Antigen: An antigen is any substance that induces an immune response in the body, specifically the production of antibodies. Antigens can include pathogens such as bacteria and viruses, as well as non-infectious substances like pollen or food proteins.
Dual nature of the immune system: The most important dual nature of the immune system is that it consists of both innate (non-specific) and adaptive (specific) immunity. The innate response is immediate and acts against all pathogens, while the adaptive response is slower but tailored to specific pathogens and provides memory for future infections.
Definitions of key terms:
Antigen-specific: Refers to the ability of the immune response to specifically recognize and respond to distinct antigens.
Systemic: Indicates that the immune response is not limited to the site of infection but can affect the entire body.
Memory: The capability of the immune system to remember past infections and mount a faster response upon re-exposure to the same pathogen.
Self/non-self recognition: Self/non-self recognition is achieved through the presentation of antigens by Major Histocompatibility Complex (MHC) molecules, allowing immune cells to distinguish between the body's own cells and foreign invaders.
Types of Leukocytes: The five types of leukocytes (white blood cells) are:
Neutrophils
Lymphocytes
Monocytes
Eosinophils
Basophils
The Lymph System
Lymph: Lymph is a clear fluid that circulates within the lymphatic system, similar to blood plasma, and originates from interstitial fluid in tissues.
Functions of lymph: Lymph functions by transporting excess interstitial fluid back to the bloodstream, absorbing dietary fats from the intestine, and providing a conduit for immune cells to travel throughout the body.
Role of lymph nodes: The role of lymph nodes is to filter lymph and trap pathogens and foreign particles, allowing immune cells to mount a response against them.
Types of lymphoid organs: The human lymphoid system consists of two types of organs:
Primary lymphoid organs (e.g., bone marrow, thymus) - where lymphocytes are produced and mature.
Secondary lymphoid organs (e.g., lymph nodes, spleen) - where immune responses are initiated.
Innate Immunity
Innate immunity system: The innate immunity system is the body's first line of defense, providing immediate but non-specific protection against pathogens through physical barriers, chemical barriers, and immune responses.
Most important barrier: The most important barrier of innate immunity is the skin, which acts as a physical barrier preventing pathogen entry.
Normal flora (Bacteria): Normal flora refers to the microorganisms that reside on and within the human body, playing a crucial role in maintaining health by outcompeting harmful pathogens and supporting immune function.
Phagocyte: A phagocyte is a type of immune cell that engulfs and digests pathogens and debris through a process known as phagocytosis.
Macrophages: Macrophages are large phagocytic cells derived from monocytes that are found throughout the body in tissues, playing a vital role in detecting, engulfing, and destroying pathogens and initiating immune responses.
Function of Natural Killer Cells: The function of Natural Killer (NK) cells is to identify and destroy infected or cancerous cells by releasing cytotoxic substances that induce apoptosis (programmed cell death).
Adaptive or Acquired Immunity
Types of Lymphocytes: Lymphocytes come in two major types:
B cells
T cells
B cells: B cells are produced in the stem cells of the bone marrow and are responsible for producing antibodies in response to antigens.
B cells' involvement: B cells are involved in humoral immunity, which is mediated by antibodies produced against specific antigens.
T cells: T cells are non-antibody-producing lymphocytes that are also produced in the bone marrow but mature in the thymus. They play a central role in cell-mediated immunity.
T cells' involvement: T cells are involved in recognizing and responding to infected cells, tumor cells, and coordinating the immune response through signaling mechanisms.
Cell-mediated Immunity
Overall function: Generally speaking, cell-mediated immunity works by activating T cells that directly attack infected cells or provide help to other immune cells.
Cytotoxic T cells: Cytotoxic or killer T cells do their work by releasing perforin and granzymes, which induce apoptosis in infected cells.
Helper T cells: Helper T cells serve as a regulatory unit that helps activate B cells, cytotoxic T cells, and macrophages by releasing signaling molecules called cytokines.
Helper T cells' function: Helper T cells work by recognizing antigens presented by antigen-presenting cells and then stimulating other immune cells to respond effectively.
Role of Lymphokines: The role of lymphokines is to act as signaling molecules that mediate communication between T cells and other cells in the immune response.
Role of Suppressor T Cells: The role of Suppressor T cells (regulatory T cells) is to downregulate the immune response after an infection has been cleared to maintain immune homeostasis.
Role of Memory T Cells: The role of Memory T cells is to persist long-term after an infection has been resolved and respond rapidly upon re-exposure to the same antigen, leading to a quicker and more effective immune response.
Humoral Immunity
Immunocompetency: Immunocompetency is defined as the ability of the immune system to recognize and respond to specific antigens effectively, leading to the formation of immune memory.
Sensitization of B-lymphocytes: When B-lymphocytes are sensitized to an antigen with the help of a Helper T cell, they undergo clonal selection and differentiation into plasma cells that produce antibodies specific to that antigen.
Antibodies: Antibodies are also called immunoglobulins and are glycoproteins produced by B cells that specifically bind to antigens to neutralize or mark them for destruction.
Types of Antibodies: The five types of antibodies are:
IgG
IgA
IgM
IgE
IgD
Interaction of T cells and B cells with Antigens: The interaction process involves T cells assisting in the activation of B cells. Helper T cells recognize the antigen presented by B cells, releasing cytokines that stimulate B cell proliferation and differentiation into antibody-secreting plasma cells.
Goal of all Vaccines: The goal of all vaccines is to stimulate the immune system to develop long-lasting immunity against a specific pathogen, often by eliciting a primary immune response without causing the disease.
Secondary Immune Response: A secondary immune response is a more rapid and robust immune response that occurs upon re-exposure to a previously encountered antigen, due to the presence of memory cells that recognize the antigen.
Summary
Types of Immunity: Immunity can be categorized into several types:
Natural immunity: Acquired through natural exposure to pathogens or from maternal antibodies.
Artificial immunity: Obtained through medical interventions such as vaccines or immunotherapy.
Innate immunity: The defense mechanisms that are present at birth and provide immediate, non-specific protection.
Acquired/adaptive immunity: Develops over time through exposure to specific pathogens and involves the formation of memory for future responses.
Active immunity: Developed through engagement of the immune system with an antigen, leading to the production of antibodies.
Passive immunity: Provides immediate but temporary protection through the transfer of antibodies from one individual to another, such as maternal antibodies to infants.