Immunity and Immunizing Agents


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Immunity and Immunizing Agents : 

Immunity and Immunizing Agents Dr. Muhammedirfan H. Momin Assistant Professor Community Medicine Department Government Medical College Surat.


THE IMMUNE SYSTEM We all get sick sometimes...but then we get better. What happens when we get sick? Why do we get better?

What is immunity? : 

What is immunity? Immunity is the body's ability to fight off harmful micro-organisms –PATHOGENS- that invade it. From the Latin word “immunis”—exempt Immunity involves the antigen-antibody response The immune system produces antibodies or cells that can deactivate pathogens.

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The immune system recognizes, attacks, destroys, and remembers each pathogen that enters the body.  It does this by making specialized cells and antibodies that render the pathogens harmless. For each type of pathogen, the immune system produces cells that are specific for that particular pathogen.

Functions of the Immune System : 

Functions of the Immune System Immune System has 3 main functions: Protect the body from pathogens Remove dead or damaged tissue and cells Recognize and remove abnormal cells that have abnormal cell growth and development (i.e. cancer cells)

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The Immune System - includes all parts of the body that help in the recognition and destruction of foreign materials.  White blood cells, phagocytes and lymphocytes, bone marrow, lymph nodes, tonsils, thymus, and your spleen are all part of the immune system.


ANATOMY OF THE IMMUNE SYSTEM The immune system is localized in several parts of the body immune cells develop in the primary organs - bone marrow and thymus (yellow) immune responses occur in the secondary organs (blue)


ANATOMY OF THE IMMUNE SYSTEM Thymus – glandular organ near the heart – where T cells learn their jobs Bone marrow – blood-producing tissue located inside certain bones blood stem cells give rise to all of the different types of blood cells Spleen – serves as a filter for the blood removes old and damaged red blood cells removes infectious agents and uses them to activate cells called lymphocytes Lymph nodes – small organs that filter out dead cells, antigens, and other “stuff” to present to lymphocytes Lymphatic vessels – collect fluid (lymph) that has “leaked” out from the blood into the tissues and returns it to circulation

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White blood cells called macrophages trap and engulf cell debris and pathogens. Other white blood cells, called Lymphocytes - are a type of white blood cell capable of producing a specific immune response to unique antigens. They produce antibodies which are chemicals that mark pathogens for destruction.

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Once a white cell has left the blood vessel and migrated to the enemy, the next job is to EAT the microbe. Macrophages--engulf and destroy foreign substances, damaged cells, and cellular debris The macrophage is a large phagocyte. A phagocyte is an eating cell (phago = "eating", cyte = "cell") which engulfs invaders.

Macrophage and E. coli : 

Macrophage and E. coli ©Dennis Kunkel Microscopy, Inc.,

Lymphocytes : 

Lymphocytes Are the cells primarily responsible for the immune response Two types: T-lymphocytes—T-cells B-lymphocytes—B-cells

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Helper T cells: identifies the enemy and sends out the troops Killer T cells: kills cells of the body that have been invaded by antigens B cells: produces antibodies

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It has been estimated that during our lifetime, we will encounter a million foreign antigens capable of causing disease, and our bodies need the same amount of lymphocytes to defend against them.   There will always be a different type of lymphocyte for each possible antigen.

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When an antigen (Ag) is introduced into the human body, it stimulates the production of antibodies (Ab). Micro-organisms (and their toxins) and vaccines are antigens which evoke an immune response. The immune response is two types:- 1) The primary response: when an Ag is introduced into the body for the first time, there is a latent period of 3-10 days before Abs appear in the blood. A peak is quickly reached and the level of Abs gradually falls over a period of weeks or months.

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2) The secondary (booster) response: the response to a booster dose of the same Ag differs in a number of ways from the primary response: - has a shorter latent period and more rapid production of Abs. - Abs are produced in abundance and a high level is maintained for a longer period. - the Abs produced tend to have a greater capacity to bind to the Ags. The accelerated response is attributed to the immunological memory.

Active immunity : 

Active immunity Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and is characterized by the production of antibodies by the host.

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Active Immunity occurs when one makes his/her own antibodies. This type of immunity is long term.


B. CELLULAR IMMUNITY: Another way of establishing host resistance is through T-lymphocytes. These cells synthesize and release pharmacologically active substances ("lymphokines") which can kill cells carrying foreign Ags. T-lymphocytes also act against the invader by stimulation of macrophages. This activity of the immune system is known as cell mediated immunity. The peak of activity occurs around the tenth day.

Cell Mediated Immunity : 

Cell Mediated Immunity In cell mediated, the t-cells attach to foreign antigen cells and interact directly by cell to cell contact

Passive immunity : 

Passive immunity Immunity conferred by an antibody produced in another host. It may be acquired naturally or artificially (through an antibody-containing preparation).


