Immunity And Immune System: Definition, Difference, Examples

Immunity is the body's natural defence system that protects against infection and diseases. This is defined as the body's ability to recognise and fight harmful pathogens through different complex mechanisms. There are two main types of immunity. Two main types of immunity are innate immunity which is the body’s initial, non-specific response and acquired immunity, which develops specific responses over time through exposure to antigens. Being part of the human health disease chapter class 12th Biology it becomes important from an exam point of view.

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This Story also Contains

1. What is Immunity?
2. Types of Immunity: Innate and Adaptive
3. Cells Involved in Innate Immunity
4. Acquired Immunity
5. Characteristics of Adaptive Immunity
6. Different Immune Response Mechanisms
7. Types of Acquired Immunity
8. Diagram Representing Lymphoid Organs
9. Lymphoid Organs
10. Disorders of the Immune System
11. Boosting the Immune System

What is Immunity?

The immune system is the body’s defence, especially against pathogenic agents, which include bacteria, viruses, and other invaders. The immune system is a sophisticated process that embraces cells, tissues, and vital organs that protect the body. Immunity, meaning in a biological view, consists of both the natural immunity and the immunity one gains from a vaccine. Some of the major points about immunity are discussed below:

• The immune system includes various cells (like white blood cells) and organs (such as lymph nodes, spleen, and thymus) that work together to detect and destroy pathogens.

• Immune cells are produced by B-cells, antibodies are proteins that specifically target and neutralize foreign agents like bacteria and viruses, marking them for destruction.

• Vaccines help the immune system to develop adaptive immunity by introducing harmless antigens.

• This allows the body to recognize and respond to future infections more effectively based on the immune system's memory cells.

Immune System

The immune system is a protection system in the body that prevents pathogen invasion by bacteria, viruses, and fungi, among others. It includes two main components: innate immunity, which gives a quick and generalised reaction, and adaptive immunity, which offers a precise response to the invaders through a specific reaction.

Immunology, as defined by the above meanings, is the branch of medicine that is concerned with the identification of the body and the immune system's response to foreign particles.

It focuses on the aspects of the immunological structure that are inherent and acquired and the conventional and abnormal roles they play when they are not well. Immunologists also strive to establish effective vaccines and immunotherapies for strengthening or modulating immune responses.

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Types of Immunity: Innate and Adaptive

Immunity is classified into two main types: innate immunity and acquired immunity. Innate immunity is immediately available at birth and provides primary protection, while acquired immunity is developed as the organism responds to various pathogens as it grows.

Types of Barriers

There are primarily 5 types of barriers and the basic facts about them are discussed below in the table:

Cells Involved in Innate Immunity

Various cells are involved in innate immunity:-

• Phagocytes: Engulf and digest pathogens.

• Macrophages: Destroy pathogens, present antigens, and initiate adaptive immunity.

• Neutrophils: First responders that immediately eliminate pathogens.

• Natural Killer (NK) Cells: Targets and destroys infected or malignant cells.

• Mast Cells: Release histamine and are involved in allergies and defence against parasites.

• Eosinophils: Defend against parasites which participate in allergic responses.

• Basophils: Contribute to inflammation and allergic reactions.

• Dendritic Cells: Present antigens that help connect innate and adaptive immunity.

Acquired Immunity

Acquired immunity, also known as adaptive immunity, is the second level of protection the body puts up against pathogens. It is defined as the enhanced ability of the immune system to recognise specific pathogens and respond to them faster at the second time of meeting the same pathogens. This form of immunity is attained progressively and functions with the help of certain specialised cells and processes.

Cells involved in acquired immunity

Primarily, 2 kinds of cells are involved in acquired immunity:

B Cells

B cells are other large mononuclear leukocytes that are involved in the acquired immunity besides actively participating in the humoral immunity. They produce substances that form a lock-key system with particular antigens that are present on the pathogen.

On stimulation, the B cells differentiate through proliferation to plasma cells or memory B cells and start producing antibodies. B cells also differentiate into memory B cells to give the organism long-term immunity.

T Cells

T lymphocytes are significant leukocytes that are involved in acquired immunity, especially in cell-mediated immunity. Effector T cells, also known as cytotoxic T cells, CD8 T cells are involved in killing infected or cancerous cells by apoptosis.

CD4+ T cells or helper T cells mobilize immune responses through the active identification of antigens and releasing substances known as cytokines which stimulate other immune cells. Memory T cells are alive after the first immune response and can give quick and stronger responses when encountering similar antigens again.

Characteristics of Adaptive Immunity

There are various characteristics of acquired immunity:

• Specificity: Specific immunity targets specific antigens that are involved in the pathogens, and this makes the immune response very fit.

• Memory: The ability of the immune system to mobilise enhanced quick and aggressive response to the pathogen previously encountered is called immunological memory.

• Diversity: Specific immunity can find several pathogens because of the many types of antibodies and T-cell receptors present in the immune system.

• Distinction between the self and non-self: One more capability of the immune system is the ability to tell the difference between the organism’s cells and cells that belong to pathogens, and thus refrain from attacking the organism’s tissues.

Different Immune Response Mechanisms

There are 2 kinds of immune response mechanisms:

Humoral Immune Response

The two main components of the circulating arm of the immune response include B cells, which are types of lymphocytes that target toxins and other pathogens or foreign molecules based on their antigens. After binding with antigen, B cells become sensitised and differentiate into plasma cells that release large amounts of antibodies.

