Basic Components of the Immune System Flashcards
The process by which hematopoietic stem cells (HSCs) differentiate into mature blood cells is called
Hematopoiesis
Primary lymphoid organs
Bone marrow and the Thymus
regulate the development of immune cells from immature precursors
Secondary lymphoid organs:
•Including the spleen, lymph nodes, and specialized sites in the gut and other mucosal tissues
–Coordinate the encounter of antigen with antigen-specific lymphocytes and their development into effector and memory cells.
HSCs are defined by two capacities:
- The ability to regenerate or “self-renew”
- The ability to differentiate into all diverse blood cell types.
One HSC is present per ________ cells in the bone marrow.
5 x 104 (rare)
Myeloid cells and NK cells:
Are memembers of the innate immune system
First cells to respond to infection or other insults
Lymphocytes are:
Members of the adaptive immune response
Generate a refined antigen specific immune response that also gives rise to immune memory
Granulocytes:
Neutrophils, Basophils, Mast cells, and Eosinophils
- All granulocytes have multilobed nuclei
- The cytoplasm contains granules that are released in response to contact with pathogens
Monocytes:
- Migrate into tissues in response to infection
- Can differentiate into specific tissue macrophages:
- Osteoclasts in the bone
- Microglial cells in the central nervous system
- Alveolar macrophages in the lung
Myeloid Antigen-Presenting Cells:
- Monocytes, macrophages, and dendritic cells
- Professional antigen-presenting cell (APC)
- Considered cellular bridges between the innate and adaptive immune systems
Cells of the Lymphoid Lineage Regulate:
Adaptive Immune Response
Lymphocytes:
Three major populations:
– Principal cell players in the adaptive immune response.
– 20% to 40% of circulating white blood cells and 99% of cells in the lymph.
- B lymphocytes (B cells), expresses B cell Receptor
- T lymphocytes (T cells), expresses T cell Receptor
- No contact With antigen: naïve
- Contact antigen: lymphocytes proliferate and differentiate into both effector cells and memory cells.
- Natural Killer Cells (NK cells)
B Lymphocyte (B cell): Derived its letter from its site of maturation
Bursa of Fabricius in birds
Bone marrow in mammals
Mature B cells Display ___________
- Display B-cell receptor (BCR)
- Membrane-bound immunoglobulin (antibody) molecule that binds to antigen.
- Can recognize soluble or particulate antigen
- – Activated B cells differentiate into effector cells known as Plasma cells
- lose expression of BCR and become highly specialized for secretion of antibody
T Lymphocytes:
Derive their letter (T) from their site of maturation in the thymus
Expresses a unique antigen-binding receptor called the
T-cell receptor
–Only recognize processed pieces of antigen (typically peptides) bound to cell membrane proteins called major histocompatibility complex (MHC)
T lymphocytes are divided into two major cell types:
- T cytotoxic (TC), expresses CD8
- T helper (TH) cells, Expresses CD4
- T helper type 1 (TH1) cells regulate the immune response to intracellular pathogens
- T helper type 2 (TH2) cells regulate the response to many extracellular pathogens.
- T helper type 17 cells (TH17), so named because they secrete IL-17, play an important role in cell-mediated immunity and may help the defense against fungi.
NK Cells
Natural Killer Cells
- They are lymphoid cells that are closely related to B and T cells.
- They do not express antigen specific receptors and are considered part of the innate immune system
- They distinguish cells that should be killed from normal cells. How? By “recognizing” the absence of MHC class I, which is expressed by almost all normal cells.
- Express receptors for immunoglobulins, allows them to bind antibodies specific for pathogens .
- This allows NK cell to releases its granules and induces cell death.
Provides niches for hematopoietic stem cells to self-renew and differentiate into myeloid cells and B lymphocytes
Bone Marrow
Most active sites of hematopoiesis
- Long bones (femur, humerus)
- Hip bones (ileum)
- Sternum
Bone marrow contains several cell types that coordinate HSC development:
- Osteoblasts that generate bone and control the differentiation of HSCs
- Endothelial cells that line the blood vessels and also regulate HSC differentiation
- Reticular cells that send processes connecting cells to bone and blood vessels
- Sympathetic neurons , which can control the release of hematopoietic cells from the bone marrow.
