Types of immunity

Types of Immunity: Innate, Acquired and Herd

1. Types OF immunity Nidhi Saxena Department of Microbiology

2. Immunity Immunity  is derived from Latin word  “ immunis ”  which means free from burden. In this case burden refers to disease caused by microorganisms or their toxic products. Immunity  is defined as the state of resistance or in susceptibility to disease caused by particular microorganisms or their toxic products. In biology,  immunity  is the balanced state of multicellular organisms having adequate biological defenses to fight infection, disease, or other unwanted biological invasion, while having adequate tolerance to avoid allergy, and autoimmune diseases.

3. Factors affects Immunity Host resistance Dosage of organisms Virulence of organisms

4. Types of immunity Natural or Innate Immunity Acquired or Adaptive or Specific Immunity Species immunity Racial immunity Individual immunity Active Acquired immunity Passive Acquired immunity Natural Artificial Natural Artificial

5. Natural or innate immunity Immunity with which an individual is born is called innate or natural immunity. Innate immunity is inherited by the organism from the parents and protects it from birth throughout life. Innate immunity is provided by various components such as Skin, mucus membrane, Phagocytic cells etc. Innate immunity acts as first line of defense to particular microorganisms.

6. Types of innate immunity 1. Species immunity: If one species is resistant to certain infection and the other species is susceptible to the same infection then it is called as species immunity. Anatomic, physiological and metabolic differences between species determine species immunity. For example, Birds are resistant to anthrax but Human are susceptible. It is simply because higher body temperature of birds kills  Bacillus   anthracis . Anatomic differences between species also determine species immunity. For example, Human are more susceptible to skin infection whereas Cattles are more resistant to the same skin infection. It is because of tough and hairy skin (hides) of Cattles.

7. 2. Racial immunity: If one race is susceptible while other race is resistant to same infection, then it is called Racial immunity. For examples; certain African race are more resistant to malaria and yellow fever but Asian or Americans are susceptible to same infection. Racial immunity is determined by difference in Socio-economic status, habitat, culture feeding habits, environments, genetic, etc.

8. 3. Individual immunity: If one individual of certain race or cast is resistant while other individuals of same race or cast are susceptible to certain infection, then it is called as individual immunity. Individual immunity is determined by various factors such as health status, nutritional status, previous illness, personal hygiene, genetic differences etc. For examples; Individual with genetic deficiency of glucose-6 phosphate dehydrogenase are resistant to Malaria.

9. Mechanism of innate immunity Anatomical barrier Physicochemical barrier Phagocytic barrier or Phagocytosis Inflammatory barrier or Inflammation

10. Anatomical barrier 1. Skin: Skin consists of two distinct layer; a thin outer layer called epidermis and thick inner layer called dermis. Epidermis consists of mostly dead cell filled with keratin. Dermis is composed of connective tissue, hair follicle, sebaceous gland and sweat gland. Skin provides first line of defense by preventing entry of microorganisms. However skin may be penetrated by injury or insects.

11. 2. Mucous membrane: Mucus secreted by mucous membrane traps the microor­ganisms and immobilises them. Microorganisms and dust particles can enter the respiratory tract with air during breathing which are trapped in the mucus. The cilia sweep the mucus loaded with microorganisms and dust particles into the pharynx (throat). From the pharynx it is thrown out or swallowed for elimination with the faeces .

12. Physiochemical barrier Acid of the stomach kills most ingested microorganisms Bile does not allow growth of microorganisms Cerumen (ear wax) traps dust particles, kills bacteria and repels insects Lysozyme is present in tissue fluids and in almost all secretions e.g. sweat, urine, tears, saliva etc. Nasal Hair. They filter out microbes and dust in nose Urine. It washes microbes from urethra Sebum (sweat). It forms a protective acid film over the skin surface that inhibits growth of many microbes.

13. phagocytosis Phagocytosis is an important defense mechanism of host to provide immunity. Most of the bacteria that enter into host are killed by phagocytic cells such as Neutrophils, monocytes and macrophages. Phagocytosis is an example of endocytosis. There are two types of endocytosis; phagocytosis and pinocytosis.

14. inflammation Inflammation  is an important defense mechanism of host to prevent infection. It is induced in response to tissue damage caused by microorganism, toxins or by mechanical means. The inflammation may be acute; for eg . in response to tissue damage or chronic ; for eg. Arthritis, cancer etc. Main aim of inflammation is to prevent spread of injected microorganism or toxin from site of injection and kill them on spot by phagocytosis.

