Elements of the Host Protective Response (Part 1) Flashcards
Immunology
- Study of the immune system and its response to invading pathogens
Immune system
- The molecules, cells, tissues and organs that collectively function to provide immunity, or protection, against infectious pathogens
Immunity
- Resistance to disease, specifically infectious disease
Immune response
- A collective and coordinated response to the introduction of foreign substances in an individual
- Mediated by the cells and molecules of the immune system
Initial defense mechanisms are barriers
- Skin
- Acid and bile of the gastrointestinal tract
- Mucus at entry sites that inactivate and prevent entry of the foreign agents
Innate immunity (nonspecific)
- Mediates the initial protection against infections
- Relies on mechanisms that exist before infection
- Capable of rapid responses to microbes, and react in essentially the same way to repeat infections
Adaptive immunity (specific)
- Develops more slowly
- Mediated by lymphocytes and is stimulated by exposure to infectious agents
Innate immune system
- Also called natural or native immunity
- Always present in healthy individuals
- Prepared to block the entry of microbes and rapidly eliminate microbes that succeed in entering tissues
Epithelial barriers
- Prevent infections
Soluble factors and stimulators (innate immune system)
- Interferon
- Cytokines
- Chemokines
Cellular component (innate immune system)
- Eliminate microbes
- Natural killer cells, neutrophils & macrophages
Cytokines
- Hormone-like proteins that regulate immune responses
Interferons
- Proteins produced in response to viral and other infections
Chemokines
- Smaller proteins that are also regulatory for the immune system
Adaptive immune system
- Also called specific or acquired immunity
- Stimulated by microbes that invade tissues
- Adapts to the presence of microbial invaders
Adaptive immunity is characterized by
- Specificity for distinct macromolecules
- Memory (ability to respond more vigorously to repeated exposures to the same microbe)
Stem cell
- An undifferentiated cell that divides continuously
- Gives rise to additional stem cells and to cells of multiple lineages; “colony-forming unit
Stem cells reside primarily in
- Bone marrow
- Can also be isolated from the fetal blood in umbilical cords
- Rare in adult blood
Differentiation of stem cells into functional blood cells is triggered by
- Specific cell surface interactions with the stromal cells of the marrow
- Specific cytokines produced by these and other cells
Differentiation of a common progenitor cell
- The pluripotent stem cell
- Gives rise to all blood cells
Pluripotent stem cell (progenitor cell)
- Undifferentiated bone marrow cell that gives rise to the cells of the lymphoid, myeloid and erythrocytic lineages
Cell differentiation
- Acquirement of functions different from those of the original cell type
Distinguishing types of white blood cells
- Morphology & histologic staining
- Immunologic functions
- Intracellular & cell surface markers
Cluster of differentation (CD)
- Markers used to define white blood cell type
Class I major histocompatibility complex (MHC) antigens
- All nucleated cells express MHC I antigens
- MCH I recognizes self from non-self
Primary lymphoid organs
- Generative lymphoid organs
- Sites of initial lymphocyte differentiation
- Essential to the development of the immune system
Primary lymphoid organs (names)
- Bone marrow
- Thymus
Bone marrow
- Central cavity of bone is the site of generation of all circulating blood cells in the adult
- Site of B cell maturation
Thymus
- A bilobed organ situated in the anterior mediastinum
- Site of maturation of T lymphocytes from bone marrow-derived precursors
Secondary lymphoid organs
- Peripheral lymphoid organs
- Places where dendritic cells and B and T lymphocytes reside and respond to antigenic challenges
Secondary lymphoid organs (names)
- Lymph nodes
- Spleen
- Mucosa-associated lymphoid tissue (MALT)
- Gut-associated lymphoid tissue (Peyer’s patches)
- Bronchus-associated lymphoid tissue (tonsils, appendix)
Swollen glands
- Proliferation of the lymphocytes in response to infectious challenge causes these tissues to swell
Cells of the primary and secondary lymphoid organs express
- Cell surface adhesion molecules
- Interact with homing receptors expressed on B and T cells
Spleen and lymph nodes
- Encapsulated organs in which the macrophages and B and T cells reside in defined regions
- Promote development of adaptive immune responses
Spleen and lymph node location significance
- Facilitates interactions that promote immune responses to antigen
Lymph nodes
- Site where immune response is initiated
- Located along lymphatic channels throughout the body
- Antigen capture and transport system
Lymph
- Fluid from all epithelia and connective tissues is drained by lymphatics
- Transport the fluid (lymph) from the tissues to the lymph nodes
Antigen presenting cells (APCs)
- Located in the lymph nodes
- Sample the antigens of microbes that may enter through epithelia into tissues
Swollen lymph nodes
- Denotes stimulation of immunity and cell growth
3 layers of the lymph node
- Cortex
- Paracortex
- Medulla
Lymph node cortex
- Outer layer
- Contains mainly B cells, follicular dendritic cells & macrophages arranged in clusters (follicles)
Lymph node paracortex
- Contains dendritic cells that bring antigens from the tissues to be presented to the T cells to initiate immune responses
Lymph node medulla
- Contains B and T cells and antibody-producing plasma cells
Spleen
- Large abdominal organ that acts like a lymph node
- Site of immune responses to antigens in blood
Spleen functions
- Filters antigens, encapsulated bacteria, and viruses from blood
- Removes aged blood cells and platelets
Spleen structure
- Consists of 2 types of tissue, the white pulp and the red pulp
White pulp of the spleen
- Consists of arterioles surrounded by lymphoid cells (periarteriolar lymphoid sheath) in which the T cells surround the central arteriole
B cells of the white pulp
- Organized into primary unstimulated or secondary stimulated follicles that have a germinal center
Germinal center of the white pulp contains
- Memory cells
- Macrophages
- Follicular dendritic cells
Red pulp of the spleen
- Storage site for blood cells
- Site of turnover of aged platelets and erythrocytes
Cutaneous and mucosal associated lymphoid systems
- Under the epithelia of the skin
- Gastrointestinal and respiratory tracts
- Sites of immune responses to antigens that breach the epithelia
At any time, more than half of the body’s lymphocytes are in
- Mucosal tissues
- Many of these are memory cells
Mucosa associated lymphoid tissue (MALT)
- Peyer’s pathches
- Tonsils
- Lymphoepithelial organs
Tonsils
- Contain large number of mature and memory B cells
- Use their antibodies to sense specific pathogens
- Work with dendritic cells and T cells to initiate immune responses
Swelling of the tonsils
- May be caused by infection or a response to infection
Peyer’s patches
- Special cells in the epithelium (M cells)
- Deliver antigens to the lymphocytes contained in defined regions T [interfollicular] and B [germinal]
Lymphoepithelial organs
- Sample the microbes in the oral and nasal area
