Ch 21 Lymphatic System Part 3 Flashcards
Neutrophils
- wander throughout c.t. killing bacteria as it goes
- create a killing zone
- kill more bacteria with toxic chemicals than phagocytosis
Phagocytes
Phagocytic cells with a voracious appetite for foreign matter
Eosinophils
- found especially in mucous membranes
- stand against parasites, allergens and other pathogens
- promote action of basophils
Basophils
- secrete chemicals that aid mobility and action of WBCs and other leukocytes
– secrete leukotrienes, histamine, and heparin - similar to mast cells
Leukotrienes
Activate and attract neutrophils and eosinophils
Histamine
A vasodilator which increases blood flow, speeds delivery of leukocytes to the area
Heparin
Inhibits the formation of clots, which would impede leukocyte mobility
Monocytes
Emigrate from blood into tissues and transform into macrophages
Macrophage system
- all the body’s eagerly phagocytic cells (except for the leukocytes)
- wandering and fixed macrophages
Wandering macrophages
Actively seeking pathogens, widely distributed in loose c.t.
Fixed macrophages
Phagocytize pathogens that come to them
Lymphocytes
- 80% T cells
- 15% B cells
- 5% natural killer cells
Life cycle of T cells
- born in red bone marrow
- mature in thymus
- naïve T cells leave thymus and colonize in lymphatic tissues and organs everywhere in the body
Birth in red bone marrow
From pluripotent stem cells and released undifferentiated into blood and colonize in thymus
Maturation in thymus
Thymosins stimulate maturing T cells to develop surface antigen receptors
Immunocompetent
Capable of recognizing antigens presented to them by APCs
RE cells in thymus
Test T cells by presenting “self” antigens to see if they will recognize the RE cells or attack one’s own tissues
Negative selection
T cells that fail the RE cell test must be eliminated, this leaves the body in a state of self-tolerance in which surviving T cells respond only to foreign antigens
2 forms of negative selection
Clonal deletion and anergy
Clonal deletion
Self-reactive T cells die and macrophages phagocytize them
Anergy
Self-reactive T cells remain alive but unresponsive
B lymphocytes
- started as fetal stem cells in bone marrow
- go through negative selection like T cells if they react to self antigens
- leave bone marrow and colonize same lymphatic tissues and organs as T cells
Self-tolerant B cells
Synthesize antigen surface receptors, divide, produce immunocompetent clones
Antigen-presenting cells
- required to help T cells recognize antigens - alert immune system to foreign antigen
- label every cell of your body as belonging to you
- encounters antigen, internalizes it by endocytosis
6 steps of antigen processing cycle
- Phagocytosis of antigen 2. Lysosome fuses with phagosome 3. Antigen and enzyme mix in phagolysosome 4. Antigen is degraded 5. Antigen residue is voided by exocytosis 6. Processed antigen fragments (epitopes) display on macrophage surface
Interleukins
Chemical messengers that provide signals from one leukocyte to another
Antimicrobial proteins
- Proteins that inhibit microbial reproduction and provide short-term, nonspecific resistance to pathogenic bacteria and viruses
- 2 families: interferons and complement system
Interferons
- Secreted by cells infected by viruses
- alerts neighboring cells
- bind to surface recptors on neighboring cells
- activates NK cells and macrophages to destroy infected cells
Complement system
Group of 30 or more globular proteins that make powerful contributions to both nonspecific resistance and specific immunity
- synthesized by liver, circulate in blood
4 methods of pathogen destruction
Inflammation, immune clearance, phagocytosis, and cytolysis
Inflammation
- C3a stimulates mast cells and basophils to secrete histamine and other inflammatory chemicals
- activates and attracts neutrophils and macrophages
- speed pathogen destruction
Immune clearance
- C3b binds antigen-antibody complexes to RBCs
- RBCs then circulate through liver and spleen
- fixed macrophages there strip off and destroy the Ag-Ab complexes leaving RBCs unharmed
- principle means of clearing foreign antigens from bloodstream
Phagocytosis
Neutrophils and macrophages cannot phagocytize “naked” bacteria, viruses, or other pathogens
- C3b assists them by opsonization
Opsonization
- coats microbial cells
- makes the foreign antigen cell more “appetizing”
Cytolysis
- C3b splits other complement proteins which bind to enemy cell
- attract more complement proteins, and a membrane attack complex forms, this forms a hole in the target cell, electrolytes leak out, water flows in, cell ruptures
3 routes of complement activation
- Classical pathway
- Alternative pathway
- Lectin pathway
Classical pathway
- requires antibody to get started
- antibody binds to antigen on surface of pathogen (forms Ag-Ab complex)
- changes anti body’s shape
Alternative pathway
- nonspecific, does not require antibody
- C3 breaks down in the blood to C3a and C3b. C3b binds directly to pathogen surface, triggers a cascade and autocatalytic reaction, more C3 is formed
Lectin pathway
- plasma proteins bond to carbs
- sets off another cascade of C3 production
What sets off a reaction cascade (complement fixation)?
