Immunology Question And Answers

Immunology

• Types of Innate Immunity: Innate immunity is of three types, i.e. species, race and individual. Following are the details.
  • Species immunity: This is the immunity in the members of particular species. B. anthracis, S. typhi, etc. infect humans but not animals. These diffrences are due to physiological and biochemical differences between the tissues of various species.
  • Racial immunity: Various races within the same species can exhibit the difference in susceptibility or resistance towards the infection. This is known as racial immunity. Examples are Algerian sheep is resistant to anthrax while ordinary sheep is susceptible to it; blacks are more prone to tuberculosis as compared to whites.
  • Individual immunity: Resistance to infection varies from one individual to another of the same race and species. This is known as individual immunity. It is evident during an outbreak of infectious disease in which some individuals escape from the disease, some of them develop subclinical infection and some of them got diseased.

Types of Acquired Immunity:

Two types of Acquired Immunity

1. Active immunity
2. Passive immunity

1. Active immunity: This is induced by an infection orvaccination

• It is the resistance developed by an individual as the result of antigenic stimulus.
• When an individual is exposed to the antigen of a microbe, the individual mounts an active type of immune response to eradicate the infection and get resistant to further infection by the same microbe.
• Active immunity requires a considerable time for its development but as it develops, it lasts for years.
• Active immunity is of two types, i.e. natural and artificial:
• Natural active immunity:
  • It develops naturally due to natural contact with the microbe or its products.
  • This natural contact can lead to major invasion with clinical disease or minor invasion without clinical disease.
  • As contact with antigen occurs due to infection patient in most of cases is immune to further infection by the same pathogen for a period which is different for different diseases such as in diseases, i.e. influenza, common cold immunity last for short duration but in infections such as diphtheria, measles, etc. immunity persists for life.

• • Examples of natural active immunity are:
    1. A person who has recovered from an attack of measles develops natural active immunity.
    2. A large majority of adults in developing countries possess natural active immunity to poliomyelitis.

• Artificial active immunity: It may be acquired artificially by inoculation of bacteria, viruses or other products. Vaccines are preparations consisting of live or killed organisms.For example:

• • Live vaccines:
    1. Bacterial vaccine: Typhoral for typhoid and BCG for tuberculosis
    2. Viral vaccine: MMR for mumps, measles and rubella
  • Killed vaccines:
    1. Bacterial vaccine: Cholera vaccine for cholera
    2. Viral vaccine: Salk vaccine for polio
  • Toxoids:
    1. Various microorganism produce exotoxins such as tetanus bacilli, diphtheria bacilli, etc.
    2. The toxoids are detoxified and are used for immunization. Detoxifid toxin is a toxoid that is not toxic but antigenic.
    3. Toxoids are prepared by treating toxins with heat or formalin.
    4. As injection of toxoid is given, it produces anti-toxin which reacts with toxin and neutralizes it, for example. tetanus toxoid for tetanus.

2. Passive immunity: It is through the transfer of antibodies from an actively immunized individual.

The immunity which is acquired by transfer of readymade antibodies against microbes or their products in anotherhost is known as passive immunity. It is of two types, i.e. natural and artificial.

• Natural passive immunity:
  • In newborn babies, acquired active immunity is absent due to the growing immune system but they are resistant to many infections.
  • This resistance occurs due to the transfer of readymade antibodies from mother to fetus which lasts for 3 to 4 months.
  • Transfer of antibody from mother to fetus occur in two ways, i.e. during intrauterine life, the transmission of antibodies from mother to fetus occurs through the placenta to fetal circulation.
  • Here IgG type of antibody neutralizes toxins and viruses.
  • After the birth, milk or colostrum of the mother is absorbed through the intestinal mucosa.
  • Here IgA type of antibody provides local intestinal immunity.

• Artificial passive immunity
  • Immunity is produced artificially by injecting antibodies produced in some other human or animal.
  • Antibodies remain in effective quantity for 10 days only.
  • For example, half-life of diphtheria antitoxin is a week.
  • For artificial passive immunity, the hyperimmune serum is prepared in horses, sheep, goats, rabbits, guinea pigs, or human beings.
  • Serum prepared is antitoxic, antibacterial, or antiviral in nature and is known as antiserum or antitoxin.

• Innate immunity
  • Species
  • Racial
  • Individual
• Acquired immunity
  • Active immunity
    1. Natural
    2. Artificial
  • Passive immunity
    1. Natural
    2. Artificial
• Miscellaneous
  • Combined immunization
  • Adoptive immunity
  • Local immunity
  • Herd immunity

• Live attenuated vaccines: Attenuation is achieved by the aging of culture, culture at high temperature, and selection of mutant. For example:
  • Vaccines against bacteria: Mycobacterium tuberculosis, E. coli, Vibrio cholerae.
  • Vaccines against viruses: Polio, yellow fever, rabies, and mumps.
• Killed vaccines: For this the organisms are killed by heat, formalin, phenol, and UV light, for example, .whooping cough, cholera, polio and measles.
• Toxoid vaccines: They are exotoxins which are treated with formalin to destroy their toxicity and provide immunity, example formal toxoids of diphtheria and tetanus.
• Subunit vaccine: They consist of only relevant immunogenic material, for example, Capsid proteins of non-enveloped icosahedral viruses.

