Our body's natural defence mechanism, the immune system, serves as a vital shield against external threats. Its primary function lies in discerning between what belongs to our body and what doesn't. By identifying and combating foreign entities like viruses, bacteria, fungi and parasites, the immune system safeguards our health.
The immune system stands as a vigilant guardian, dedicated to safeguarding our body from various external threats and diseases such as the flu, coronavirus, chickenpox, and the common cold, among others.
Remarkably, our immune system also stands as a formidable barrier against cancer cells, actively inhibiting tumors and thwarting the progression of cancer within our bodies. Delving deeper into this fascinating aspect, I'll soon dedicate a separate blog post to elucidate the intricate mechanisms through which our immune system combats cancer.
In this blog, we''ll explore how the immune system works, and the vital cells and organs that defend our body against diseases. My goal is to explain the immune system - in the easiest way possible.
The immune system comprises of immune cells, so let's start by understanding how and where immune cells are formed.
Primary Organs
The immune cells develop in primary organs like bone marrow and thymus. The bone marrow is like a factory where all blood cells are made - red blood cells, white blood cells and immune cells like T and B lymphocytes. In the bone marrow and thymus immune cells are shaped and readied for their roles in defending our body.
1) Bone Marrow - where it all begins :
The journey starts with pluripontent stem cells that are found in the bone marrow - infact the bone marrow is made up of these cells. These cells give rise to common myeloid progenitor cells and common lymphoid progenitor cells. The myeloid cells further differentiate into red blood cells and white blood cells. The white blood cells or granulocytes like neutrophils, basophils and eosinophils are considered essential as first line of defense. The myeloid cells also differentiate into monocytes and dendritic cells which play an important role in the immune system ( we shall explore this in the next blog ). Meanwhile lymphoid progenitor cells turn into Lymphocytes - known as T and B lymphocytes. In addition to lymphocytes, Lymphoid cells also produce Natural killer (NK) cells - and these 3 cells are the frontline fighters (most important cells of the immune system) against any infection and diseases. (See the pictorial represtenation below Fig.1 for better understanding)
2) Thymus - a bootcamp for training and prepping immune cells :
The T and B immune cells start their journey in the bone marrow, while B cells remain in the bone marrow for further development and maturation, the T cells travel to the thymus. The thymus, located near the heart, is like a training ground for T cells. It is active during our growing years (adolescence), and produces a special hormone called thymosin which is essential for T cell development. Inside the thymus T cells multiply and learn how to recognise different inavders. It is in thymus where T cells differentiate and develop special proteins on their surface like CD4 and CD8, which further helps them with their tasks. By the time we reach puberty the thymus will have trained enough T cells that can last us a lifetime.
Secondary Organs
Secondary organs of the immune system are the lymph nodes, spleen, peyer's patch and various mucousal membranes (MALTs & GALTs) in the body. It is in these specialised organs where the immune cells act on germs and other foreign substances i.e matured immune cells that are trained in primary organs enter the secondary organs where they are activated and do their actual job of fighting and killing germs and other foreign substances.
1) Lymph Node and Spleen - Act as immune checkpoint and helps identify microbes for immune cells to take action.
Once matured, immune cells move to lymph nodes and spleen waiting for their call to action. Lymph nodes are like check points scattered throughout the body, while the spleen acts as an active filter for our blood - by clearing out damaged red blood cells and stores important cells like platelets and white blood cells. In addition to this the spleen also helps in identifying microorganisms that might pose a threat to the body.
2) MALTs & GALTs : Immune hubs acting as a strong line of defense against pathogens
Besides the lymph node and spleen there are other immune hubs in the body known as mucosal assosiated lymphoid tissue also known as MALTs and gut associated lymphoid tissue also known as GALTs. MALTs are found in places with mucous membrane like the intestine and the mouth, while GALTs are found in gut and related organs. Both help defend against inavders trying to sneak in through these routes.
Now lets introduce you to the soldiers of our immune system - the innate immune cells and adaptive immune cells.
Innate cells - Granulocytes (neutorphils, basophils and eosinophils) are our first line of defense. Think of them as rapid response team, always on the lookout for trouble and always ready for action. Neutrophils for example are quick to act against bacteria and macrophages are like the clean up crew, gobbling up debris and sending alerts to other immune cells if things get out of control and serious (Fig.2)
Adaptive cells - Natural killer cells, T cells and B cells are like specialised fighters, when activated they unleash targeted attacks against inavders. T cells, for example go against pathogens directly, while B cells produce antibodies to tag them for destruction. These cells play an important role in fighting cancer, but there are other cells like dendritic cells that help coordinate the battle. They are like military generals who strategise and direct troops when at war.
The adaptive cells result in the most important immune process of the body which is called Adaptive Immunity - which can be further classified to Humoral immunity and Cellular Immunity.
Humoral Immunity :
Also known as antibody-mediated immunity, is orchestrated by a collaboration between B cells and helper T cells. When faced with specific antigen (foreign substance or protein), B cells transform into plasma B cells, armed with the ability to produce antibodies tailored to combat the invader. This aspect of immunity is particularly effective against pathogens circulating freely in the body. The antibodies generated by plasma B cells bind to antigens, rendering them harmless through neutralization or triggering process like lysis or phagocytosis (englufment of microbe or pathogen by the cell) , which dismantle or engulf the threat.
Cellular Immunity :
Cellular immunity operates within infected cells and relies on the prowess of T lymphocytes. When a pathogen infiltrates a cell, its antigens are presented on the cells's surface or by specialized antigen-presenting cells. Helper T cells come into play, releasing cytokines (chemicals that help the immune system function efficiently) that guide activated T cells to recognise and latch onto infected cell's antigen presenting complex. Once bound, the T cell morphs into a cytotoxic T cell, which launches an assault on the infected cell, causing it to undergo lysis, ultimately destroying the pathogen from within.
Conclusion :
In conclusion, our immune system stands as a testament to the marvels of human body, tirelessly defending us against a myriad of threats. From its inception in the bone marrow to the frontline warriors , every component works harmoniously to safeguard our health. It operates as an ever-ready boot camp, continuously preparing for battles we may face. Yet, amidst its ceaseless efforts, lies a symbiotic relationship - we are entrusted with the responsibility of nurturing and supporting it - Through proper nutrition, ample rest, sunlight exposure and regular exercise, we fortify our body’s defences, ensuring our immune system remains robust and resilient. As we navigate through life, let us not overlook the significance of this intricate defence mechanism. By honouring our bodies and prioritising our health, we honour the extraordinary effort of the immune system - a guardian working tirelessly to preserve our well-being.