Innate And Acquired Immunity

The immune system fights against germs and foreign substances on the skin, in the body’s tissues, and in bodily fluids such as blood. The overall ability of the host to fight the disease-causing organisms conferred by the immune system is called Immunity. The immune system can be broadly categorized into two types, the innate (Non-specific) immune system and the acquired (specialized) immune system. These two systems work closely together and take on different tasks.

Difference Between Innate and Adaptive Immunity

Innate Immunity

Innate Immunity is also known as General or Non-specific Immunity. It is a long-term non-specific immunity that is present in the organism by birth. 

• The Activation of the innate immune system results from an attack by any pathogen. Since it works in a generalized way regardless of the type of pathogen, that is also the main reason why it is called Non-specific immunity. 
• It provides a natural resistance component, such as salivary enzymes, natural killer cells, intact skin, and neutrophils, etc. 
• It provides a long-term immunization towards any pathogen by producing antibodies.

Innate Immunity is also called a first-line defense system, which includes various barriers that restrict the pathogen’s entry into the body. Following are the natural barriers that prevent the entry of pathogens. 

	Barrier	Explanation
1.	Physical barriers	The skin on our body is the main barrier that prevents the entry of micro-organisms. Mucus coating of the epithelium lining the respiratory, gastrointestinal,, and urogenital tracts also helps to trap the microbes and stop them from entering our body.
2.	Physiological barriers	Acids in the stomach, mouth, saliva and eye tears prevent microbial growth.
3.	Cellular barriers	Certain types of leukocytes (WBC) of our body, like polymorphonuclear leukocytes (PMNL-neutrophils) and monocytes and natural killers (kind of lymphocytes) in the blood as well as macrophages in tissue, can phagocytose and destroy microbes.
4.	Cytokine barriers	Virus-infected cells secrete proteins called interferons which protect non-infected cells from further viral infections.

Cells Involved in Innate Immunity

Following are the cells involved in Innate Immunity

S.No.	Cells	Role of Cells
1.	Dendritic Cells	They are the first-line worriers found in the tissues and perform the function of fighting with the microbes and sending signals to the other immune cells.
2.	Natural Killer Cells	They are involved in killing all those cells which got infected with the microbes.
3.	Macrophages	They have the ability to circulate in the blood and also to move into the tissue. They particularly produce cytokines which alert all the other immune cells.
4.	Mast Cells:	They are involved in the healing process and defense against infections.
5.	Neutrophils	They contain granules that help in killing any bacteria or pathogen.
6.	Eosinophils	They produce a toxic protein that is involved in skinning bacteria.
7.	Basophils	They produce a protein called histamine against multicellular parasites.
8.	Phagocytes	They circulate throughout the body and kill all foreign substances by engulfing them.

Acquired Immunity

Acquired immunity, also known as adaptive immunity, is the immunity gained over the life span by getting exposed to different pathogens throughout life.  

• It is a slow response as compared to innate immunity.
• It is specific to a particular antigen or pathogen and is mediated by various lymphocytes and antibodies.
• When an individual is exposed to a certain pathogen, a memory regarding that pathogen is created, and then again that pathogen attacks that individual at that time, the adaptive immune system has a memory to fight against that pathogen in the form of antibodies. 

Types of acquired that Immunity

S.No.	Type	Sub-type	Description
1.	Active Immunity	Natural	Antibodies are made after exposure to infection.
2.		Artificial	Antibodies made after getting a vaccination
3.	Passive Immunity	Artificial	Antibodies transmitted from mother to baby (e.g., via mother’s milk)
4.		Artificial	Antibodies acquired from an immune serum medicine.

Four Specifications of Acquired Immunity

• Specificity: Adaptive immunity can differentiate between different types of pathogens, which one is harmful or harmless. 
• Diversity: It can detect a variety of pathogens, from simple bacteria to complicated viruses. 
• Distinguish between self and non-self: It is an ability to distinguish between own body cells and foreign, harmful pathogens.  
• Memory: Adaptive immunity keeps a memory of all the pathogens it encounters throughout life. If that bacteria attack again, then the adaptive immune system has that memory to fight against them with the same antibodies generated at the first encounter. 

Cells Involved in Acquired Immunity 

On a broad basis, two types of cells are involved in acquired immunity:

S.No.	B-cells	T-cells
1.	They originate as well as develop in the bone marrow	They originate in the bone marrow and develop in the thymus
2.	They get activated after encountering a foreign pathogen	They get activated upon getting signals from B-cells and other innate immune cells.
3.	They differentiate into plasma cells (produce antibodies) and memory cells	They differentiate into T-helper cells and T-cytotoxic cells.

FAQs on Innate and Acquired Immunity:

Question 1: What are innate and Acquired Immunity?

Answers:

Innate Immunity (Non-specific Immunity) is a long-term non-specific immunity that is present in the organism by birth. Whereas Acquired immunity (adaptive immunity) is gained over the life span by getting exposed to different pathogens throughout life. 

Question 2: What are the four Types/Barriers of innate immunity?

Answer:

Following are the four barriers to innate immunity

• Physical barriers
• Physiological barriers    
• Cellular barriers
• Cellular barriers

Question 3: What are the different types of Acquired immunity?

Answer: 

Acquired immunity is of two types:

• Active Immunity: Immunity you develop after being exposed to an infection or from getting a vaccine.
• Passive Immunity: Immunity you acquire from someone or something else.