They are protein substances that move in the bloodstream and through the lymphatic system, where they adhere to antigens in the pathogen’s body. This binding can either kill the pathogen, tag the pathogen for destruction by phagocytes, or activate the complement system to improve the killing of the pathogen.

Cell-Mediated Immune Response

Cell-mediated immunity entails the participation of T cells, another type of lymphocyte, in the body tissues. It is required for killing intracellular parasites like viruses and specific bacteria as well as for the identification of the transformed cell. Cytotoxic T cells, or CD8-positive cells, recognise and destroy infected or malignant cells through apoptosis.

The helper T cells are important in controlling the immune response as they secrete cytokines which stimulate other immune cells, such as macrophages and cytotoxic T cells.

Types of Acquired Immunity

Two types of acquired immunity exist:

Active Immunity

Active immunity occurs when the immune system of the body produces antibodies that are specific to the antigen or activate the T cells. However, it can be initiated naturally due to an infection or artificially through the administration of vaccines. The common memory cells that are developed during active immunity include memory B cells and memory T cells that provide longer protection on subsequent exposures to the same antigen. Active immunity is pathogen-specific and offers highly effective, long-lasting protection.

Passive Immunity

All forms of passive immunity are obtained when antibodies that have been directly provided and already exist in the body are administered to another body. This transfer can happen transplacentally, for example, through the passing of maternal antibodies to the foetus or taro milk.

In the case of passive immunity, the antibodies transferred to the recipient’s body offer immediate protection, with this protection being temporary since the antibodies will be metabolised and expelled for elimination in the body. It is highly valuable in cases where prompt coverage is required or where an organism is incapable of producing an adequate immune response, for example, in newborns and HIV-positive clients.

Autoimmunity

Autoimmunity is characterised by the immune system attacking body tissues, and this conditions the individual for rheumatoid arthritis, and type 1 diabetes, among others.

Vaccines

Vaccines can be described as processed substances that are used to enhance the body’s immunity to particular diseases. They rely on copying symptoms of diseases and causing the body’s defence mechanisms to be activated without the development of conditions.

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Diagram Representing Lymphoid Organs

Lymphoid Organs

Lymphoid tissues are those tissues that contribute to the formation, differentiation, and activation of immune cells.

Primary Lymphoid Organs

• Bone Marrow: More specifically, bone marrow is the part of the human body that is responsible for producing all types of blood cells, the red blood cells and the white ones included.

• Thymus: It is in the thymus that T cells develop to be able to respond to a given antigen.

Secondary Lymphoid Organs

• Spleen: The spleen is involved with blood filtering as well as leading the immune response by presenting the antigens to the cells involved in the immune response.

• Lymph Nodes: Lymph nodes act as a filter for the lymph as well as a place where containing immune cells harmonise as well as plan on how best to deal with the pathogen.

Tertiary lymphoid organs

Tertiary lymphoid organs are observed in the zones of chronic inflammation and are involved in local immune processes.

How the Immune System Works

The working mechanism of the immune system is explained below:

• Recognition of Pathogens: Organisms of disease-causing agents are identified by the immune cells through specific antigens, which are located on the outer membrane of the pathogens.

• Response to Pathogens: When it senses a pathogen, the immune system initiates an attack to get rid of it. This also involves stimulation of the immune cells and resources, the release of antibodies, as well as inflammation.

• Primary Immune response: This is the first time the immune system comes across the pathogen, causing activation and multiplication of immune cells.

• Secondary Immune response: The secondary immune response is usually faster and more efficient due to the point that it contains memory cells that are acquainted with the pathogen.

• Role of Memory Cells in Acquired Immunity: Some cells in the body keep information about the pathogens that have been encountered before to ensure a quick and efficient response.

Disorders of the Immune System

Major disorders of the Immune system are discussed below:

• Autoimmune diseases: Autoimmune diseases are conditions where the immune system turns against the body and starts attacking the body’s tissues. Some basic examples are:

• Rheumatoid Arthritis: The immune system targets the joints of the body causing inflammation.

• Type 1 Diabetes: The immune system of the body malfunctions and goes after the insulin-producing cells in the pancreas.

• Immunodeficiency disorders: Immunodeficiency disorders are those in which the body’s immune system is compromised in some manner.

• HIV/AIDS: HIV infects those cells and destroys the body’s defence system, which is the immune system, resulting in AIDS.

• SCID (Severe Combined Immunodeficiency): An inherited disease in which the body’s ability to fight infections is significantly impaired.

• Allergies and Hypersensitivities: Allergy is a condition where the immune system of the body behaves abnormally, resulting in response to substances that do not pose any threat to the body, including pollen and certain foods, and this results in some symptoms such as sneezing, itching and swelling of certain parts of the body.

Boosting the Immune System

• Importance of a Healthy Diet: Vitamin intake, Minerals, and antioxidants; The overall functioning and strength of the immune system can be attributed to a vitamins, minerals, and antioxidant-rich diet. It is estimated that the foods that must be taken include fruits, vegetables, nuts, lean meats, beans, and dairy products.

• Role of exercise: Physical activity increases circulation, meaning immune cells are transported throughout the body more effectively, and immune capabilities increase.

• Vaccination: Vaccines are substances that help the body organise the production of antibodies without causing sickness, thus offering the body defence against diseases.

• Adequate sleep and stress management: Stress and sleep management form critical components of the immune system since the body cannot fight diseases when it is stressed or has had inadequate rest. Both of them have a deep influence on the immune system and health status of the individual.

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