cells & tissues of the immune system Flashcards
primary lymphoid tissues
where immune cells originate and develop:
- bone marrow
- thymus (site of T cell maturation)
secondary lymphoid tissues
where the immune response is activated:
- lymph nodes
- tonsils
- spleen
- mucosa-associated lymphoid tissue
myeloid WBCs
- neutrophils
- eosinophils
- basophils and mast cells
- antigen-presenting cells (macrophages and dendritic cells)
* RBCs and platelets also come from myeloid precursors
lymphoid WBCs
- B cells
- T cells
- NK cells
Neutrophils
- primary cell of the innate immune system
- ingest and kill pathogens, produce myeloperoxidase, do not present antigen
- maturation: blast -> myelocyte -> band -> neutrophil
- release of granulocyte colony stimulating factor during infection leads to increased myeloid precursors in the peripheral blood as bone marror mobilizes neutrophils

neutrophil

eosinophil
bilobed nuclei, bright pink granules
eosinophils
- innate immunity
- stimulated by IL-5
- increased in parasitic diseases and hypersensitivity
- attach to surface of nematode larvae by binding IgG and IgE produced by B cells (antibody dependent cell mediated cytotoxicity)
- not antigen presenting
- maturation: precursor -> myelocyte -> eosinophil

basophil
(lots of dark granules)

mast cell
basophils and mast cells
- basophils in peripheral blood; mast cells in tissues
- key function = inflammation
- involved in anaphylaxis: receptors for Fc portion of IgE
release histamine and other cytokines
- innate immunity: TLRs on surface recognize PAMPs

monocyte

macrophage
monocytes and macrophages
- monocytes circulate in blood; macrophages are activated in tissues
- innate immunity: phagocytosis of pathogens and debris; cytokine production
- produce IL-1, TNF, IL-12
- adaptive immunity: professional antigen presenting cells
tissue resident macrophages
- alveolar mΦ (lung)
- kuppfer cells (liver)
- microglia (brain)
- red pulp mΦ (spleen)
- tingible body mΦ (germinal center)
antigen presenting cells
- mΦ, dendritic cells, B cells
- link innate and adaptive immunity
- express pattern recognition receptors (TLRs) that bind PAMPs
- MHC class II on cell surface for antigen presentation:
1. engulf pathogens
2. digest proteins
3. express peptides in MHC II
dendritic cells
- antigen presenting cells
- finger like projections help present antigen
- induce T cell and primary antibody response: migrate to lymph nodes to present antigen to CD4+ T cells
- located under skin (langerhans cells) and in mucosa
- lineage: complicated…can be myeloid and lymphoid
B cells
- adaptive immunity: involved in antibody-based humoral immunity
- CD19+ and CD20+
- differentiate into plasma cells that secrete antibodies
- maturation occurs in bone marrow: pro-B cell => pre-B cell => immature B cell

lymphocyte

plasma cell
pale area = golgi….very active protein synthesis for antibody production
plasma cells
- come from B cells
- CD38 and CD138
- produce and secrete antibodies
T cells
- majority of lymphocytes in circulation
- adaptive immunity
- cell mediated immunity: recognize protein antigens (presented by MHC) and kill virus infected cells, tumor cells, foreign cells
- originate in bone marrow and maturation occurs in thymus: CD3+ => CD4+ helper and CD8+ cytotoxic
NK cells
- innate immunity
- directly kills infected cells and tumor cells:
1. recognition of a cell’s lack of MHC class I
2. binding
3. secretion of cytotoxic granules - CD56+ and CD16+
- do not express specific receptors
lymphatic stroma (lymph nodes, nodules, and spleen)
- type III collagen reticular fibers produced by reticular cells
- loose connective tissue
thymus stroma
- branching, interconnected epithelioreticular cells (6 types)
- come from embryonic branchial pouch 3
- stroma, but also involved in T cell education: secrete interleukins, colony stimulating factor, and interferon to promote expression/deletion of CD antigens on T cell surfaces
- types 2 + 5: present self and foreign antigens to T cells at an early stage => must recognize antigens to go from cortex to medulla and continue maturation
- type IV forms thymic (Hassall’s) corpuscles: large, pink staining, concentric curls of keratinized epithelioreticular cells that secrete interleukins

lymph nodules
- dense clumps of B cells in a meshwork of reticular fibers
- found in diffuse tissue of lymphatic organs or in loose connective tissue of GI, respiratory, and urinary tracts
- not considered organs b/c no capsule
- during immune response: geminal center stains lighter due to larger cells with more cytoplasm and euchromatin (due to replication)

lymph nodes
- small organs along lymphatic vessels that “filter” lymph to increase change of antigens encountering mΦ’s and lymphocytes
- structure:
- connective tissue capsule
- outer cortex with nodules (B cells)
- deep cortex with diffuse T cells
- inner medulla with T cells
- trabeculae = connective tissue going from capsule to emdulla

pathway of lymph through lymph node
- afferent lymphatics
- subcapsular sinus (simple squamous epithelium)
- trabecular sinus
- medullary sinus
- efferent lymphatics exiting at hilium
pathway of lymphocytes from blood through the lymph node
entry/exit through high endothelial venules
*simple cuboidal epithelium

spleen function
- platelet resevoir
- destroys defective/aged RBCs (red pulp)
- recycles iron
- immune reactions to blood borne antigens by B and T cells (white pulp)
spleen structure
- dense connective tissue capsule
- red pulp
- splenic sinuses = venous channels with long endothelial cells with gaps bewteen them, parallel to axis of sinus, perpendicular to strips of basal lamina, allow blood cells to pass through walls of sinus
- splenic cords = meshwork of reticular cells and fibers among dense aggregations of RBCs and mΦs
- white pulp
- periarterial lymphatic sheaths = dense aggregates of T lymphocytes + B lymphocyte nodules surrounding central arteries
- spelnic artery enters at hilium => trabecular arteries => central arteries
- connective tissue trabeculae into interior

open system of splenic blood flow
- central arteries => sheathed capillaries surrounded by macrophages => splenic cords where blood percolates through reticular meshwork and macrophages do their thing => splenic sinuses => trabecular veins => splenic vein
*other mammals have a closed system where arterioles => splenic sinuses

thymus function
- T cell maturation
thymus structure
- decays/turns into fat over time after immune system develops
- connective tissue capsule
- interconnected lobules
- cortex has densly packed T cells (stains darker; basophilic)
- medulla has less densly packed cells and geminal centers
- trabeculae carry blood; no sinuses for lymph