Immune System Innate vs. Adaptive Immunity

The immune system is our body’s internal defense system comprising many biological processes inside our body that protect us against germs and disease. For the defense system to function properly, an immune system must detect a wide variety of external agents, called pathogens, from parasitic worms to viruses (such as coronavirus). It also has to differentiate them from our own healthy tissues.

The immune system is a critical yet complex structure within the body which is diffused through most of the tissues of the body. It consists of lymphocytes, which are responsible for the production and secretion of antibodies. The unique characteristic of the immune system is the complex operation through pattern recognition, and its role is to patrol the body and guard its identity against foreign invaders. The mission of the immune system is simple: identify foreign invaders and kill.  

The immune system consists of a various defense mechanism which can be divided into two main types: non-specific and antigen-specific. The non-specific defense system includes the skin and mucous membranes, phagocytic cells, mucus, cilia, lysozymes, and other humoral factors. This defense system is present from birth in an individual and is part of the innate immunity, which is not influenced by prior contact with any infectious agent. Antigen-specific defense system includes B-lymphocytes and T-lymphocytes, which are adaptive and acquired during the lifetime of an individual by specific reactions induced by exposure to infectious agents.

The immune system of the body is regulated primarily by three prime systems, which are the lymphatic system, bone marrow, and thymus. The lymphatic system is an arrangement of lymph nodes and vessels in the body, which comprises of a clear fluid known as Lymph. The Lymph contains immune system cells, tissue fluid, and waste products. The Lymph nodes in the system are small, bean-shaped bodies of the immune system cells that are interconnected by lymphatic vessels. These lymph nodes contain white blood cells that trap viruses, bacteria, and other invaders, including cancer cells. Secondary organs that also aid the immune system in this defense mechanism are the spleen, tonsils, skin, and liver. These organs are responsible for the formation of white blood cells and leukocytes.[1,2,3]

What is the Immune System?

 There are two central cells which are responsible for the immune response in the body: white blood cells and lymphocytes. White blood cells originate from the bone marrow, while the lymphocytes originate from the lymphatic system. White blood cells comprise of macrophages, neutrophils, dendritic cells, eosinophils, basophils, and natural killer cells. These cells are part of the innate (natural) immunity. Lymphocytes are mainly of two types; B-lymphocytes and T-lymphocytes, which are responsible for the adaptive/acquired immunity. Whenever a foreign body enters the body, it is first encountered by the natural immune system, which involves the white blood cells. These cells try to eliminate the foreign cells either by phagocytosis (engulfing the foreign cell and dissolving it with the help of lysozymes) and chemical lysis. If the white blood cells are unable to fight and eliminate the alien invaders, they signal the lymphocytes, which are responsible for the secretion of antibodies that are targeted against the foreign invaders. 

Acquired immunity is characterized by higher specificity and slower speed than what our natural immune response does. Lymphocytes have receptor sites on cell surfaces. The receptor on each cell fits with a unique small molecular shape, known as antigen, on a given invader. It, therefore, responds to a unique kind of invader, like one key working with one lock only. When these are activated, these antigen-specific cells divide to create a larger population of cells. These cells are with the same antigen specificity in a biological process known as clonal proliferation or a proliferative response. This process is efficient in creating the number of cells that have to be supported on a daily basis. However, it creates a delay of up to several days before a full defense can be mounted. During this critical time, the body must rely on natural immunity to contain the infection.

The functions of each type of lymphocytes are different. As per a study, the distinct role of each kind of lymphocytes can be seen as follows:

⮚     B-lymphocytes

These B cells are responsible for the production of soluble proteins called antibodies that are secreted in response to specific antigens. Each B cell produces a specific antibody for the particular foreign antigen. For example, antibodies produced for bacteria causing pneumonia would be different from antibodies produced for a common cold virus. They are also responsible for opsonization, in which a coating of antibody increases the effectiveness of natural immunity. There are five types of antibodies:

1. Immunoglobulin G (IgG) – marks microbes so other cells can recognize and deal with them.

2. Immunoglobulin M (IgM) – is an expert at killing bacteria.

3. Immunoglobulin A (IgA) – present in fluids, such as tears and saliva, where it protects gateways into the body.

4. Immunoglobulin E (IgE) – protects against parasites and is also to blame for allergies.

5. Immunoglobulin D (IgD) – stays bound to B lymphocytes, helping them to start the immune response.

⮚     T-lymphocytes

The T cells get matured in the thymus where they are differentiated into different types of T cells which are:

1. Helper T cells – Their primary function is to produce and secrete cytokines that direct and amplify the rest of the immune response.

2. Killer T cells – As their name suggests, these cells recognize the antigen expressed by cells that are infected by the foreign cells or otherwise compromised and destroy those cells. [4,5,6]

Immunity Types

Immunity is defined as the ability of the immune system to fight against any disease, infection, or unwanted foreign invader. As per a research study, immunity is of two types:

1. Innate immunity:

The innate immunity type provides the first level of defense against infection whose response time is within minutes. It is not specific to any particular foreign cell, has no memory, and does not provide long-lasting immunity. It consists of natural barriers, which are the skin, mucous membrane, etc. and the white blood cells which are neutrophils, macrophages, natural killer cells, etc. Humans, by birth, are equipped with this type of immunity.

2. Adaptive / Acquired immunity:

This type of immunity is developed by the individual through his lifetime. The immune response exhibited by the immune system is highly specific against foreign infection. The response time of this immune system is rather slow and may take up to weeks but is highly effective against the foreign invasion. Following exposure to an external infection, there is an initial effector response that eliminates or neutralizes a pathogen. Later re-exposure to the same foreign organism induces a memory response with a more rapid immune reaction that eliminates the pathogen and prevents disease. Hence, it provides long-lasting immunity to the individual. Vaccination, which is provided to infants in their early days, helps them develop acquired immunity against various harmful infections and disease-causing bacteria and viruses. It helps them protect themselves from any future encounter with the bacteria or virus. [7,8]

The immune system is incredibly well-structured in the body, which is vital for our survival. Appropriate measures should be taken to keep the immune system of the body healthy. The effective performance of the immune system is necessary for our survival. Adequate sleep, yoga, exercise, meditation, nutrition, etc. are essential for improving and boosting immunity. These factors should be included in the day to day routine to have healthy immunity.