Cells and Organs of the Immune System Flashcards
Hematopoiesis
Formation and development of RBS and WBC
White blood cells
Granulocytes
Mast Cells
Monocytes
Lymphocytes
Granulocytes
Look granular under microscope
Include neutrophils, eosinophils and basophils
Myeloid progenitor
Mast cells
Sometimes considered granulocytes
Not present in blood
Precursors migrate from bone marrow into blood to epithelial tissue
Cause allergic reactions
Myeloid progenitor
Differentiate while entering tissues
Blood vessels and nerves
Connective tissue and mucosal mast cells
Resemble basophils
Important initiators of inflammation, contain histamine
Make leukotrienes, prostaglandins, cytokines
Monocytes
Found in blood
Differentiate into macrophages and dendritic cells
Myeloid progenitor
Promonocytes leave one marrow and become monocytes in blood
Circulate for ~8h
Migrate into tissues and become macrophages
Phagocytosis of microorganisms and O-dep and O-indep killing
Lymphocytes
Precursors develop in bone marrow
T cells (70-80%) and NKT cells differentiate in thymus
NK (5-10%) cells differentiate in bone marrow
Lymphoid progenitor
B cells: 10-20%
Thrombopoiesis
Formation of platelets
Myeloid progenitor
Sites of hematopoiesis
Change as we develop
Fetus: yolk sac, liver and spleen, bone marrow
Infants: bone marrow in practically all bones
Adults: vertebrae, ribs, sternum, skull, sacrum, pelvis, femurs
Bone marrow
Primary lymphoid tissue
Involved in production of lymphocytes
Stem cells, microenvironment, hematopoietic growth factors
Hematopoietic stem cell
Express cell adhesion molecules that attach themselves to extracellular matrix and stromal cells
Microenvironment
Created by stromal cells and extracellular matrix
Extracellular matrix
Attachment of stem cells and progenitor cells
Stromal cells
Physical support (scaffold) for growth of hematopoietic cells Provide nutrients, produce hematopoietic growth factors (presented to immobilized stem cells) and express adhesion molecules that influence differentiation Include macrophages, fibroblasts, endothelial cells and adipocytes
Hematopoietic growth factors
Glycoproteins that act at low concentrations
Produced by stromal cells, monocytes and lymphocytes
May affect more than one cell lineage
Show synergistic action with other growth factors
Active on stem cells/functional end cells
Myeloid progenitor growth factors
IL3, CM-CSF, IL6
Lymphoid progenitor growth factors
IL7 +
Granulopoiesis
Neutrophils
IL3, GM-CSF, G-CSF
Granulocytes have segmented nucleus and granules in the cytoplasm
Maintained at steady state in absence of infection
Similar maturation as eosinophils (IL5) and basophil (IL4)
Monocytopoiesis
Same progenitor cells as neutrophils except M-CSF instead of G-CSF
Gradual nuclear folding
Acquisition of cytoplasmic granules
Monoblast to promonocyte to monocyte
Lymphopoiesis
T cells, B cells, NKT and NK cells
IL3, Il7, IL4 +
Stages of maturation defined by surface antigen expression
B Cells
CD20 is marker Mature in bone marrow Activated within primary follicles and then move to secondary follicles to become memory or plasma cells Express membrane-bound immunoglobulin Secrete and produce antibodies
NK cells
Mature within bone marrow
T cells
Mature in thymus
Prothymocytes to thymocytes
Must interact with cytokines and different cell types
NKT cells
Mature in thymus
Prothymocytes to thymocytes
Must interact with cytokines and different cell types
Homeostasis of hematopoiesis
Accomplished by:
- Controlling cytokine production
- Expression of receptors for hematopoietically active cytokines
- Controlled apoptosis
Apoptosis
- Decreased cell volume
- Chromatin condensation
- DNA fragmentation
- Membrane blabbing
Does not cause inflammation
Primary lymphoid tissue
Thymus and bone marrow
Maturation of lymphocytes
Secondary lymphoid tissue
Lymph nodes, spleen, various mucous associated lymphoid tissues (MALT) (i.e.. GALT)
Antigen is trapped, providing opportunity for interaction with mature lymphocytes and antigen-dependent maturation of T and B cells
Tertiary lymphoid tissues
Contain few lymphoid tissues than secondary lymphoid organs
Import lymphoid cells during inflammatory response
ie. Cutaneous-associated lymphoid tissue (CALT): first site where a pathogen puncturing epithelial cells encounters immune cells
Thymus
Sure of T and NKT cells maturation
Large in babies, shrinks in pregnancy
Bi-lobed, encapsulated organ with lobules separated by connective trabecular
