Lecture 18: Immune lymphatic systems Flashcards
Innate immunity
Lacks immune specificity and memory
Respons=inflammation
Neutrophils are first responders
Aquired immunity
Develops in response to antigens
More powerful than innate
Takes longer to develop
Displays specificity and memory
Passive immunity
Temporary immunity due to donated antibodies (i.e., transplacental passing of maternal antibodies to fetus)
Active immunity
Long lasting/permanent immunity due to self exposure to antigen resulting in memory T cells and B cells specific for antigen
Primary lymphoid organs
Thymus and bone marrow
Secondary lymphoid organs
Lymph nodes, spleen, tonsils
Primary lymph follicle
Spherical, tightly packed accumulations of virgin B cells and dendritic reticular cells that have not been exposed to antigens
Secondary lymph follicle
Are derived from primary follicles that have been exposed to nonself antigens
Are not present at birth
Contain cortex and germinal center
All immune system cells originate in
Bone marrow
IgA
Found in saliva, milk, GU and respiratory tracts
IgD
Found on surface of B cells traveling to lymphoid organs
IgG
Major Ig in blood
Responsible for most antibody activity
IgE
Associated with allergic responses
IgM
First antibody class expressed by developing B cells
Major histocompatibility complex (MHC) gene products function
Main function of MHC gene products is the presentation of antigenic peptides to T cells
MHC I
Expressed on the surface of all cells except trophoblast and RBC
MHC II
Expressed on the surface of B cells and antigen-presenting cells
CD8+ T cells
Bind to antigen presenting cell- MHC I molecules
Release perforins and fas ligand
CD4+ cells
Recognize antigens bound to MHC II molecules
Helper cells- Assist CD8+ T cell differentiation
Assist B cell differentiation
CD16+ T cells
Natural killer T cell
Activated by tumor cell antigens and release cytokines
Complement system definition
Array of about 20 serum proteins which are synthesized in the liver and found in the blood
Classic pathway activation
Antibody binding to a pathogen
Alternate pathway activation
Directly activated by pathogen
First steps in compliment cascade
Immunoglobulins bind to surface of pathogen
C1q binds to Fc region of Ig
Activates C1r
Activates C1s
Most important opsonin
C3b
C1s sequences
C1s–>C4–>C4a + C4b
C1s–>C2–>C2a + C2b
C2b binds C4b–> C4b-C2b complex
C6, C7, C8, C9 added to complex to form
Pores in the membrane of the pathogen
Complement cascade leads to
Activation of membrane attack complex (MAC) on the pathogen leading to perforation and lysis
Production of opsonins, which are coatings that make the antigen more palatable to phagocytes
Release of chemotactic agents which attract phagocytes to the areas of infection/inflammation
Parenchyma consists of
Cells that typically pack areas of the lymphoid organ
-mostly lymphocytes
Stroma consists of
Mostly of reticular fibers and cells, including undifferentiated cells and fixed and free macrophages
Lymph node hilus
Entry and exit point for vessels
Lymph node capsule
Dense collagen fibers, some elastic fibers and smooth muscle fibers
Lymph node outer cortex
Contains lymph follicles
Lymph follicles contain
B cells
Follicular dendritic cells
Migrating dendritic cells
Secondary lymph follicles contain
Mantle, germinal center
–Primary lymph follicles lack these
Lymph node inner cortex
Contains Helper T cells, macrophages
High endothelial venules (HEVs)
HEVs are
Port of entry for circulating differentiated lymphocytes to seed node
Lymph node medulla
Irregular arrangement of loose medullary sinuses and dense medullary cords
Site of lymphocyte reentry into lymph stream
Thymic-dependent areas in subcortical and deeper medullary regions
Medullary sinuses are lined with
Macrophages
Medullary cords consist of
Blood vessels, lymphoblasts and plasma cells
Thymus capsule contains
Blood vessels
Efferent lymphatics
NO afferent lymphatics, therefore, lymph does not circulate through thymus
Extends trabeculae into parenchyma
Trabeculae of thymus
Delicate CT
Divide thymus into incomplete lobules
Thymus lobule cortex
Stains darkly
Containes epithelial reticular cells and T cells
Thymocytes migrate from cortical areas to medullary areas
Blood vessels surrounded by continuous epithelial barrier
Thymus lobule medulla
Light staining
Specialized to allow entry channel into blood stream of mature lymphocytes
Capillary beds NOT sheathed by epithelial cells
Contain Hassals corpuscles
Hassals corpuscles
Whorls of highly keratinized medullary epithelial cells
Produce cytokine thymic stromal lymphopoietin
–Stimulates thymic dendritic cells needed for the maturation of single positive T cells
Double negative T cells
Lack cell surface molecules typical of mature T cells
Enter cortex from blood vessels
Proliferate in subcapsular area
Double negative T cells migrate
To outer cortex
Confronted by cells with cell surface MHC I and II
Express both CD4 and CD8 receptors and TCR receptors
Single positive T cells migrate
To inner cortex
Express TCR receptors and either CD4 or CD8 co-receptors
Blood thymic barrier
Located in thymic cortex
Prevents antigens in the blood from reaching developing T cells in thymic cortex
Leaky during fetal life to develop tolerance
Spleen characteristics
No lymph sinuses No afferent lymph vessels Covered by peritoneum except at hilus Blood vessels enter and leave at hilus Divided into red/white pulp
Spleen blood filtering functions
Only lymphatic organ specialized to filter blood Stores and removes worn-out RBCs Recycles iron Converts hemoglobin to bilirubin Blood formation in the fetus
Spleen immunologic functions
Screen foreign material in blood
Produces lymphocytes and plasma cells
Removal leads to overwhelming bacterial infections in infants, children and young adults
White pulp
Always associated with arteries
Zones of diffuse lymphoid tissue and germinal centers
Site of clonal expansion of antigen stimulated lymphocyte
B cell area contains secondary follicles in which central arteriole is off center
T cells found where in white pulp
In the areas surrounding the central artery near the center of white pulp
Forms periarterial lymphatic sheath
Marginal zone
Forms sinusoidal interface between red/white pulp
Has abundance of antigen-presenting cells
Lymphocytes first encounter antigens here
Activated Helper T-cells activate B-cells here
Red pulp
Surrounds white pulp and makes up 80% of spleen
Functions to filter blood
Contains large number of RBCs
Billroth cords
Form red pulp parenchyma
Contain various cells
Terminal capillaries open directly into substance of cords
Macrophages destroy worn-out or defective RBCs
Venous sinusoids
Endothelial-lined sinusoids with a discontinuous basement membrane
Storage sites for healthy RBCs
Sequence of flow of red blood cells through spleen
Splenic artery Trabecular arteries Central arteries Penicillus Venous sinuses
