The Immune/Lymphoid System Flashcards
What are the functions of the protective surface inmmune system mechanism?
- first line of defense in skin and mucous membranes
- protected by a variety of antibacterial substances including defensins and lysozymes (in tears and saliva)
What are the three main lines of defense for humans?
- protective surface mechanisms
- innate immune system
- adaptive immune system
What are the functions of the innate immune system?
- rapid reaction to a pathogen
- same magnitude of reaction with each encounter (no learning)
- cells, proteins, peptides that circulate in the blood
- many of the same cells and signaling molecules used in innate are vital in the adaptive as well
What are the characteristics of acute inflammation?
- vascular changes including dilation, enhanced permeability of capillaries, and increased blood flow
- production of fibrin-rich inflammatory exudate
What are the functions of the adaptive immune system?
- ability to learn so that the subsequent response elicits a greater, more specific, faster response
- uses T and B lymphocytes
- requires antigen-representing cells
What are the actions of the neutrophil, eosinophil, and macrophage?
Phagocytosis and killing of pathogenic organisms
Secretion of cytokines and extracellular antimicrobial
molecules, including neutrophil extracellular traps
(NETs) and pattern recognition molecules (PRMs)
What are the actions of the complement and chemokines?
Opsonises organisms to facilitate phagocytosis
Chemoattractant for various cells
Membrane attack complex (MAC) kills cells by
puncturing plasma membrane
What are the actions of the natural killer (NK) cells?
Recognize and kill virus-infected and cancerous cells
What are the dense lymphoid tissues?
- organized into discreet structures or organs (lymph nodes, spleen, thymus, tonsil)
What are the diffuse lymphoid tissues?
—located throughout body, associated with mucous membranes
What is primary lymphoid tissue?
— lymphoid tissue where b- & t-cells acquire surface receptors
— bone marrow for b cells and thymus for t cells
What is the secondary lymphoid tissue?
Mature b- & t-cells secondarily migrate to all other lymphoid tissue
What are malignant tumors of the immune system called when they involve a solid organ?
lymphomas
What are malignant tumors of the immune system called when they involve blood?
leukemias
What do lymphatic vessels allow for?
- route which allows cells and large molecules in ECM to re-enter the bloodstream
- assist circulation of lymphocytes
- concentrate antigens for elimination within lymph nodes
What activates a lymphocyte?
antigen binds to their surface receptor
What cell constantly patrols the body, circulates in blood,
lymph and extracellular fluid, and pauses in organized
lymphoid tissue?
lymphocytes
What does the binding of B cell receptors depend on?
shape and electrical charge
What does binding to T cell receptors require?
shape, electrical charge, and must bind to the major histocompatibility complex (MHC)
What are the roles of T-lymphocytes?
- T helper cells (TH cells) - ‘help’ other cells to perform their effector functions by secreting a variety of mediators
- Cytotoxic T cells (TC cells) - kill virus-infected and some cancer cells. They require interaction with TH cells to become activated and proliferate to form clones
- Regulatory T cells (TREG) - suppress immune responsiveness to self-antigens (autoimmunity) and switch off the response when antigen is removed
- Memory T cells - develop from activated T cells to provide a ‘rapid reaction force’ for a subsequent encounter with the same antigen
Which T cell s ‘help’ other cells to perform their effector functions by secreting a variety of mediators? TH cells thus provide ‘help’ to B cells, cytotoxic T cells and macrophages.
T helper cell
What T cells s are able to kill virus-infected and
some cancer cells and require interaction with TH cells to become activated and
proliferate to form clones?
Cytotoxic T cell
What T cell suppresses immune responsiveness to self-antigens (autoimmunity) and switch off the response when antigen is removed?
Regulatory T cell (TREG)
What T cell is developed from activated T cells to provide a ‘rapid reaction force’ for a subsequent encounter with the same antigen and is the basis of persisting immunity?
Memory T cell
Where do plasma cells develop and what do they do?
- mature from B cells in the bone marrow
- synthesize large amounts of antibodies (IgG, IgA, IgD, IgE, IgM)
What are lymph nodes and how are they arranged?
- encapsulated aggregates of lymphocytes & lymphoid tissue, distributed throughout the body
- Arranged in chains or clusters along vessels of lymphatic origin (submandibular, cervical, axillary, femoral, popliteal)
What are the four functions of lymph nodes?
