Immune System Flashcards
immune System consists of:
- cells: lymphocytes, antigen-presenting cells
- lymphatic tissue: diffuse and nodular
- lymphatic Organs: lmyph nodes, Spleen, Thymus
- lymphatic vessels
Main functions of immune system
- production of immune cells
- Monitoring Body tissues
- reaction to harmful Antigens
- storage of blood and lymph
Antigen (Ag)
- target for specific immune Response
- soluble substance or infectious organism
Cellular (cell-mediated) immunity
- mediated by T lmyphocytes
- attack and destroy virus-infected host cells
- no antibodies released
Humoral (antibody-mediated) immunity
- antibodies act directly on invading Agent
- antibodies produced by Plasma cells derived from B lymphocytes
Functional classification of lmyphocytes
- B cells
- T cells
- NK cells
Morphological classification of lymphocytes
small
medium
large
in circulating blood: majority are small
in tissues and Organs: medium and large
T cells
- differentiate in Thymus
- 60-80% of circulating lymphocytes
subtypes: Helper T Cytotoxic T Regulatory T Gamma/Delta T
Helper T cells
- secrete cytokines
- interact with cytotoxic T, NK and macrophages in cellular Response
- interact with B cells for initiating humoral response
Cytotoxic T cells
- kill target cells
- release:
>perforins: create channels in cells Plasma membrane
>granzymes: into target cells, activate apoptosis
Regulatory T cells
- can supress an immune Response to Antigen
Gamma /Delta T cells
- develop in Thymus
- migrate to epithelial tissues (intraepithelial lymphocytes)
- first line of defense against invadors
- kill cells similar to CT cells
- do not recirculate!
B cells
20-30%
- differentiate into Plasma cells
Plasma cells
- large eccentric nucleus
- synthesize and secrete anitbodies –> immunoglobins
- immunoglobins M, A, D, E, G
- antibody binds to Antigen: antibody-Antigen complex
- eliminated by phagocytosis
Natural Killer (NK) cells
5-10%
- recognize transformed cells (Virus or Tumor)
- similar mechanism as CT cells
Antigen-presenting cells
- lymphocytes can only recognize Antigens broken down and presented by APCs
- Antigen –> 8 to 10 aa Peptides on APC cell Surface
- most APCs belong to MPS
Mononuclear phagocytotic system
- derived from monocytes
macrophages in CT, lungs, Spleen
Kupffer cell, microglia, M cells
Langerhans cells, Dendritic cells
Primary lymphatic organs
Bursa-equivalent Organs (for B cells)
- bone marrow
- gut-associated lymphatic tissue (GALT)
Thymus (for T cells)
Secondary lymphatic organs
lymphatic nodules
lymph node
spleen
Primary lymphatic Organs - what they do
- initial education Centers
- cells differentiate into immunicompetent cells
- –> can differentaite “self” vs “non-self”
- differentation is antigen-Independent
- lymphocytes then enter blood to populate secondary organs
Secondary lymphatic Organs - what they do
- secondary education Centers
- immunocompetend lymphocytes differentiate into:
>immune effector cells
>Memory cells - These cells undergo antigen-dependent activation
Primary immune respinse
- body’s first Encounter with an Antigen
- characterized by lag period of several days before Antigen is detected
Secondary immune response
- more rapid and intense
- presence of Memory lymphocytes that are programmed to respond
Bone marrow
YELLOW BONE MARROW:
- in adults
- consists of fat cells
- occupies diaphysis of Long bones
RED BONE MARROW:
- in adults: in flat bones and epiphyses of Long bones
- in new Born: all bone marrow is red
in extreme blood loss: yellow marrow can revert to red marrow
Red bone marrow
stroma: reticular cells and fibers with fat cells, fibrophages, macrophages…
parenchyma:
- blood cells in different stages arranged as Cords
- erythrocytes nest: near sinusoids
- granulocytes and lymphocytes: nest farther away from sinusoids
- Megakaryocytes: adjacent to sinusoidal wall
Gut-associated lymphatic tissue
lymphatic nodules of the distal gut
- submucosa of Ileum (Peyer’s Patches)
- submucosa of appendix
Thymus main functions
T-cell initial education
Population of secondary lymphatic organs
Organization of Young thymus
dense irregular CT capsule
trabeculae divide into irregularly shaped lobes
Stroma: Epithelioreticular cells (ERCs)
Parenchyma: T cells /thymocytes
Lobe of thymus
Cortex: a lot of lmyphocytes
Medulla: fewer lympocytes
