Features Of Immune Response | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

 Immune System Function

• The immune system's main role is to defend against infections.
• Lower animals rely on innate immune mechanisms like phagocytosis for protection.
• Higher animals have an adaptive immune response which is more specific and effective.

• Features of Adaptive Immune Response

  • Memory: Immune system remembers past infections for better defense.
  • Specificity: Immunity developed against one organism does not protect against others.
  • Recognition of Self and Non-Self: Immune system distinguishes between body's own cells and foreign invaders.

• Memory in Immune Response

  • First exposure to an antigen triggers memory cells for future protection.
  • Example: Vaccination introduces harmless antigens to prime the immune system for future encounters.
  • Secondary response results in rapid and abundant antibody production for quicker defense.

• Specificity in Immune Response

  • Immunity developed against one pathogen does not protect against unrelated pathogens.
  • Body can differentiate between different organisms for tailored immune responses.

• Recognition of Self and Non-Self

  • Immune system must distinguish between body's own cells and foreign invaders.
  • Failing to do so may lead to autoimmune reactions where the body attacks its own cells.
  • Mechanisms exist to recognize 'self' components to prevent attacks on the body's own tissues.

General Defence Mechanisms of the Body

• Skin

  The skin serves as a crucial barrier against pathogens. Hair, fur, and feathers protect the skin from damage. The skin's intact nature and its acidic pH (3 to 4) create a formidable barrier for pathogens. Normal flora-derived bactericidal substances also aid in skin protection. Trauma and constant wetting of the skin increase the risk of infections.

• Conjunctiva

  The conjunctiva is vulnerable to air-borne infections. The constant secretion of lachrymal fluid, containing lysozyme, helps in defending this area against pathogens.

• Respiratory Tract

  The respiratory tract encounters inhaled microorganisms. The nasal cavity's structure and mucus play a vital role in protecting against infections. Mucus contains substances that hinder bacterial growth.

• Trachea and Bronchi

  Ciliated epithelium and mucous cells line these organs, constantly washing away pathogens. Coughing helps to remove mucus and trapped microorganisms.

• Bronchioles and Lungs

  Pathogens that bypass the upper respiratory defense mechanisms are destroyed by histiocytes and lymphoid tissues in the lungs.

• Digestive Tract

  The mouth's epithelium, saliva, and stomach acidity act as defenses. Intestines rely on peristalsis and normal bacterial flora to prevent infections.

• Urino-Genital Tract

  Urine plays a cleansing role in both males and females, preventing the establishment of infections. The lympho-reticular system is a specialized defense mechanism spread throughout the body, protecting against infections.

Special Defence Mechanisms of the Body

• Lympho-Reticular System

  This system comprises specialized cells distributed throughout the body, protecting against infections. It includes phagocytic cells like neutrophils and macrophages, which can ingest foreign particles. Eosinophils play a role in allergic reactions and parasitic diseases.

Understanding Histiocytes and the Lympho-Reticular System:

• Histiocytes are fixed cells of the lympho-reticular system found in various body organs such as the omentum, alveolar walls of the lungs, Kupffer cells of the liver, and others.
• These cells play a role in removing foreign particles from the bloodstream, demonstrated by the ingestion and removal of carbon particles after injection.
• Phagocytosis, the process of destroying and removing microorganisms from the body, can occur even without specific antibodies, although the presence of antibodies enhances this process.

Development of Active Immunity:

• Active immunity is acquired by injecting killed or living microorganisms or their products to stimulate the production of specific antibodies, providing protection against natural disease for a period after immunization.
• Vaccination in domestic animals controls various infectious diseases by inducing active immunity against specific pathogens.

Passive Immunity in Newborn Animals:

• Newborn animals lack developed immunity and can acquire passive immunity from their mothers through colostrum, egg yolk, or injections of antiserum from immune individuals.
• Passive immunity transfer can also occur through antiserum injection prepared from individuals already immune to specific microorganisms.

