Introduction

Immunity is the body's defense mechanism against foreign pathogens, such as viruses, bacteria, and parasites. This defense can be innate or adaptive, with adaptive immunity being further divided into active and passive immunization. This course will delve into the intricacies of passive and active immunization in detail.

Adaptive Immunity: An Overview

Adaptive immunity is a specific response that targets foreign pathogens, offering long-lasting protection against reinfection. It is composed of two types: humoral immunity (antibody mediated) and cell-mediated immunity. This course will focus on the mechanisms of passive and active immunization, both belonging to the humoral immunity branch.

Antigens

Antigens are substances present on the surface of pathogens that trigger an immune response. They bind to specific receptors (antigen-specific receptors) on lymphocytes, inducing their activation and differentiation into effector cells.

Passive Immunization

Passive immunization is a form of protection in which preformed antibodies are transferred from an immune individual to a non-immune individual. This transfer can be achieved through the administration of immune serum or immunoglobulin preparations, such as:

Immune Serum

Immune serum is the liquid portion of blood containing antibodies produced in response to an antigenic challenge. It provides temporary protection against a specific pathogen for a few weeks to months, depending on the half-life of the transferred antibodies.

Immunoglobulin Preparations

Immunoglobulin preparations are purified from immune serum and are available in various forms, such as:

1. Intravenous immunoglobulin (IVIG)
2. Intramuscular immunoglobulin (IMIG)
3. Subcutaneous immunoglobulin (SCIG)
   These preparations offer longer-lasting protection than immune serum due to their higher antibody concentration and improved retention time in the body.

Indications for Passive Immunization

Passive immunization is used primarily in situations where active immunization is not possible or not desirable, such as:

1. Immediate protection against a specific pathogen during an outbreak (e.g., tetanus toxoid for wound management)
2. Prophylaxis and treatment of diseases in high-risk individuals (e.g., immune deficiency disorders)
3. Protection of newborns who have not yet developed their own immunity (e.g., passive transfer of antibodies from mother to child)
4. Emergency situations, such as exposure to a potentially lethal dose of a pathogen or toxin (e.g., antivenom for snake bites)

Active Immunization

Active immunization is a process in which an individual's immune system is stimulated to produce its own antibodies against a specific pathogen. This is achieved through the administration of vaccines, which contain either weakened or inactivated pathogens or their antigenic components. Active immunization offers long-lasting protection and provides the body with an active memory response, allowing for a rapid recall of immune cells upon future exposure to the same pathogen.

Vaccines

Vaccines are preparations that contain either:

1. Live attenuated (weakened) viruses or bacteria
2. Inactivated (killed) viruses or bacteria
3. Subunit vaccines, consisting of specific antigenic components of a pathogen (e.g., hemagglutinin from the influenza virus)
   Vaccines stimulate an immune response by mimicking an infection without causing actual illness. The immune system recognizes the vaccine as foreign and mounts a defense against it, leading to the production of memory cells that can rapidly respond to future infections with the same pathogen.

Indications for Active Immunization

Active immunization is used primarily for the prevention of infectious diseases, such as:

1. Smallpox
2. Polio
3. Measles
4. Mumps
5. Rubella (German measles)
6. Tetanus
7. Diphtheria
8. Pertussis (whooping cough)
9. Hepatitis B
10. Influenza
11. Human papillomavirus (HPV)
12. Many others

Conclusion

Understanding the mechanisms of passive and active immunization is crucial for the development of effective strategies to prevent and treat infectious diseases. Passive immunization provides temporary protection through preformed antibodies, while active immunization offers long-lasting protection by stimulating the individual's immune system to produce its own antibodies.