Immunology Overview 8/26 Flashcards
Innate vs. Adaptive Immunity
- Innate immunity = also called natural immunity or native immunity, is prepared to block the entry of microbes and rapidly eliminate microbes that do succeed in entering host tissues.
- epithelial barriers
- phagocytes
- dendritic cells
- NK cells
- Complement proteins and cytokines
Adaptive immunity - (specific immunity or acquired immunity) requires expansion and differentiation of lymphocytes in response to microbes before it can provide effective defense; it adapts to the presence of microbial invaders.
- B lymphocytes and Antibodies produced
- T lymphocytes and Effector T cells
the mechanisms of innate immunity recognize structures shared by classes of microbes, the cells of adaptive immunity (lymphocytes) express receptors that specifically recognize a much wider variety of molecules produced by microbes as well as noninfectious substances. These substances are called antigens.
Cellular vs. Humoral Immunity
Humoral immunity = mediated by antibodies, which are produced by B lymphocytes. Antibodies are secreted into the circulation and mucosal fluids, and they neutralize and eliminate microbes and microbial toxins that are present outside of host cells, in the blood and in the lumens of mucosal organs.
Cellular Immunity = Defense against such intracellular microbes, is mediated by T lymphocytes. 1. eliminate phagocytosed microbes 2. kill any type of host cells that are harboring infectious microbes in the cytoplasm.
Thus, the antibodies produced by B lymphocytes recognize extracellular microbial antigens, whereas T lymphocytes recognize antigens produced by intracellular microbes.
Most T cells recognize only protein antigens, whereas B cells and antibodies are able to recognize many different types of molecules, including proteins, carbohydrates, nucleic acids, and lipids.
Active and Passive Immunity
Active Immunity = induced in an individual by infection or vaccination
Passive Immunity = conferred to an individual by transfer of antibodies or lymphocytes from an actively immunized individual. For the lifetime of the transferred antibodies or cells, the recipient is able to combat the infection.
- Passive immunity is useful for rapidly conferring immunity even before the individual is able to mount an active response
- it does not induce long-lived resistance to the infection
- ex. newborns
Properties of Adaptive Immune Responses
- specificity: ensures that distinct antigens elicit responses that target those antigens
- Diversity: enables immune system to respond to a large variety of antigens
- Memory: leads to rapid and enhanced responses to repeated exposures
- clonal expansion: increases number of antigen-specific lymphocytes to keep pace with microbes
- Specialization: Generates responses that are optimal for defense against different types of microbes
- Contraction and homeostasis: allows immune system to respond to newly encountered antigens
- Nonreactivity to self: prevents injury to the host during responses to foreign antigens
Natural vs. artificial immunity
- both are part of adaptive immunity:
- Natural is either passive (maternal) or active (infection)
- Artificial is passive (antibody transfer) or active (immunization)
Primary and secondary (memory) responses
Primary Response= The response to the first exposure to antigen - is mediated by lymphocytes called naive lymphocytes that are seeing antigen for the first time
Secondary Response: Subsequent encounters with the same antigen lead to immune responses that usually are more rapid, larger, and better able to eliminate the antigen than primary responses. Secondary responses are the result of the activation of memory lymphocytes, which are long-lived cells that were induced during the primary immune response.
Neutrophil
(PMN’s, polys) = primary responder ~ few hours
Neutrophils are a type of phagocyte and are normally found in the blood stream. During the beginning (acute) phase of inflammation, particularly as a result of bacterial infection, environmental exposure, and some cancers
neutrophils are one of the first-responders of inflammatory cells to migrate towards the site of inflammation.
Macrophage (MO)
- Antigen-presenting cell
- efffector phase of cell-mediated immunity
- cell of the mononuclear phagocyte system: respond to sites of inflammation in 1-2 days, but survive longer than Neutrophils
- Their role is to phagocytose, or engulf and then digest, cellular debris and pathogens, either as stationary or as mobile cells. They also stimulate lymphocytes and other immune cells to respond to pathogens. They are specialized phagocytic cells that attack foreign substances, infectious microbes and cancer cells through destruction and ingestion.
Natural Killer (NK)
Lymphocyte
- cells of innate immunity: recognize infected, stressed or malignant cells and kill them
Dendritic Cell (DC)
Antigen Presenting Cells: APC’s Located in the epithelium of skin, GI and respiratory tract that capture antigens and transport them to peripheral lympoid tissues and display them to lymphocytes
- Amoeboid cells, pick-upantigen and process
- bridge between innate and adaptive immunity!
B Cell
- lymphocytes that mature in bone marrow
- mediators of humoral immunity
- B cells express membrane forms of antibodies that serve as the receptors that recognize antigens and initiate the process of activation of the cells. Soluble antigens and antigens on the surface of microbes and other cells may bind to these B lymphocyte antigen receptors, initiating the process of B cell activation. This leads to the secretion of soluble forms of antibodies with the same antigen specificity as the membrane receptors.
T Cell
- Lymphocytes that mature in the thymus
- mediators of cell-mediated immunity
- antigen receptors recognize only peptide fragments of protein antigens that are bound to specialized peptide display molecules called major histocompatibility complex (MHC) molecules on the surface of antigen-presenting cells
CD4 + T cells = helper T cells because they help B lymphocytes to produce antibodies and help phagocytes to destroy ingested microbes.
CD8 + T lymphocytes = cytotoxic T lymphocytes (CTLs) because they kill cells harboring intracellular microbes.
Regulatory T cells: special subset of CD4 + T cells that functions to prevent or limit immune responses;