Immune Response and Immune Reactions

• Immune responses may involve tissue cells and sometimes lead to hypersensitive reactions, autoimmune reactions against host tissues, or organ malfunctions.
• Throughout an individual's life, immune responses constantly develop in response to various stimuli, with outcomes that can be advantageous or detrimental to the host.

Antigens and Antibodies:

• Antigens are substances capable of stimulating an immune response and can be proteins, polysaccharides, or complex molecules with unique chemical groupings.
• Antibodies, produced in response to antigens, are globulin molecules that specifically bind to antigens to neutralize or eliminate them from the body.

Immunology Concepts 

• Haptens are small chemical groups of low molecular weight that do not trigger antibody production when injected alone but become antigenic when attached to a larger protein molecule (carrier molecule).
• The configuration of a hapten is crucial for recognition, more so than its chemical properties. Recognition is based on the three-dimensional shape of its outer electron cloud.
• For example, penicillin is a hapten that, when combined with a protein, forms a complex antigen capable of stimulating the production of specific antibodies for penicillin.

Bacterial Antigens

• Somatic Antigens

  • Somatic antigens in Gram-negative bacteria like Salmonella, Escherichia, Brucella, and Vibrio are made up of lipopolysaccharide-protein complexes, which are potent antigens stimulating antibody production.
  • Some purified polysaccharide fractions act as haptens, providing specificities for serological typing of bacterial groups like Salmonella and Escherichia.

• Capsular Antigens

  • Capsules found on bacterial surfaces, such as those produced by Pasteurella, Yersinia, and Klebsiella, often consist of polysaccharides or polypeptides.
  • Well-developed capsules can shield somatic antigens from their specific antibodies until the capsules are removed.

• Flagellar Antigens

  • Flagella in bacteria like Salmonella, Escherichia, and Proteus are composed of flagellin protein and serve as strong antigens.
  • Antigenic variations in flagella arise from different arrangements of amino acids in the protein molecule.

• Fimbrial or Piliate Antigens

  • Fimbriae or pili, short structures on bacterial surfaces, are antigenic and distinct from flagella.
  • Modified fimbriae like sex pili play a role in bacterial conjugation rather than disease prevention.

• Spore Antigen

  • Significant bacterial spores, such as those in Clostridium species, are relevant in animal diseases.

• Soluble Antigen

  • Bacterial species producing protein antigens called toxins, like Clostridium and Staphylococcus, induce the production of antitoxins to control infections.
  • Toxins can be converted into toxoids by mixing with formaldehyde, maintaining antigenicity while losing toxicity.

• Viral Antigens

  • Animal viruses consist of nucleic acid surrounded by a protein coat. Antibodies against viral antigens can aid in controlling infections.
  • Antibodies specific to the outer protein layer of viruses can be valuable in host defense against infections.

Immune Deficiency Disorders

• Animals with lowered resistance to infections may have hypoimmune states, showing signs like infections in the first six weeks of life.

Primary Immune Deficiency Disorders

• Combined Immuno Deficiency (CID) in Arab Horses

  Results from a genetic failure to produce and differentiate lymphoid precursor cells into B and T lymphocytes.

• Agamma globulinemia in Horses

  Caused by the inability to produce B lymphocytes due to inherited conditions.

• Selective Deficiencies of Globulins

  Examples include IgM deficiency in Arab horses, combined IgM and IgA deficiencies in horses, and transient hypogammaglobulinemia in horses.

• Lethal Trait A46

  Primary immune deficiency affecting T lymphocytes, leading to impaired cellular immunity.

• Selective IgG2 Deficiency of Cattle

  Results in increased susceptibility to infections like gangrenous mastitis and is characterized by a primary deficiency in IgG2 synthesis.

• Chediak-Higashi Syndrome

  An inherited defect affecting various animal species, including cattle, leading to weakened defense against infections due to impaired phagocytic capacity.

