Difference Between Innate and Adaptive Immunity

Main Difference – Innate vs Adaptive Immunity

Innate immunity and adaptive immunity are the two categories of the immune system of animals. The immune system consists of a collection of molecules, cells, and tissues, which protect the body from various pathogens and toxins. Innate immunity is always present in the body while adaptive immunity only occurs in response to exposure to an external factor. The main difference between innate immunity and adaptive immunity is that innate immunity generates a non-specific immune response against the pathogen whereas adaptive immunity generates a specific immune response against a particular pathogen.

Key Areas Covered

1. What is Innate Immunity
      – Definition, Components, Role
2. What is Adaptive Immunity
      – Definition, Components, Role
3. What are the Similarities Between Innate and Adaptive Immunity
      – Outline of Common Features
4. What is the Difference Between Innate and Adaptive Immunity
      – Comparison of Key Differences

Key Terms:  Adaptive Immunity, Antibody, Antigen, Cell-Mediated Immunity, Humoral Immunity, Innate Immunity, Phagocytes, Physical and Chemical Barriers

What is Innate Immunity

Innate immunity refers to a naturally occurring immunity by the genetic constituents and the physiology of a person. Innate immunity is present at birth, and it lasts throughout the lifetime. Prior exposure to pathogens is not required by innate immunity. The removal of pathogens by the innate immunity occurs either internally or externally. The external defense serves as the first line defense against pathogens, and it is achieved by the physical and chemical barriers. Saliva, tears, skin, mucus linings, stomach acid, and some of the bacteria in the gut serve as barriers, preventing the entering of pathogens to the tissues of the body. The second line defense is the internal defense mechanisms of the innate immunity. Various types of phagocytes serve as internal barriers, preventing the growth and reproduction of pathogens inside the tissues. Natural killer cells, macrophages, monocytes, neutrophils, mast cells, and dendritic cells are examples of cells involved in the innate immunity. These cells destroy pathogens by phagocytosis. They also activate the complement system of the body as well as adaptive immunity. The cells involved in innate immunity are shown in figure 1.

Figure 1: Cells of Innate Immunity

Both external and internal mechanisms of the innate immunity generate non-specific immune responses against the pathogens.

What is Adaptive Immunity

Adaptive immunity refers to an acquired immunity which is mediated by T cells and B cells and is characterized by an immunological memory. It serves as the third line defense of the body. The activation of the adaptive immunity occurs in response to an overcoming of the second line barriers by a particular pathogen. Cell-mediated immunity and humoral immunity are the two types of adaptive immunity. Cell-mediated immunity is mediated by cytotoxic T cells, which induce the cell death of infected cells. The helper T cells are the other type of T cells that activate B cells to produce antibodies. The production of specific antibodies against a particular pathogen occurs in humoral immunity. The corporation between first line, second line, and third line defenses are shown in figure 2.

Figure 2: First Line, Second Line, and Third Line Defenses

Due to its ability to respond to a large number of pathogens, adaptive immunity is considered as possessing a higher diversity. Once it responds to a particular pathogen, the adaptive immune system keeps the memory of the pathogen, developing a strong immune response in the second time exposure.

Similarities Between Innate and Adaptive Immunity

• Both innate and adaptive immunity are two types of immunities that protect the body from harmful pathogens and toxins.
• Both innate and adaptive immunity consists of molecules, cells, and tissues, which fight against the pathogens.

Difference Between Innate and Adaptive Immunity

Definition

Innate Immunity: Innate immunity refers to a naturally occurring immunity by the genetic constituents and the physiology of a person.

Adaptive Immunity: Adaptive immunity refers to an acquired immunity, which is mediated by T cells and B cells and is characterized by an immunological memory.

Alternative Names

Innate Immunity: Innate immunity is known as natural immunity.

Adaptive Immunity: Adaptive immunity is known as acquired immunity.

Specificity

Innate Immunity: Innate immunity generates a non-specific immune response.

Adaptive Immunity: Adaptive immunity generates a specific immune response.

Presence

Innate Immunity: Innate immunity is always present in the body.

Adaptive Immunity: Adaptive immunity only occurs in response to exposure to an external factor.

Response

Innate Immunity: Since innate immunity provides the first line defense against the pathogens, it generates a rapid response.

Adaptive Immunity: Adaptive immunity is delayed 5-6 days.

Components

Innate Immunity: Plasma proteins, phagocytes, physical and chemical barriers are the components of the innate immunity.

Adaptive Immunity: Humoral and cell-mediated immunity are the components of the adaptive immunity.

Physical and Chemical Barriers

Innate Immunity: Temperature, pH, skin, and mucous membranes are the barriers of the innate immunity.

Adaptive Immunity: Lymph nodes, spleen, and lymphoid tissues are the barriers of the adaptive immunity.

Memory Cells

Innate Immunity: Innate immunity does not develop memory cells.

Adaptive Immunity: Adaptive immunity develops memory cells.

Diversity

Innate Immunity: Innate immunity possesses a less diversity.

Adaptive Immunity: Adaptive immunity possesses a higher diversity.

Potency

Innate Immunity: Innate immunity is less potent.

Adaptive Immunity: Adaptive immunity exhibits a higher potency.

Allergic Reactions

Innate Immunity: Innate immunity does not produce allergic reactions.

Adaptive Immunity: Adaptive immunity develops allergic reactions; immediate and delayed hypersensitivity.

Activation of the Complement System

Innate Immunity: Innate immunity activates the complement system through the alternative and lectin pathway.

Adaptive Immunity: Adaptive immunity activates the complement system through the classical pathway.

Time Span

Innate Immunity: Once developed for a particular pathogen, the innate immunity remains throughout the lifetime.

Adaptive Immunity: Adaptive immunity can last for the lifetime or for a short period of time.

Inheritance

Innate Immunity: Innate immunity is inheritable.

Adaptive Immunity: Adaptive immunity is not inheritable.

Examples

Innate Immunity: The redness and swelling caused by white blood cells around a wound is an example of an innate immune response.

Adaptive Immunity: Vaccination against a virus is an example of adaptive immunity.

Conclusion

Innate and adaptive immunity are the two types of mechanisms of the immune system of animals. They protect the body against pathogens. Innate immunity generates first line and second line immune responses. Adaptive immunity generates third line immune responses. The immune response is non-specific in innate immunity, and it is specific in adaptive immunity. The main difference between innate and adaptive immunity is the type of mechanisms and the specificity of the immune responses generated by them.

Image Courtesy:

1. “Innate Immune cells” By Template drawing and caption text from “The Immune System” (pdf) (Public Domain) via Commons Wikimedia
2. “2211 Cooperation Between Innate and Immune Responses” By OpenStax College – Anatomy & Physiology, Connexions Web site., Jun 19, 2013. (CC BY 3.0) via Commons Wikimedia