Acquired Immunity PDF

Acquired immunity Dr/ Fahad Alzowahi Assistant professor in Microbiology  It is also known as adaptive immunity or specific immunity. It comprises the mechanisms that defend the host from infection in a specific manner. It is in contrast to innate immunity, because is not present at...

Acquired immunity Dr/ Fahad Alzowahi Assistant professor in Microbiology  It is also known as adaptive immunity or specific immunity. It comprises the mechanisms that defend the host from infection in a specific manner. It is in contrast to innate immunity, because is not present at birth. It is acquired after exposure to an antigen either by infection or vaccination (active immunity) or by the transfer of antibody or lymphocytes from an imm- une donor (passive immunity). Adaptive immunity displays four characteristic attributes which include; 1- Antigenic specificity: The immune system is complex and has evolved to protect the individual from harm. This harm may be either in the form of foreign pathogenic microorganisms or premalignant muta- tions in the individual’s own cells. To achieve this safely, the immune system must have the ability to distinguish self from non- self or altered-self to avoid damaging the host itself. The immune system has the potential for distinguishing among at least billion different antigen. Antibodies can distinguish between two protein molecules that differ in only a single amino acid. 2- Diversity: Immune response are specialized and different response are designed to be defend against different classes of microbes. 3- Immunologic memory: Once the immune system has recognized and responded to an antigen, it exhibits immunologic memory; that is, a second encounter with the same antigen induces a heighte- ned state of immune reactivity. Because of this attri- bute, the immune system can provides life-long immunity to many infectious agents after an initial encounter. The response to the first exposure to antigen, called the primary immune response, is mediated by lymphocyte, called naive lymphocyte.  Subsequent encounters with the same antigen lead to response, called secondary immune response, that are usually more rapid, larger and better able to eliminate the antigen than the primary immune response. Secondary immune response are result of the acti- vation of memory lymphocyte, which are long-lived cells that were induced during the primary immune response. Immunologic memory optimizes the ability of the immune system to combat (fight) persistent and recurrent infections, because each encounter with a microbe generates more memory cells and activates previously generates memory cells.  Memory is also one of the reason why vaccines confer long-lasting protection against infections. Antigen (figure 10). Fig. (10): Primary and secondary immune response. 4- Self/non self-recognition: The immune system normally responds only to foreign antigens, indicating that it is capable of self/nonself recognition (i.e. the ability of the immune system to distinguish self from nonself antigens. There are two types of acquired immunity are known as active and passive. Both active and passive immunity may be divided into natural and artificial. Natural immunity: acquired as part of normal life experiences. Artificial immunity: acquired through a medical procedure such as a vaccine or preformed antibodies. Active immunity: results when a person is exposed to Ag that stimulates production of Ab. It creates memory, takes time and is lasting. Passive immunity: preformed Ab are donated to an individual. It does not create memory, acts immediately, and is short term. Administration of antibody (antisera) against certain viruses (e.g., hepatitis B) can be useful during the incubation period to limit viral multiplic- ation, after a needle stick injury to someone who has not been vaccinated. Administration of antibody against diphtheria, tetanus, botulism, makes large amount of antitoxins immediately available to neutralize the toxins. Types of acquired immunity: 1- Natural active immunity: Immunity may be acquired naturally through contact with the specific disease organism (contact with foreign antigens as microorganisms), in which case, antibodies manufa- ctured by the infected person’s cells which act against the infecting agent or its toxins. 2- Artificial active immunity: acquired through inoculation with a selected Ag. Immunization with live attenuated or killed infectious agents, exposure to microbial products (e.g., toxins, toxoids). 3- Natural passive immunity: acquired by fetus through placenta as (IgG) and to newborn by milk from mother "human colostrum" as (IgA). 4- Artificial passive immunity: administration of immune serum or globulin (figure 11). Herd immunity: Also known as population immunity. Is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through previous infection. Fig.(11): Types of acquired immunity. Humoral immunity: Humoral immunity refers to immunity to pathogens by specific proteins called antibodies. After recognition of antigens by B lymphocytes (B-cells), they activate, proliferate, and differenti- ate into plasma cells to synthesize and secrete specific antibodies against these antigens. Cell-mediated immunity: It is an immune response that mediated by T- cells, phagocytes, and NK cells. It plays a major role in defending against fungi, protozoa, cancers, and intracellular bacteria. It also plays a major role in transplant rejection. Table(3): : Features of innate and acquired immunity.