Dr Abdul Ghaffar

VIDEO LECTURE

 
 IMMUNOLOGY - CHAPTER   FOURTEEN 

  IMMUNIZATION 
 

TEACHING OBJECTIVES
Know the distinction between passive and active immunization and their examples
Distinguish between artificial and natural means of immunization
Know the applications and problems of artificial passive immunization
Know the applications and problems of artificial active immunization
Know the modern approaches to immunization

Immunization is the means of providing specific protection against most common and damaging pathogens. Specific immunity can be acquired either by passive or by active immunization and both modes of immunization can occur by natural or artificial means (figure 1).

Passive Immunity

Immunity can be acquired, without the immune system being challenged with an antigen. This is done by transfer of serum or gamma-globulins from an immune donor to a non-immune individual. Alternatively, immune cells from an immunized individual may be used to transfer immunity. Passive immunity may be acquired naturally or artificially.

Naturally acquired passive immunity
Immunity is transferred from mother to fetus through placental transfer of IgG or colostral transfer of IgA.

Artificially acquired passive immunity
Immunity is often artificially transferred by injection with gamma-globulins from other individuals or gamma-globulin from an immune animal. Passive transfer of immunity with immune globulins or gamma-globulins is practiced in numerous acute situations of infections (diphtheria, tetanus, measles, rabies, etc.), poisoning (insects, reptiles, botulism), and as a prophylactic measure (hypogammaglobulinemia). In these situations, gamma-globulins of human origin are preferable although specific antibodies raised in other species are effective and used in some cases (poisoning, diphtheria, tetanus, gas gangrene, botulism). While this form of immunization has the advantage of providing immediate protection, heterologous gamma-globulins are effective for only a short duration and often result in pathological complications (serum sickness) and anaphylaxis. Homologous immunoglobulins carry the risk of transmitting hepatitis and HIV.

Passive transfer of cell-mediated immunity can also be accomplished in certain diseases (cancer, immunodeficiency). However, it is difficult to find histocompatible (matched) donors and there is severe risk of graft versus host disease.

See also Virology Chapter "Vaccines" in this On-line Textbook

  
Figure 1A. Edward Jenner carries out a vaccination

  B. Pre and post vaccine incidence of common infectious diseases

  C. Modes of immunization

D. Milestones of immunization

Figure 2  Introduction of variolation

Figure 3 
Live attenuated vaccines

Figure 4 Killed whole organism vaccines

 
  Figure 5
Microbial fragment vaccines

  Figure 6 Modification of toxin to toxoid

Figure 7  Advantages and disadvantages of passive immunization

Active Immunity

This refers to immunity produced by the body following exposure to antigens.

Naturally acquired active immunity
Exposure to different pathogens leads to sub-clinical or clinical infections which result in a protective immune response against these pathogens.

Artificially acquired active immunity
Immunization may be achieved by administering live or dead pathogens or their components. Vaccines used for active immunization consist of live (attenuated) organisms, killed whole organisms, microbial components or secreted toxins (which have been detoxified). 

The first live vaccine was cowpox virus introduced by Edward Jenner as a vaccine for smallpox (see vaccine section); however, variolation,  innoculation using pus from a patient with a mild case of smallpox has been in use for over a thousand years (figure 2)

Live vaccines are used against a number of viral infections (polio (Sabin vaccine), measles, mumps, rubella, chicken pox, hepatitis A, yellow fever, etc.) (figure 3). The only example of live bacterial vaccine is one against tuberculosis (Mycobacterium bovis: BCG). While live vaccines normally produce only self-limiting non-clinical infections and subsequent immunity, they carry a serious risk of causing overt disease in immunocompromised individuals. Killed (heat, chemical or UV irradiation) viral vaccines include those for polio (Salk vaccine), influenza, rabies, influenza, rabies, etc. Most bacterial vaccines are killed organisms ( typhoid, cholera, plague, pertussis, etc.) (figure 4). Other bacterial vaccines utilize their cell wall components (haemophilus, pertussis, meningococcus, pneumococcus, etc.) (figure 5). Some viral vaccines (hepatitis-B, rabies, etc.) consist of antigenic proteins cloned into a suitable vector (e.g., yeast). When the pathogenic mechanism of an agent involves a toxin, a modified form of the toxin (toxoid) is used as a vaccine (e.g., diphtheria, tetanus, cholera) (figure 6). These subunit vaccines are designed to reduce the toxicity problems. Each type of vaccine has its own advantages and disadvantages (figure 7).

Anti-idiotype antibodies are also under trial. Similarly, DNA vaccines and immunodominant peptides (recognized by the MHC molecules) are under investigation, particularly for protection against viral diseases.

The protective immunity conferred by a vaccine may be lifelong (measles, mumps, rubella, small pox, tuberculosis, yellow fever, etc.) or may last as little as six months (cholera). 

The primary immunization may be given at the age of 2 - 3 months (diphtheria, pertussis, tetanus, polio), or 13 - 15 months (mumps, measles, rubella). Recommended schedules are summarized in table 1. A number of other vaccines are licensed for use in the US and are recommended for individuals or groups at risk.

Active immunization may cause fever, malaise and discomfort. Some vaccine may also cause joint pains or arthritis (rubella), convulsions, sometimes fatal (pertussis), or neurological disorders (influenza). Allergies to eggs may develop as a consequence of viral vaccines produced in eggs (measles, mumps, influenza, yellow fever). Table 2 summarizes frequencies of undesirable effects of diphtheria-tetanus-polio (DTP) vaccine.

You have learned: 

Different modes of acquiring immunity

Which mode is used or applicable in what situation

Advantages and disadvantages of different modes of immunization

Rationale for vaccine design

Risk and benefits of vaccination

Return to the Department of Pathology, Microbiology and Immunology

Return to the Immunology Section of Microbiology and Immunology On-line

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