The Story of Immunity

The rise of the pandemic has certainly put an interest in immunity in society. The once depending-upon-the-medicine-for-immunity society is now focusing on how to create an immune response against the smallest of the infection. Everyone is trying. But to do that, it is necessary to understand how the immune system works.

Know the story of how immunity makes it happen!

Human Immune System – a complex group of defense responses found in all vertebrates, including humans. That is the base of how humans repel or prevent themselves from infectious viruses or pathogens. Pathogens or viruses can rapidly evolve and adapt to an environment thereby avoiding detection from the immune system. If the immune system cannot detect it, then the body cannot fight against it. We, as humans have a very sophisticated defense mechanism which includes the ability to adapt to recognize pathogens more efficiently.

This defense system includes many biological structures and processes within an organism that protects against disease. In order to function properly, it first must detect a different variety of agents known as the pathogens, right from viruses, bacteria to parasites, and learn to distinguish between them and the healthy tissue. The immune system is then divided into two subsystems, the innate and the adaptive immune system. In order to function, both of these use humoral immunity and cell-mediated immunity.

A nonspecific protective mechanism i.e. the innate immune system repels all microorganisms equally, while the specific immune responses i.e. the adaptive or acquired immunity is tailored to a particular type of invader. Both systems work together to obstruct the organisms from entering and propagating within the body.

How do the two subsystems work?

The innate immunity:

Most of the organisms encountered every day are repelled before they cause any issues to the body. These potential pathogens, which include viruses, bacteria, fungi, protozoans, and worms, are quite diverse and vary with their capacity to cause harm. Therefore a nonspecific defense system that diverts all types of this varied microscopic horde equally is quite useful to an organism. The innate immune system provides this kind of nonspecific protection via several defense mechanisms, which include physical barriers such as the skin, chemical barriers such as antimicrobial proteins that harm or destroy invaders, and cells that attack foreign cells and body cells harboring infectious agents.

The acquired immunity:

For centuries, a person who contracts a certain disease and survives is generally immune to it, which means he won’t catch it ever again. Unless the disease contracted is a variant of a virus. The Athenian general Thucydides said that during the era of the plague in Athens in the 5th century BCE, it was the devotion of those who already recovered from it, providing nursing to the sick and dying. It was clearly understood that no one ever caught the plague a second time. The same is applied to other diseases except for a few rare cases. The protection acquired by experiencing one of these infections is specific to that infection which is due to specific, acquired immunity, also called adaptive immunity.

There are a few other infectious diseases like the common cold that occur again and again. The reason such illnesses are caught again is that many different infectious agents produce similar symptoms. For example, according to the medical record, about 200 + viruses can cause a cluster of symptoms related to the common cold. Acquired immunity is relatable dependent on the specialized WBC’s known as the lymphocytes.

Evolution of the human immune system

This protective system we have acquired has evolved from simpler defense mechanisms, but the evolutionary twists and turns that lead a path to the development are not entirely clear. To reveal the path that the human immune system followed in its evolution, researchers have studied the defense responses of various living organisms. They also have examined the genes of the immune system proteins for hints and pieces of evidence to the genetic origins of immunity.

It is, with the help of positions of the animals in the tree of evolution, possible to trace back to the history of the immune system. It is, however, impossible to trace the evolution of immunity from the paleontological record. But since all animals exhibit a few general abilities to recognize self and to repel foreign bodies, it is possible to study the immune capacity of living animals.

As stated earlier, we as vertebrates have the most sophisticated immune system. Only in these organisms, it is possible to trace lymphocytes and immunoglobulins. The world’s most primitive living vertebrates, the jawless fish, do not have lymphoid tissue and their immune response is very weak. Moving forward, the fish with bones lacked lymph nodes but did contain clusters of lymphocytes in the gut that may be useful when required.

Further up the tree of evolution, terrestrial vertebrates – the mammals, the amphibians, etc. inherited a perfect immune system. The thymus, spleen, bone marrow, and lymph nodes were not only present but also made the IgM and IgG antibodies.

The evolution of the complement system (a group of proteins involved in immune responses) may have evolved faster than that of the immunoglobulin system. The fact that the complement system has gotten so well conserved and protected during evolution that has been of great biological value. The complement and immunoglobulin have also interacted throughout the evolution of the immune system in higher vertebrates.

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Published On: November 25th, 2020 / Categories: Articles /