Acquired Immunity (Adaptive Immunity): Active Immunity

Acquired immunity, also known as adaptive immunity, refers to the resistance developed by individuals throughout their lifetime against infections.

Unlike innate immunity, which is present from birth, acquired immunity is not inherited from parents but acquired through exposure to specific antigens.
This specific immunity allows humans to adapt better to their environment, providing enhanced protection against pathogens and diseases.

In this comprehensive article, we will delve into the intricacies of acquired immunity, its types, and how they contribute to strengthening the body’s defense mechanism.

Understanding Acquired Immunity

Acquired immunity is characterized by its specificity, as it is triggered by particular antigens.
These antigens can be proteins, carbohydrates, or other molecules present on the surface of pathogens, such as bacteria, viruses, or parasites.

When these antigens enter the body, they are recognized by the immune system, initiating a series of complex immune responses.

Acquired immunity can be broadly classified into two types:
1. Active immunity

2. Passive immunity.
Both types can be further categorized as natural or artificial based on their origin.

Active Immunity:

Natural Active Immunity

Natural active immunity occurs when a person develops resistance after being infected by a specific pathogen.

For example, when an individual recovers from diseases like measles or smallpox, they acquire natural active immunity against those specific infections.
In many cases, natural active immunity can provide lifelong protection, as seen in certain viral infections like smallpox, measles, and mumps.
However, the duration of immunity varies depending on the pathogen.

Bacterial infections often confer less permanent immunity compared to viral infections. For instance, diseases like bacillary dysentery and influenza may provide only short-lived immunity.
Additionally, the common cold, caused by various viruses, can lead to an apparent lack of immunity as different strains of the virus can cause repeated infections.

Artificial Active Immunity

Artificial active immunity is achieved through the administration of vaccines.

Vaccines are preparations containing either weakened or inactivated forms of pathogens or their specific antigens.
By introducing these antigens into the body, vaccines stimulate the immune system to produce a protective immune response without causing the disease itself.

Live Vaccines – Attenuated Vaccines

Live vaccines, also known as attenuated vaccines, contain live microorganisms that have been weakened or attenuated.

These vaccines closely mimic natural infections, producing an immune response similar to that of a natural infection, albeit at a lower level. The resulting immunity can last for several years, although booster doses may be necessary in some cases.

Examples of live vaccines include:

Anthrax Vaccine: Bacilli causing anthrax are attenuated by growing them at specific temperatures.

BCG (Bacille Calmette Guerin) Vaccine: Used for tuberculosis immunization, the bacilli are attenuated by cultivation in a glycerol-bile-potato medium.
Sabin Vaccine (Oral Poliomyelitis Vaccine): Contains live attenuated strains of poliomyelitis virus and is administered orally.
Measles Vaccine: Utilizes an attenuated measles virus and is given to immunize children against measles.

Killed Vaccines

Killed vaccines consist of microorganisms that have been inactivated through heat or chemicals while retaining their antigenic properties.
These vaccines are generally less immunogenic compared to live vaccines and may require repeated administration or booster doses.

Examples of killed viral vaccines include:

Salk Vaccine: Prepared from formalin-killed poliovirus and administered through subcutaneous injections.
Influenza Virus Vaccine: Contains formalin-killed influenza virus and provides short-lived immunity, lasting approximately six months.

Examples of killed bacterial vaccines include:

TAB Vaccine: Heat-killed, phenol-preserved bacterial vaccine used for enteric fevers (typhoid and paratyphoid).
Pertussis Vaccine: Contains formalin-killed virulent strains of bacteria causing whooping cough. Often given in combination with diphtheria toxoid and tetanus toxoid.

Toxoid Vaccines

Toxoid vaccines utilize inactivated toxins (products of microorganisms) to induce the production of antitoxins.

These vaccines are prepared by treating bacterial toxins with formalin, retaining their antigenic potency while eliminating their harmful effects.

Examples of toxoid vaccines include:

Tetanus Toxoid: Prepared from formaldehyde-detoxified tetanus toxin and used for immunization against tetanus.

Diphtheria Toxoid: Produced by formalin treatment of the bacterial toxin responsible for diphtheria. Commonly administered as part of the triple vaccine.
Triple Vaccine (DPT): A combination vaccine containing diphtheria toxoid, tetanus toxoid, and pertussis vaccine. Routinely used to induce active immunity against diphtheria, tetanus, and whooping cough in children.

Vaccination Schedules

Vaccination schedules outline the recommended timing and sequence of vaccine doses.

They are developed by government agencies and physician groups to ensure optimal immune response and long-term protection against infectious diseases.
These schedules vary from country to country based on factors such as local disease prevalence, age groups, and risk factors.
Many vaccines require multiple doses to establish adequate immunity.

The initial dose, known as the primary dose, is often followed by booster doses to reinforce and maintain the immune response.
Adhering to vaccination schedules is crucial to achieve maximum protection against targeted pathogens.

A Vital Tool for Disease Prevention

Acquired immunity plays a pivotal role in protecting individuals from various infectious diseases. Whether acquired naturally or through vaccination, active immunity empowers the immune system to recognize and eliminate specific pathogens.

This heightened defense mechanism helps prevent the spread of diseases and contributes to public health on a global scale.
By understanding the different types of acquired immunity and the significance of vaccination, individuals can make informed decisions about their own health and contribute to collective efforts in disease prevention.

Conclusion

Acquired immunity, with its active and passive components, provides individuals with the ability to combat specific pathogens and diseases. Whether through natural infections or artificial means such as vaccination, the immune system becomes fortified against targeted antigens, enhancing the body’s defense mechanism. Adhering to vaccination schedules and understanding the types of acquired immunity are essential for individuals to protect themselves and contribute to disease prevention efforts.

FAQs

Q1: How long does natural active immunity last?

Natural active immunity can provide lifelong protection against certain infections, such as measles and smallpox. However, the duration of immunity varies depending on the pathogen and individual factors.

Q2: Can vaccines provide lifelong immunity?

While some vaccines, like those for measles and mumps, can offer long-lasting immunity, others may require booster doses to maintain protection. The duration of immunity depends on the vaccine and the individual’s response.

Q3: Are live vaccines more effective than killed vaccines?

Live vaccines, by closely mimicking natural infections, often provide stronger and longer-lasting immunity. However, killed vaccines still confer significant protection and are necessary for certain pathogens.

Q4: Why do vaccination schedules vary between countries?

Vaccination schedules are tailored to local disease prevalence, risk factors, and healthcare infrastructure. They are designed to maximize the immune response and provide optimal protection for the population.

Q5: How does acquired immunity contribute to public health?

Acquired immunity, whether acquired naturally or through vaccination, helps prevent the spread of infectious diseases. By enhancing the body’s defense mechanism, acquired immunity reduces the overall burden of diseases and promotes public health on a global scale.