Despite being surrounded by harmful microorganisms, toxins and various pathogens, humans manage to survive. All thanks to the immune system. The immune system has organs, tissues, cells and molecules that all work together to generate an immune response that protects us from microorganisms, removes toxins and destroys tumor cells. The immune response can identify a threat, mount an attack, eliminate a pathogen, and develop mechanisms to remember the offender in case you encounter it again.


Our immune system can be easily compared with the defense system of a country. It protects us from invaders and strengthens our power. Just as a country’s defence services have different divisions such as airforce and navy, similarly our immune system also has its own divisions. 


The main branches of the immune system are:

  • Innate Immune system
  • Adaptive immune system.

Innate Immune system

The innate immune response includes cells that are non specific, meaning that although they distinguish an invader from a human cell. They don’t distinguish one invader from another invader. The innate response is also feverishly fast – working within minutes to hours. The rise in temperature of your body, i.e fever happens due to the response of the innate immune system. But it has a negative point as well- it has no memory that associates with it. This means that the innate response will respond to the same pathogens in the exact same way no matter how many times it sees the pathogen. 


Adaptive Immune System

The adaptive immune system is highly specific for each invader. The cells of the adaptive immune response have receptors that differentiate one pathogens from another by their unique body arts called as the antigens. These receptors can differentiate between a  friendly bacteria and a potentially deadly one. The tradeoff is that the adaptive response relies on cell’s activation, so that they can differentiate and find the right kind of fighter cell to kill the pathogens. This takes time, maybe even weeks. But the biggest advantage of the adaptive immune system is its immunologic memory. So, the next time the same pathogens comes to attack our body, it kills it faster and much more easily.

Now let us look into the various immune system organs:


Hand, Rainbow, Light, Palm, Touch

Every country has a border, and there is an army there to protect it. This barrier of our immune system is our skin, which doesn’t allow any physical intruders to enter our body. Our skin contains a lot of proteins and peptides, both of which combat the microbes and germs which come in contact with it. Proteins such as lysozyme, calprotectin and defensine have antibacterial properties in them. They hinder the life process of the bacteria and don’t allow pathogens to come in. Other than this, the pH of our skin is also maintained in such a way that it doesn’t allow the growth of bacteria and pathogens in it. This is how our skin works as a physical barrier.


Our immune system has two major divisions in terms of organs
  • Primary Lymphoid Organs 
  • Secondary Lymphoid Organs

Primary Lymphoid Organs

Primary Lymphoid Organs are those organs, where immune cells develop. These include Bone Marrow and Thymus. The secondary lymphatic organs are the place where the defense cells do their actual work. These organs include the lymph nodes, the spleen, the tonsils and other specialized tissues in the mucous membranes of the bowel, for example.

Bone Marrow

Bone Marrow is a soft tissue, present in the longest bone of our body.Our bone marrow contains stem cells, which are responsible for producing blood cells of all kinds The major kind of dense cells are B-cells and T-cells. B- cells are synthesized in the bone marrow. Other than this, the B-cells also mature here. But on the other hand, T cells are only generated here, they don’t mature in the bone marrow. The mature B-cells further transports to the lymphatic organs through the blood for the further functions.



Thymus is an organ in between your two lungs. The thymus gland is the place where T-cells mature. The thymus serves a vital role in the training and development of T-lymphocytes or T cells, an extremely important type of white blood cell. T cells defend the body from potentially deadly pathogens such as bacteria, viruses, and fungi.

Secondary Lymphoid Organs

The secondary lymphoid organs are the spleen and the lymph nodes. They act as sites for maintaining the mature naive lymphocytes and are also the site where lymphocyte binding to antigen and hence their activation occurs. It contains the following organs:

  • Lymph nodes are bean-shape capsular structures and contain lymphocytes, macrophages, and dendritic cells. the lymph nodes provide an ideal micro environment for lymphocytes to encounter and respond to entering foreign antigens effectively.
  • The spleen is in the left abdominal cavity. Unlike the lymph nodes, the spleen has no lymphatic vessels but contains arteries and veins and is the major site for the clearance of antigens in the bloodstream.
  • Mucosa-associated lymphoid tissue or MALTs are always spread with the digestive, respiratory, and urogenital structures and are the major sites for initial contact with environment antigens. When foreign pathogens enter into the body, they must first attach to the mucosa which associates with the glycosylated proteins, and then they destroy the wall of mucosa.


The immune system is a vital organ in our body and helps to fight against various pathogens. It includes various organs which work together to complete the task.

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