- Non-specific filtering of particulate matter & microbes from lymph
- Interaction of circulating lymphocytes with Ag in lymph
- Aggregation, activation, & proliferation of B-cells with subsequent Ab production
- Aggregation & proliferation of T-cells & induction of cytotoxic immunity
What are immune accessory cells?
antigen presenting cells (macrophages, b and t cells; originate in bone marrow)
What are two types of immune accessory cells/macrophages?
– follicular dendritic cells - macrophages at periphery of germinal centers; Ag-presenting cells
– Tingible body macrophages - 1’ found in germinal centers; possess numerous phagocytic vesicles
What are stromal cells in the lymph nodes?
fibroblasts and reticular cells
What are the three cell types in the lymph nodes?
lymphoid cell
immune accessory cell
stromal cell
What is the morphology of the lymph node?
- Outer, fibrous capsule of dense, irregular connective tissue
- dense, outer, cellular cortex (B and T-cells, & plasma cells) & less cellular inner medulla
- Extensions of cortical tissue into medulla called medullary cords
- Separated by medullary sinuses
- Interspersed throughout cortex & medulla are very thin, collagenous trabeculae
- Blood vessels enter & leave lymph nodes at hilus
What type of follicle are densely packed, highly cellular, and located within the cortex of the lymph node?
primary follicle
What type of follile is paler and contains less dense germinal centers?
secondary follicle
Which type of follicle is responding to anitgens?
secondary follicle
What does proliferation of lymphocytes via clonal expansion and other means do to lymph nodes?
enlargement and “swollen glands”
What is the darker staining rim surrounding a germal center called?
mantleor marginal zone
What is the space beneath the capsule where numerous afferent lymph vessels drain into?
cortical or subcapsular sinus
What is the nature of the endothelium in the lymph node for lymphatic drainage?
endothelium on side adjacent to capsule - continous (prevents leakage)
endothelium on side adjacent to parenchyma - discontinous
Are lymphatic sinuses open spaces like blood sinuses?
NO - filled with reticular fibers and macrophage processes
What is the process where B and T cells leave the bloodstream and enter the node faciliated by complementary adhesion molecules?
diapedesis
Where do B and T cells leave the bloodstream?
specialized post-capillary venules (high endothelial venules)
- lined by cuboidal to columnar endothelium (at the paracortical zone)
What are the sinuses in the outer cortex of the lymph node?
cortical sinuses, trabecular sinuses, or peritrabecular sinuses
What is the path of lymphatic drainage?
- outer cortex sinus
- medullary sinus
- lymph drains from hilus of node via a single efferent lymph vessel
- returns to blood stream via thoracic duct or right lymphatic duct
What is the clinical relevace of lymphatic drainage to regional lymph nodes?
important in metastasis of tumor cells
What are the functions of the thymus?
- Production of mature, immunocompetent Th & Tc cells
- Clonal proliferation of Tc cells
- Clonal deletion of self-Ab’s
- Secretion of hormones regulating t-cell development & maturation
As t-cells mature in the thymus they express?
- Ag specific t-cell receptors
- CD (cluster of differentiation) surface markers
- Class I & II HLA (human leukocyte Ag) surface markers
What does the thymus have that is unique?
hassall’s corpuscles
- eosinophilic lamellated structures within both the medulla and cortex of the thymus
- either degenerated reticular or epithelium nurse cells
What do nurse cells in the thymus secrete?
various hormones (thymotaxin, thymosin, & thymopoietin) to attract, regulate & promote t-cell proliferation & differentiation into Tc, Ts & Th cell
What is the difference between lymph nodes and the thymus?
- thymus is less cellular
- thymus central medulla contains mostly b-cells, plasma cells, and macrophages
- thymus lacks secondary follicles
What is the structure of the thymus?
-highly cellular coretex (t-cells and macrophages)
- secondary follicles absent
- thin capsule of dense, irregular ct
- slender interlobular septa or trabeculae
What is in the outer cortex of the thymus?
– Immature T-Lymphocytes
– Epithelial Cells (Nurse Cells); secrete thymic hormones
– Some Macrophages
What is in the inner medulla of the thymus?
– Epithelia Cells
– Mature T-Lymphocytes
– Thymic Corpuscles (Hassall Corpuscles); Circular aggregations of aged, degenerated Nurse Cells
Which organ degnerates at puberty and is vestigial in adults?
thymus
What process allows for the thymus to degenerate?
- fatty infiltraiton and lymphatic depletion (thymic involution)
- no afferent lymph vessels to thymus because continous epithelium isolates it
- blood-thymus barrier forms an antigenic barrer that isolates thymus from immune system