Developmental Sources of thymus
Stroma: endoderm (Invagination of Epithelium f 3rd pahyngeal pouch)
Capsule and trabeculae: mesenchyme
Epithelioreticular cells (ERC)
Functions:
- Framework for developing T cells
- blood-thymus barrier
- substances for education of cells
- form thymic corpuscle
Bloor-Thymus barrier
Endothelium of capillary wall
Perivascular connective tissue
Epithelioreticular cell layer
T cell “initial education”
Enter MEDULLA via postcapillary venules
into CORTEX for positive selection
—> Cells that recognize self/non-self pass
into MEDULLA for negative selection
—> Cells that recognize SELF antigents are eliminated
Thymic (Hassall’s) corpuscle
- In Medulla of older Thymus
- produce Interleukins –> influence Differentiation of T cells
- concentrically arranged ERCs
- in Center: keratinization or calcification
Thymic involution
- at puberty
- T cells leave the Thymus to populate secondary lymphatic Organs
- Thymus Skinks and fills with Hassall’s corpuscle and fat cells
MALT
mucosa-associated lymphatic Organs
accumulations of lymphatic tissue without capsule
GALT is part of MALT
consists of intraepithelial lypmocytes (Gamma /Delta T)
Diffuse lymphatic tissue
diffuse Aggregation of lymphocytes in LAMINA PROPRIA of:
- GI
- Respiratory
- Urogenital
Lymphatic nodules
- oval Aggregation of lymphocytes in
LAMINA PROPRIA or SUBMUCOSA
composed of T and B cells, antogen presenting cells
Primary vs secondary nodules
Primary nodules
- lmyphocytes are not activated
- no germinal centers
Secondary nodules
- germinal Centers
- when B cells are presented with Antigen, reveice T cell help
- B-cells –> lmyphoblasts –> Plasma cells and Memory cells (this happens in germinal Centers)
Tonsils (MALT of Pharynx)
form waldeyer’s tonsillar ring
pharyngeal tonsils
Tubal tonsils (around Openings of Eustachian tubes)
—> These two have Respiratory Epithelium
Palatine tonsils
Lingual tonsils
—> These two have stratified squamous epithelium
Structure of the tonsils
- Epithelium Dips into Underlying CT to form crypts
- wall of crypts contains intraepithelial lmyphocytes, diffuse lymphatic tissue and lymphatic nodules
Lymph nodes
- conctentrated in Axilla, groin, mesenteries
- encapsulated
- Filtration and contact with Antigen
- Environment for secondary education
Lymph node structure
capusle: dense CT
Stroma: reticular CT
Parenchyma: immune cells
Cortex (B cells in Primary and secondary nodules)
Paracortex (T cells)
Medulla (B cells and medullary Cords and sinuses)
look at Picture!!!!!!
Lmyphatic circulation of lymph node
- afferent lmyphatic vessels
- subcapsular Sinus
- trabecular Sinus
- medullary Sinus
- efferent lymphatic vessels
in sinuses: lmyph with macrophages and reticular cells
Blood circulation in lmyph node
artery in Hilum arterioles in paracortex capillary beds in Cortex high endothelial postcapillary venules in paracortex hilar vein
High endothelial postcapillary venules
- cuboidal endothelial cells
- important in circulating and concentrating lymph
- site of Exit of lymphocytes (90%)
Spleen organization
- capsule (dense CT and myocytes)
stroma: reticular CT
Parenchyma: blood cells
White Pulp vs red Pulp
look at Picture!!!!!!
Main functions of spleen
immune functions:
- filters and Monitors blood
- Environment for secondary education
Hematopoietic function:
- Formation of blood cells in fetal life
- removal of RBCs and platelets
- Retrieval of ion
Storage of blood
Splenic circulation
open circulation in humans:
- Splenic artery
- Trabevular arteries
- Penicillar arterioles
- Red Pulp
- Spleic Cords
- Splenic sinuses
- Pulp venules
- Trabecular vein
- Splenic vein
closed circulation in animals … Penicillar arterioles capillaries splenic sinuses ...
White Pulp of spleen
lmyphatic Aggregation around central arteries
- periarterial lmyphoid sheaths (PALS, mostly T cells)
- lmyph nodules (mostly B cells)
Splenic follicle
Periarterial Zone: around central artery, T cells
Germinal Center (B cells)
Mantle Zone (around germinal Center) T and B cells
Marginal Zone (around follicle) T and B cells
Red Pulp of spleen
splenic Cords
splenic sinuses
Splenic cords
Contain blood cells: RBCs , neutrophils, pletelets, macrophages
Reticular Framework supports the Cords
Cords are between sinusoids
Splenic sinuses
Endothelial cells
Discontinuous b.n.
Reticular fibers around sinuses