Secondary Immune Deficiencies

• Failure of Passive Transfer (FPT)

  Occurs when antibodies from colostrum fail to transfer to offspring, impacting their immune defense.

• Atrophy of Lymphoid Tissue

  Caused by factors like viral infections (e.g., equine herpes virus), bacterial infections (e.g., Mycoplasma spp.), and physiological stress such as birth and environmental stress.

• Toxins and Environmental Factors

  Exposure to toxins like bracken, tetrachloroethylene, and environmental pollutants can suppress immune responses and affect leucopoiesis.

Genetic engineering of bacterial antigens:

• Genetic engineering. is being applied to the preparation of protein vaccines against bacterial diseases. 
• Enterotoxigenic E.Coli, the cause of diarrhoeal diseases in young livestock contain pili on their surface which are made up of proteins.
• Distinctive immunogenic strains have been isolated for swine and calves and the genes for the proteins for the pili' have been cloned and expressed in other bacteria.

Vaccines and Hyper-Immune Serum

• Vaccines and Hyper-immune Sera:

  • The connection between surviving a microbial infection and developing immunity has been recognized since the early studies on diseases caused by microbes.
  • Jenner's 1798 work demonstrated that cowpox inoculation protected against smallpox, leading to the term "vaccination."
  • Pasteur further expanded the concept, using low-virulence strains to protect chickens from more harmful strains, coining the term "vaccination."
  • Initially related to smallpox, "vaccine" and "vaccination" now broadly refer to various immunizing agents.

• Hyper-immune Serum:

  • Serum from hyper-immunized animals, rich in antibodies, provides curative treatment or temporary protection against bacteria or toxins for 10-21 days.

• Methods for Controlling Infectious Diseases:

  • Controlling diseases through vaccination or hyper-immune serum requires tailored approaches based on the characteristics of infective agents, their life cycles, and disease pathogenesis.
  • Modifications consider factors like the nature of the infective agents, their life histories, and the age and species of affected animals.
  • Immunization methods vary in efficacy, with some diseases having satisfactory procedures, others limited in value, and a few being wholly efficient and reliable for infection control.

• Immunization and Disease Control:

  • Infections can lead to various host-parasite relationships, resulting in severe reactions, undetectable responses, or varying pathological responses.
  • Disease nature depends on factors like age, immunological response capability, affected tissues, and the pathogenic properties of the organisms.
  • Procedures for artificial immunization must be adapted to match the conditions and characteristics of different diseases.

Artificial Immunization Methods

• Artificial immunization involves two main methods to induce immunity: active and passive.

• Active Immunity:

  This method uses vaccines containing antigens from bacteria to stimulate the body to produce its own antibodies for future protection.

• Passive Immunity:

  Involves injecting hyperimmune serum with specific antibodies into an individual to provide immediate but short-lived protection.
• Active immunization through vaccines takes time for the body to produce antibodies, typically 7-10 days after vaccination.
• After receiving a vaccine, the individual remains susceptible to infection during the initial phase but becomes less susceptible as antibody levels increase.
• A booster dose of the vaccine is often required to maximize and prolong immunity.
• Passive immunity through hyperimmune serum provides immediate protection due to the direct injection of antibodies.
• However, passive immunity is short-lived, lasting only about 2-3 weeks.

Transfer of Passive Immunity

• Another way to confer passive immunity is by vaccinating the mother, who then passes on immunity to offspring through colostrum (in mammals) or egg yolk (in birds).
• For example, vaccinating ewes before lambing can protect newborn lambs against diseases like lamb dysentery through the transfer of antibodies in colostrum.

Age Consideration in Artificial Immunization

• The age of the animal is crucial in deciding the appropriate method of artificial immunization.
• Young animals rely on passive immunity since their immune systems are not fully developed to produce adequate antibodies.
• Young animals can receive passive immunity from their mothers through colostrum or via direct injection of hyperimmune serum.