Exposing a pair of complement-binding sites; binding of 1st complement (C1)
- results in a chain of complement proteins attaching to the antibody
Specific immunity
- composed of a large population of widely distributed cells that recognize foreign substances and act to neutralize or destroy them
2 characteristics that distinguish immunity from nonspecific resistance
Specificity and memory
Specificity
Immunity directed against a particular pathogen
Memory
When re-exposed to the same pathogen, the body reacts so quickly that there is no noticeable illness
Two types of immunity
Cellular (cell-mediated) immunity (T cells) and humoral (antibody-mediated) immunity (B cells)
Cellular immunity
- lymphocytes directly attack and destroy foreign cells
- way of ridding the body of pathogens residing inside human cells
- kills the cells that harbor them
Humoral immunity
- mediated by antibodies that don’t directly destroy pathogens
- antibodies assault the pathogen
- can only work against the extracellular stage of infectious micro organisms
3 stages of cellular and humoral immunity
Recognition
Attack
Memory
Natural active immunity
Production of ones own antibodies or T cells as a result of infection or natural antigen exposure
Artificial active immunity
- prod of ones own antibodies or T cells as a result of vaccination against disease
Natural passive immunity
Temporary immunity that results from antibodies produced by another person
Artificial passive immunity
Temporary immunity that results from the injection of immune serum from another person or animal
Antigen
Any molecule that triggers an immune response
- complex molecules with structures unique to the individual
Epitopes
Certain regions of an antigen molecule that stimulate immune responses
Haptens
Too small to be antigenic by themselves
- must combine with a host macromolecule
- create a unique complex that the body recognizes as foreign
4 classes of T cells of cellular immunity
Cytotoxic T cells, Helper T cells, Regulatory T cells, and Memory T cells
Cytotoxic T cells
Killer T cells (T8, CD8, or CD8+)
- the effectors of cellular immunity
- carry out attack on enemy cells
Helper T cells
(T4, CD4, CD4+) help promote Tc cell and B cell action and nonspecific resistance
Regulatory T cells
(T-regs) - inhibit multiplication and cytokines secretion by other T cells
- limit immune response
Memory T cells
- descend from cytotoxic T cells
- responsible for memory in cellular immunity
2 aspects of T cell recognition
Antigen presentation and T cell activation
Antigen presentation
- APC encounters and processes antigen
- migrates to nearest lymph node
- display it to the T cells
- when T cell encounters the displayed antigen on the MHC protein, they initiate the immune response
MHC-I proteins
- occur on every uncleared cell on body, constantly produced by our cells, transported to, and inserted on plasma membrane
- Tc cells respond only to MHC-I proteins
MHC-II proteins
- occur only on APCs and display only foreign antigens
- TH cells respond only to MHC-II proteins
T cell activation
- Antigen recognition
- Costimulation
- Clonal selection
- Lethal hit, interleukin secretion
Humoral immunity - recognition
- activation begins when antigen binds to several of the B cell surface receptors
- taken into cell by endocytosis
- form APCs on cell surface
- triggers clonal selection of B cells
- some cells differentiate into memory or plasma cells
Humoral immunity - attack
Antibodies bind to antigen, forming the Ag-Ab complex, render it harmless, and tags it for destruction by macrophages
Humoral immunity - memory
Some B cells differentiate into memory cells to allow a much more rapid and numerous response and antibody production to familiar pathogens
Immunoglobulin antibody
Defensive gamma globulin found in the blood plasma, tissue fluids, body secretions, and some leukocyte membranes
Antibody monomer
- 4 polypeptide chains linked by disulfide bonds, w/2 larger heavy chains w/a hinge region where antibody is bent and 2 light chains
- antigen binding site is formed from the variable regions
The variable region
Gives the antibody its uniqueness in all 4 chains
Constant region
Has the same amino acid sequence within one person and determines mechanism of antibody action
5 classes of antibodies
IgA, IgD, IgE, IgG, IgM
IgA
- monomer in plasma; dimmer in mucous, saliva, tears, milk and intestinal secretions
- prevents pathogen adherence to epithelia and penetrating underlying tissues
- provides passive immunity to newborns
IgD
- monomer; B cell transmembrane antigen receptor
- B cell activation by antigens
IgE
Monomer; transmembrane protein on basophils and mast cells
- stimulates release of histamine
- attracts eosinophils to parasitic infections and produces immediate hypersensitivity reactions
IgG
Monomer; constitutes 80% of circulating antibodies in blood plasma
- crosses placenta to fetus, secreted in secondary immune response
IgM
- pentamer in plasma and lymph
- secreted in primary immune response, agglutination
