Development of the Immune System and Maturation of T-Lymphocytes

Components of the immune system

The immune system is a complex network of cells, organs, tissues and other substances that helps the body to fight against microorganisms. It consists of the lymph system, white blood cells, eosinophils, spleen, lymph nodes, basophils, mononuclear phagocytic cells, neutrophils, mast cells and bone marrow.

The immune function plays the role of immune surveillance, regulation and defence. The major components of the immune system are listed below. These cells work together to protect the body and defend against the invading cells.

T cell

The T and B lymphocytes are the two main cell types made in the bone marrow. It is commonly found in the lymph tissues and blood.

The development of T cells occurs in the thymus, and the differentiation for positive and negative selection occurs in the thymic environment.

The specific T cell markers like TCR, CD3, CD2, CD4 or CD8 development also occurs. The thymus is a multi-lobbed organ that is composed of medulla and cortical areas, which will be covered or surrounded by a capsule.

The T cell first enters the subcapsular cortical area, where they undergo proliferation for a period of time. After differentiation, they move to the medulla from the cortex. If the T cells do not undergo proper differentiation to become a mature T cell, they will die by apoptosis.

B cells

B cells are a type of white blood cells. These cells make antibodies that help fight infections. B cells make antibodies in response to antigen generators. The B cells play an important role in innate immunity.

The B cells produce antibodies that kill the antigens or the pathogens. These pathogens or microorganisms, when they enter the body, will cause disease. The B cells also tend to remember attacks, and when the same pathogen invades the body again, they eliminate them.

The B cells work together with other immune cells to fight bacteria, viruses and other pathogens. When the B cells are activated, they become plasma cells that produce antibodies.

The B cells are located in various places depending on their stage of development. For a foetus, the B cells are made in the liver and for adults, the B cells are made in the bone marrow. When the B cells mature, they travel to other parts of the lymphatic system, like the spleen and lymph nodes.  

Development of immune cells

The immune system works hard to keep you healthy and strong. The key role is to kill the germs and limit the extent of destruction that can cause to the body.

How do you know your immune system is working properly?

When the immune system works properly, it will kill the invading organism. It will also mobilise, attack and kill the organism. The body will tend to develop antibodies for the attacking pathogens, and it will also learn to defend itself from the invading germs.

In some cases, the doctor might prescribe some antibiotics to help the immune system fight better. However, the antibodies will only kill certain bacteria and are not effective against viruses.

Innate immunity

Innate immunity is the first to respond when an attack happens. The skin, eye’s cornea and mucous membrane are some of the examples of innate immunity. These organs, cells or tissues create a barrier and protect the body.

The first line of defence will protect against germs, parasites and other invading cells. Innate immunity is inherited and will be present from the day an individual is born.

When innate immunity recognises an attack, it gets into action. When the cells get to the site of infection, they surround and cover the invading cells. The invading cells will be killed by the process of phagocytosis.

Adaptive immunity

Adaptive immunity makes antibodies with innate immunity and kills the foreign bodies that invade the body. The antibodies will be developed by the B cells and get activated when an antigen activates the antibodies.

The antibodies will stay in the body, and after the first exposure, the immune system will recognise the invading foreign pathogen and defend the body against it. The adaptive immune system will change as the child grows, and the antibody will get activated when the system changes. Immunisation will also play a crucial role in adaptive immunity and protect them from invading organisms.

Immune decline with age

As an individual age, their immune system tends to decline. The immune system will experience various pathogen attacks, and they will get past the health and survival stage. So there is a higher chance of acute bacterial and viral infections.

According to NCBI, infectious diseases are the most common cause of death among elderly people in developed countries. Additionally, the immune response in elderly people can cause inflammation, leading to further suffering.

Likewise, the ageing immune system will fail to maintain full tolerance to self-antigen, which increases the incidence of autoimmune diseases. This can occur due to reduced white blood cells— called lymphopaenia. Lymphopaenia will lead to excess homeostatic lymphocyte proliferation and also a decrease in regulatory T cell function.

Evolution of the human immune system

The immunity of humans has evolved over the years. Memory cells have also evolved over the years to remember the pathogen attacks. The immune system changes and adapts over the years of an individual to function fully and also to establish a memory bank of pathogens over the years.

Every infection or pathogen will mould the immune system effectively and react to acute infections. It also adapts to pregnancy and other seasonal infections. In some cases, the immune system of aged people will resemble a newborn with reduced antimicrobial activity by neutrophils and macrophages.

Conclusion

The immune system is important for an organism to protect and fight the invading organism. The immune system identifies the self and non-self cells and kills the invading organism.

Additionally, the cells also tend to remember past attacks, and this will help to eliminate the invading cells at the first point of attack. In some cases, the immune system will weaken due to certain infections.

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