15. Characteristics of Inflammation Rubor : Redness Tumor: Swelling Calor : Heat Dolor: Pain Functio laesa : Loss of function

16. Steps of inflammatory response Tissue damage caused by toxin, microorganism or mechanical injury release histamine Vasodilation : Histamine causes blood vessels vasodilation. Increased permeability : Histamine increases the permeability of blood capillaries so that fluid accumulates & causes edema. Extravasation : Neutrophil migrates to the site of tissue damage by the process of chemotaxis and passes through capillaries wall and enter into tissue space by the process called extravasation.

17. 5. Phagocytosis : Neutrophil kills the microorganism or toxins by phagocytosis and release molecular mediators that contributes to inflammatory response. At the same time activates effectors cells. 6. Inflammatory response : As inflammatory response develops, various cytokines and other inflammatory mediators act on endothelium of local blood vessels, including increased expression of cell adhesion molecules (CAMs). The epithelium is then said to be inflamed. Neutrophils are the first cell types to bind to inflamed endothelium and extravasate into tissue.

18. Acquired immunity Immunity which is developed later in life after microbial infection in host is called as Acquired or developed immunity. For example, If an individual is infected with chicken pox virus, he/she become resistant to same virus in later life. Acquired immunity is provided by Antibodies and certain T-lymphocytes. Components of acquired immunity such as Antibodies and T- cells are specific to particular microorganism. Therefore acquired immunity is also known as Specific immunity.

19. Types of acquired immunity 1. Active immunity: If host itself produces antibodies, it is called active immunity. Artificial active immunity: Immunity provided by vaccination. Natural active immunity: Immunity provided by natural infection. 2. Passive immunity: If host does not produce antibodies itself but antibodies produced in other host provides immunity, than it is known as Passive immunity. Natural passive immunity: IgG antibody produced in mother cross placenta and protects fetus up to 6 months. Artificial passive immunity: If preformed antibody are injected into host for immunity. Eg . Anti-venom, Rabies vaccine

20. Characteristics of Acquired Immunity Specificity : It is the ability to differentiate between antigens. Diversity : It can recognise a vast variety of antigens. Discrimination between Self and Non-self : It can recognise and respond to foreign molecules (non-self) and can avoid response to those molecules that are present within the body (self) of the animal. Memory : When the immune system encounters a specific foreign agent, (e.g., a microbe) for the first time, it generates immune response, eliminates the invader and retains the memory for second encounter.

21. Components of acquired immunity Acquired immunity has two components: Humeral immunity or Antibody mediated immune system (AMIS) Cellular immunity or cell mediated immune system (CMIS)

22. Humeral immunity or Antibody mediated immune system (AMIS) The word ‘humor’ mean fluid. It consists of antibodies that circulate in the body fluids like blood plasma and lymph. В lymphocytes (B cells) produce antibodies that regulate humoral immunity. Humoral immunity or antibody-mediated immune system (AMIS) provides defence against most extracellular bacterial pathogens and viruses that infect through the respiratory and intestinal tract. Role of AMIS: The AMIS protects the body from viruses, some bacteria and toxins that enter the body fluids like blood and lymph.

23. Cellular immunity or cell mediated immune system (CMIS) Lymphocytes are of two types: T lymphocytes and В lymphocytes. Because T lymphocytes (T cells) mature in the thymus, this immunity is also called T- cell immunity. The T-cells play two important functions—effector and regulatory. The effector function includes cytolysis (destruction of cells by immune processes) of cells infected with microbes and tumour cells and lymphokine production. The regulatory functions are either to increase or to suppress other lymphocytes and accessory cells.

24. Herd immunity also known as community immunity. Herd immunity occurs when a high percentage of the community is immune to a disease (through vaccination or other methods), making the spread of this disease from person to person unlikely. Even individuals not vaccinated are offered some protection because the disease has little opportunity to spread within the community. Vaccines prevent many dangerous and deadly diseases. In India polio have been stamped out because of vaccination. Herd immunity

25. Protection of those without immunity. Evolutionary pressure. Serotype replacement. Eradication of diseases. Effects of Herd immunity

26. Individuals who are immune to a disease act as a barrier in the spread of disease. There are certain groups of people who cannot get vaccinated and are vulnerable to disease:- babies, pregnant women and immunocompromised people, such as those receiving chemotherapy or organ transplants. If enough people are vaccinated against dangerous diseases, those who are susceptible and cannot get vaccinated are protected because the germ will not be able to “find” those susceptible individuals. Mechanism of Herd immunity

27. 1) Innate herd immunity: It is genetically determined physiological changes with respect to antibody production or other defence mechanism in a herd. It does not depend on the previous exposure of herd with infection or it may arise in a herd through prolonged exposure to an infection or natural selection. 2) Acquired herd immunity: It is a type of herd immunity where a sufficient number of its members have actually been exposed naturally or artificially to infectious agents during their lifespan. This kind of exposure may be made very early in life. Types of herd immunity

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