Outermost cortex is densely packed with immature, proliferating thymocytes (undergoing apoptosis)
Inner medulla is sparsely populated with mature thymocytes undergoing positive and negative selection
Lymphatic system
Network of vessels that collect fluid from tissues
Mature lymphocytes circulate in lymphatic system
Lymph is collected and eventually drain into thoracic duct
Afferent lymphatic vessels
Bring lymph fluid containing antigen carrying dendritic cells, particulate antigen and lymphocytes to regional lymph nodes
Efferent lymphatic vessels
Take lymph fluid from lymph nodes into venous circulation
Carry antibodies secreted by plasma cells, activated/memory T cells and B cells
Lymph nodes
Bean shaped capsule, distributed around vessels
Sinuses
Cortex (outside), paracortex, medulla (inside)
Site of generation of T and B cell antibody responses to specific antigen
Site where lymphocytes can interact with antigens and presenting cells (esp interdigitating dendritic cells)
Phagocytosis of particulate matter prevents entry into blood stream
Lymph node cortex
Outside-most
Primary follicles and secondary follicles
Primary follicles of lymph nodes
Naive B cells, follicular dendritic cells, macrophages
Follicular dendritic cells
Concentrated antigens to make them more readily available to B cells
Secondary follicles
Activated B cells in germinal layers: proliferating and undergoing expansion and differentiation
Paracortex of lymph node
T cells, interdigitating dendritic cells
Site where T cells respond to foreign antigens presented by dendritic cells
Medulla of lymph node
Phagocytic macrophages, antibody secreted plasma cells, some activated/memory T and B cells moving into the efferent lymph
High endothelial venules
Sites within vasculature of lymph nodes that are specialized to allow B and T cells to move from blood into lymph nodes
T and B cells that have not become activated by antigens exit via efferent vessel to go to another node
Spleen
Immune responses are mounted against antigens in the blood
Old/defective RBCs are phagocytosed and recycled
Large, ovoid organ in upper left quadrant of abdominal cavity
White and red pulp separated by marginal zone
Swells during infection
White pulp
In spleen
Generation of T cell responses and B cells responses against blood borne antigens
Marginal zone
Interdigitating dendritic cells trap blood borne antigens and transport them to white pulp
Surrounds vascular bed
Red pulp
Defective/old RBCs and blood born pathogens are phagocytosed by macrophages
Neutrophils
AKA polymorphonuclear leukocyte (multi lobed appearance)
Produced in bone marrow and released into blood
Circulate for 7-10h
Migrate into tissue and die within 48h, signal from macrophages and tissue
Segmented nucleus connected by chromatin strands
Primary and secondary granules
Primary phagocytosis of bacteria and debris
Killing of ingested bacteria (O dependent and O independent)
O dependent neutrophil killing
Reactive O intermediates
Reative nitrogen intermediates
O independent neutrophil killing
Defensives
Lysozyme
Hydrolytic enzymes
Tumor necrosis factor
Eosinophils
Produced in bone marrow and released into blood
Segmented nucleus, spherical granules
12-17nm
Anti parasitic function
Involved in allergic reactions
Contain lysosomal and oxygen radicals
Contain eosinophil cationic protein: anti-parasite protein
Basophils
Produced in bone marrow and released into blood
Segmented nucleus, spherical purple granules
Back up mast cell responses in inflammation, involve din allergic reactions, contain histamine
Make leukotrienes and prostaglandins
Macrophages
Travel by amoeboid movement
Named based on location
Recruitment of immune system cells into inflammatory site
Secrete cytokines and chemokine
Present antigen to T cells: Class 1 and 2 MHC
Activated by phagocytosis, Th1 cytokines (IFNgamma), inflammatory mediators, bacterial components
Dendritic cells
Produced in bone major
Released into blood
Migrate into various tissues
Most potent professional antigen presenting cells: do not have to be activated
Long membrane extensions
MHC1 and MHC2
Migrate to lymph nodes and present antigen to T cells
NKT cells
Express functional T cell receptors that interact with CD1 instead of Class 1 and 2 MHC
Innate immunity
CD4+ T cells
Help activate CD8+ T cells, B cells, macrophages and other immune systems
Regulate immune responses
Function by producing a range of different cytokines
CD8+ T cells
Kill virus-infected cells and cancer cells