PASSIVE IMMUNITY Antibodies (Y) are also found in breast milk. The antibodies received through passive immunity last only several weeks. While your immune system was developing, you were protected by immune defenses called antibodies. These antibodies traveled across the placenta from the maternal blood to the fetal blood.

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Passive Immunity occurs when the antibodies come from some other source. This type of immunity is short term.

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A. Humoral Immunity: This type of immunity is due to circulating Abs (Gamma - globulin's also called immunoglobulins). On stimulation, B-lymphocytes divide and its daughter cells are transformed into plasma-cells. The latter secrete the Abs into the circulation. An antibody is a protein produced in response to an antigen.

5 Types of Antibodies : 

5 Types of Antibodies Immunoglobulin G (IgG)—in plasma and tissue fluids; effective against virus, bacteria, & toxins; activate complement; babies get from mom through cord ?lasts 6 months to 1 yr Immunoglobulin A (IgA)—in exocrine gland secretions (sweat glands); breast milk, tears, nasal fluid, bile, urine, etc.

5 Types Antibodies…. : 

5 Types Antibodies…. Immunoglobulin M (IgM)—develops in response to bacteria Immunoglobulin D (IgD)—found on surfaces of B-cells; important to B-cell activation Immunoglobulin E (IgE)—in exocrine secretions along w IgA; ASSOCIATED WITH ALLERGIC REACTIONS

Antigens : 

Antigens Antigens are macromolecules that elicit an immune response in the body. The most common antigens are proteins and polysaccharides. Foreign substances that invade a host Substances that induce the formation of antibodies. Most are proteins or large polysaccharides from a foreign organism. On the surface of all cells.

Antigens : 

Antigens 4 phases associated with the immune response to an antigen: 1. Recognition of the invader 2. Amplification of the defenses (WBC) 3. Attack phase 4. Slowdown phase: number of defenders return to normal following the attack

Immunizing agents : 

Immunizing agents

Immunizing Agents : 

Immunizing Agents Vaccine: suspension of live or dead microorganism Toxoid: bacterial toxin that has been rendered nontoxic Immune globulin: sterile solution containing antibodies from human blood Antitoxin: solution of antibodies derived from the serum of animals immunized from specific antigens

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Vaccination and Immunization Vaccination and vaccine derive from vaccinia, the virus once used as smallpox vaccine. Thus, vaccination originally meant inoculation with vaccinia virus to render a person immune to smallpox.

Immunizations : 

Immunizations Immunization: process of inducing or providing immunity by administering an agent Active: production of an antibody in response to the administration of a vaccine Passive: temporary immunity by the administration of performed antibodies or antitoxins Agents used include: Ig’s and antitoxins

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Vaccination: A vaccination is an injection of a weakened form of the actual antigen that causes the disease. The injection is too weak to make you sick, but your B lymphocytes will recognize the antigen and react as if it were the "real thing". Thus, you produce MEMORY cells for long term immunity.

Live attenuated (avirulent) vaccines : 

Live attenuated (avirulent) vaccines Virulent pathogenic organisms are treated to become attenuated and avirulent but antigenic. They have lost their capacity to induce full-blown disease but retain their immunogenicity. Live attenuated vaccines should not be administered to persons with suppressed immune response due to: Leukemia and lymphoma Other malignancies Receiving corticosteroids and anti-metabolic agents Radiation pregnancy

Inactivated (killed) vaccines : 

Inactivated (killed) vaccines Organisms are killed or inactivated by heat or chemicals but remain antigenic. They are usually safe but less effective than live attenuated vaccines. The only absolute contraindication to their administration is a severe local or general reaction to a previous dose.

Polysaccharide and polypeptide (cellular fraction) vaccines : 

Polysaccharide and polypeptide (cellular fraction) vaccines They are prepared from extracted cellular fractions e.g. meningococcal vaccine from the polysaccharide antigen of the cell wall, the pneumococcal vaccine from the polysaccharide contained in the capsule of the organism, and hepatitis B polypeptide vaccine. Their efficacy and safety appear to be high.

Surface antigen (recombinant) vaccines. : 

Surface antigen (recombinant) vaccines. It is prepared by cloning HBsAg gene in yeast cells where it is expressed. HBsAg produced is then used for vaccine preparations. Their efficacy and safety also appear to be high.


HAZARDS OF IMMUNIZATION No immune response is entirely free from the risk of adverse reactions or remote squeal. The adverse reactions that may occur may be grouped under the following heads: Reactions inherent to inoculation Reactions due to faulty techniques Reactions due to hypersensitivity Neurological involvement Provocative reactions Others

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