Primary lymphoid organ located above the heart where T cells mature
Thymus
Microenvironments of the thymus
- Cortex which is densely populated with immature thymocytes
- Medulla, which is sparsely populated with mature thymocytes.
- These major regions are separated by the corticomedullary junction (CMJ) : Cells enter from and exit to the bloodstream.
_________ are positively selected in the cortex
__________ are negatively selected in the medulla
Thymocytes
Autoreactive thymocytes
Where the immune response is initiated
Secondary Lymphoid Organs
Secondary Lymphoid Organs are distributed throughout the body and share some anatomical features
- Lymph nodes
- Spleen
- Both are the most highly organized of the secondary lymphoid organs and are compartmentalized from the rest of the body by a fibrous capsule
- Mucosa-associated lymphoid tissue (MALT)
- less organized system
- Found associated with the linings of multiple organ systems, including the gastrointestinal (GI) and respiratory tracts
- Tonsils
- Peyer’s patches (in the small intestine)
- Appendix
- Lymphoid follicles within the lamina propria of the intestines and in the mucous membranes lining the upper airways, bronchi, and genitourinary tract.
SLOs share key features:
- All have anatomically distinct regions of T-cell and B-cell activity.
- All develop lymphoid follicles:
- highly organized microenvironments that are responsible for the development and selection of B cells that produce high affinity antibodies.
Lymphoid Organs Are Connected to:
Each other and to infected tissue
–Connected by two different circulatory systems: Blood and Lymphatics
Blood has access to:
virtually every organ and tissue and is lined by endothelial cells that are very responsive to inflammatory signals
The lymphatic system is:
a network of thin walled vessels that play a major role in immune cell trafficking, including:
- The travel of antigen and antigen-presenting cells to SLO’s
- Used for exit of lymphocytes from lymph nodes.
- Lymph vessels are filled with a protein-rich fluid (lymph)
- Lymph is derived from the fluid component of blood (plasma)
- 2.9 liters seeps daily.
Mechanism of lymphatic system
- Foreign antigen gains entrance→ picked up by the lymphatic system→ carried to Lymph nodes that traps the antigen
- Lymph becomes enriched in specific leukocytes, including lymphocytes, dendritic cells, and macrophages.
Where are most secondary lymphoid tissues situated?
•Most secondary lymphoid tissues are situated along the vessels of the lymphatic system.
–The spleen is an exception and is served only by blood vessels.
All immune cells that traffic through tissues, blood, and lymph nodes are guided by small molecules known as _______
chemokines
Proteins are secreted by stromal cells, antigen presenting cells, lymphocytes, and granulocytes, and form gradients that act as attractants and guides for other immune cells
SLO: Lymph nodes
They are:
- Encapsulated
- Bean-shaped structures that include:
- Stromal cells packed with lymphocytes, macrophages, and dendritic cells.
- Connected to both blood vessels and lymphatic vessels
- Lymph nodes are the first organized lymphoid structure to encounter antigens that enter the tissue spaces.
- Provides ideal microenvironments for encounters between antigen and lymphocytes
- Results in productive, organized cellular and humoral immune responses.
Features of the lymph node structure:
- Cortex contains lymphocytes (mostly B cells), macrophages, and follicular dendritic cells arranged in follicles.
- Paracortex which is populated largely by T lymphocytes and also contains dendritic cells that migrated from tissues to the node.
- Medulla is the innermost layer, and the site where lymphocytes exit the lymph node through the outgoing (efferent) lymphatics
- Germinal centers are substructures that facilitate the generation of B cells with increased receptor affinities.
Spleen
- Organizes the Immune Response Against Blood-Borne Pathogens
- Situated high in the left side of the abdominal cavity
- Filtering blood and trapping blood-borne antigens
- Important in the response to systemic infections.