• It may be acquired artificially by inoculation of bacteria, viruses, or other products.
• Vaccines consist of live or killed organisms.
• Live vaccines consist of live microorganisms with decreased virulence. These are prepared by attenuated strains of microorganisms. Immunity by these lasts for several years. In live vaccines, booster doses are not needed.
• These can be administered by route of natural infection or parenteral.
• For example:
  • Bacterial vaccine: Typhoral for typhoid and BCG for tuberculosis
  • Viral vaccine: MMR for mumps, measles and rubella
• Killed vaccines consist of killed and inactivated organisms. Preparation is done by inactivating of microorganisms by heat, phenol, formalin, etc. These vaccines do not initiate infection and there is no multiplication of microorganisms. Its level of immunity is less as compared to live vaccine. It remains for short duration so booster doses are necessary. These vaccines are given by parenteral route.
  • Bacterial vaccine: Cholera vaccine for cholera
  • Viral vaccine: Salk vaccine for polio
• Toxoids: Various microorganism produce exotoxins such as tetanus bacilli, diphtheria bacilli, etc. The toxoids are detoxified and are used for immunization. Detoxifid toxin is a toxoid which is not toxic but antigenic. Toxoids are prepared by treating toxin with heat or formalin. As  injection of toxoid is given, it produces antitoxin which reacts with toxin and neutralizes it, for example, Tetanus toxoid for tetanus.

• Immunity is produced artificially by injecting antibodies produced in some other human or animal.
• Antibodies remain in effective quantity for 10 days only.
• For example, half-life of diphtheria anti-toxin is a week.
• For artificial passive immunity, the hyperimmune serum is prepared in horses, sheep, goats, rabbits, guinea pigs, or human beings. Serum prepared is antitoxic, antibacterial or antiviral in nature and is known as antiserum or antitoxin.
• Preparation of antiserum is done by injecting specific antigen which forms specific antibody, for example, Rabies antiserum
• Preparation of antitoxin is done by injecting toxin or toxoid, for example, antitetanus serum, antisnake venom, etc.
• Antisera and antitoxins are applicable in clinical situations, i.e. anaphylactic reactions where there is no other option.

• For prophylaxis and in clinical emergencies where immediate and temporary protection is required such as tetanus, snake bite, etc.
• For suppressing active immunity, i.e. in Rh-negative women with Rh-positive babies.

• Species immunity: It is the resistance to a pathogen which is shown by all members of particular species, for example Bacillus anthracis infect human being but not chickens.
• Racial immunity: In single species diffrent races may ex-hibit diffrences in resistance to infection. It is known as racial immunity, for example , American negroes are more susceptible to tuberculosis as compared to whites.
• Individual immunity: Resistance to infection varies with different individuals of same race and species. It is known as individual immunity, for example, Homozygous twins exhibit similar degrees of susceptibility or resistance to tuberculosis. In contrast, it is not seen in heterozygous twins.

• Age: Fetus and old age carries high susceptibility to infections. In fetus immune system is immature while in old age waning of immune response is present.
•  Hormones: Various hormonal disturbances such as diabetes mellitus, adrenal infection, and hypothyroidism enhance susceptibility of infections. Corticosteroids depress immune system.
•  Nutrition: Malnutrition leads to reduction of humoral and cell mediated immune systems.

• Skin: It provides bactericidal secretion and leads to diminishing of bacterias. High concentration of salt, sebaceous secretions and long chain fatt acids contribute to bactericidal activity.
• Respiratory tract: Inhaled particles get arrested in nasal passages on moist mucous membrane surfaces. Mucous secretions of respiratory tract have hair like cilia which propels particles towards pharynx which
• are swallowed or coughed out.
  Intestinal tract: Normal bacterial flra of intestine provides protective effct by preventing colonization of pathogenic bacteria.
• Conjunctiva: Tears flsh away bacteria and foreign particles.

Active immunity

• Active immunity is the resistance that is developed by an individual in relation to contact with an antigen.
• The contact with antigen may be in the form of natural infection or via vaccination.
• As antigen enters it stimulates the immune system to form antibodies and there is production of immunologically active cells.
• Active immunity develops after a latent period which is required for immune system to act but once developed, the active immunity is long lasting.
• Active immunity is subdivided into two types, i.e. natural and artificial.
• Natural active immunity is gained through clinical or subclinical infection while artificial immunity is induced through vaccination.
• Active immunity leads to stimulation of both humoral and cell-mediated immunity which works parallel.

• Humoral immunity is antibody mediated.
• It depends on synthesis of antibodies by plasma cells.
• Plasma cells produce specific antibody which
• circulates and combines specifically with the antigens and modifies their activity.

• Cell-mediated immunity depends on lymphocytes which are developed against various antigens.
• Antibody synthesis occurs in response to the secreted antigens, but their role is limited.
• Cell-mediated immunity produced by sensitized T lymphocytes provides resistance in chronic bacterial infections.

• Natural Active Immunity
  • It develops naturally due to natural contact with the microbe or its products.
  • This natural contact can lead to major invasion with clinical disease or minor invasion without clinical disease.
  • As contact with antigen occurs due to infection patient in most of the cases is immune to further infection by same pathogen for a period which is different for different diseases such as in diseases, i.e. influenza, common cold immunity last for a short duration but in infections such as diphtheria, measles, etc. immunity persists for life.
  • Examples of natural active immunity:
  • A person who has recovered from an attck of measles develops natural active immunity.
  • A large majority of adults in developing countries posses natural active immunity to poliomyelitis.

• Artificial Passive Immunity: