong enough to fight the living pathogen in vaccines (vaccines are made of weak living pathogens).

Types of vaccines

Not all vaccines are the same. There are different types, which include:

Live-attenuated Vaccines: This type of vaccine uses a living and weak form of the virus which will be injected into the body. Since the pathogen is weak, it cannot cause any disease but the body still produces antibodies against it such as vaccines for measles, mumps, chickenpox, influenza, and some others.

Inactivated vaccine: This vaccine is made of dead pathogens, killed by chemicals and heat. Inactivated vaccines do not provide a strong immunity against the pathogen, but the specific immune cells can still learn from it to prevent future risks from the same pathogen. Examples include polio, hepatitis A, and rabies.

Subunit or conjugate vaccines: This type of vaccine uses specific parts of the pathogen such as the capsid (a protein that covers the genetic material of the virus), protein, and sugar. As this vaccine targets particular parts of the pathogen, it provides very strong immunity against the pathogen. Examples of conjugate vaccines include vaccines for Hepatitis B, Shingles, whooping cough, and others.

Toxoid vaccines: This vaccine is made of the toxins of the pathogen instead of the whole pathogen, namely the vaccine for tetanus, diphtheria, and more.

To conclude, the human defense system is highly specialized in triggering different responses to a specific pathogen. However, sometimes this system becomes incapable of destroying the pathogen. Instead, the body will need extra chemicals to help it, such as antibacterial and antiviral medicines. Producing an antibacterial medicine is not difficult, but producing antiviral medicines is time-consuming because viruses are not alive. The difficulty of making antiviral medicine can be observed these days because of the Coronavirus pandemic.

Edited By: Happy

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“How Vaccines Work.” PublicHealth.org, PublicHealth.org, 22 Nov. 2019, www.publichealth.org/public-awareness/understanding-vaccines/vaccines-work/. Accessed 29 Jul. 2020

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