Learning Outcomes:
i. Define specific immune defense and explain its role in the immune system's response to pathogens.
ii. Differentiate between cellular immunity and humoral immunity, the two main arms of specific immune defense.
iii. Describe the role of monocytes in antigen presentation and the initiation of specific immune responses.
iv. Explain the function of T lymphocytes (T cells) in cellular immunity, including their involvement in recognizing and destroying infected cells.
v. Discuss the role of B lymphocytes (B cells) in humoral immunity, including their production of antibodies that neutralize pathogens and promote their destruction.
vi. Recognize the significance of specific immune defense in providing long-lasting protection against infections.
i. Specific Immune Defense: A Tailored Response
The immune system employs two main arms of specific immune defense: cellular immunity and humoral immunity. Unlike innate immunity, which provides a non-specific response to a wide range of pathogens, specific immune defense is tailored to recognize and eliminate specific pathogens.
ii. Cellular Immunity: The Attackers
Cellular immunity involves the activation of T lymphocytes (T cells) to recognize and destroy infected cells. T cells are divided into two main types:
Killer T (Tc) cells: Tc cells directly attack and destroy infected cells, utilizing mechanisms such as perforin-mediated pore formation and death receptor activation.
Helper T (Th) cells: Th cells provide essential support for other immune cells, including Tc cells and B cells. They produce cytokines, signaling molecules that regulate immune responses.
iii. Antigen Presentation: The Spark of Immunity
Monocytes, which differentiate into macrophages or dendritic cells, play a crucial role in initiating specific immune responses:
Phagocytosis: Monocytes engulf pathogens and break them down into smaller fragments called antigens.
Antigen presentation: Monocytes migrate to lymphoid tissues, such as lymph nodes, and present antigens to T cells. This interaction activates T cells, priming them to recognize and respond to the specific pathogen.
iv. Humoral Immunity: The Neutralizers
Humoral immunity involves the production of antibodies by B lymphocytes (B cells). Antibodies are Y-shaped proteins that recognize and bind to specific antigens on pathogens:
Activation: Upon encountering an antigen, B cells are activated and undergo clonal expansion, producing a large number of identical daughter cells called plasma cells.
Antibody secretion: Plasma cells produce and secrete large amounts of antibodies specific to the antigen that triggered their activation.
Pathogen neutralization: Antibodies can neutralize pathogens by blocking their entry into cells or by marking them for destruction by phagocytes.
v. Long-lasting Protection: A Memory of Immunity
Specific immune defense provides long-lasting protection against infections:
Memory T cells: After an infection, a subset of T cells become memory T cells. These cells retain the ability to recognize and quickly respond to the same pathogen upon re-encounter.
Memory B cells: Similarly, a subset of B cells become memory B cells. These cells can rapidly produce antibodies specific to the pathogen they encountered previously.
Specific immune defense, with its cellular and humoral arms, is a sophisticated and highly effective mechanism for combating infections. By recognizing and eliminating specific pathogens, it provides long-lasting protection against future infections. Understanding the principles of specific immune defense highlights the remarkable adaptability and memory of the immune system in protecting the body from a wide range of threats.
