Lymphoid and Immune Systems Flashcards
lymphatic system functions
- reclaim lost fluid for return to cardiovascular system
- protect against pathogens & cancer cells- non-specific and specific
immunity
resistance to infection through activation of specific defenses
non-specific defenses
general protection
does not distinguish threat specifics
specific defenses
immune response
identify and defend against one particular threat
lymphatic system components
- lymph- fluid similar to plasma but less proteins
- lymphatic vessels- carry lymph from tissues to veins
- lymphoid tissues and organs- site of development of lymphocytes and screening for pathogens
- lymphocytes and phagocytes- provide defense
lymphocytes are produced
in lymphoid tissues (ex. tonsils)
lymphoid organs (ex. spleen, thymus)
and in red bone marrow
the circulation of fluids
from blood plasma to lymph and back to the venous system
also transports hormones, nutrients and waste products
lymph and lymphatic vessels
lymph originates as fluid lost from blood capillaries
fluid collected in blind end lymphatic capillaries
endothelial cells loosely bound together with overlap acts as one-way valve: allows fluids, solutes, viruses and bacteria to enter and prevents return to intercellular space
fluid, solutes, large objects drive into lymphatic capillary by pressure in interstitial space
lymphatic vessels
histologically most like veins
three tunics
large ones have vasa vasorum
many valves
many anastomoses
lymph nodes present along vessels
lymphatic vessels
converge, return fluid to blood stream: lymphatic capillaries-> lymphatic collecting vessels-> lymphatic trunks-> subclavian veins
lymphoid cells
- macrophages- phagocytosis and T cell activation
- dendritic cells- antigen presentation (found in CT)
- lymphocytes- constantly circulate between blood, lymph, tissues, can survive 20+ years, 3 classes: T cells, B cells, and Natural Killer cells
T cells
“thymus dependent”, 80% of circulating lymphocytes
main types of T cells
cytotoxic (TC) cells- cell mediated immunity, kill “foreign” cells and viruses directly
memory T cells- formed in response to foreign substance, remain in body to give “immunity”
helper T (TH) cells- activate T & B cells
suppressor T (TS) cells- inhibit T & B cells
B cells
“bone marrow derived”, 10-15% of circulating lymphocytes
antibody mediated or humoral immunity
when activated-> plasma cells-> secretes antibodies (immunoglobin proteins)-> antibodies bind specific antigens (any pathogen or foreign compound)
Natural Killer cell
5-10% of circulating lymphocytes
nonspecific defense
responsible for immunological surveillance
attack abnormal cells- cancer cells, foreign cells or virus-infected cells
lymphopoiesis
occurs in bone marrow, thymus and lymphoid tissues
hemocytoblast-> lymphoid stem cell
one type of lymphoid stem cell stays in bone marrow-> produce B cell and NK cells
one type migrates to thymus-> produce T cells
both B and T cells
can divide to produce more of the same type (clones)
can migrate to all lymphoid tissues for division and development
lymphoid tissue
reticular CT, lymphocytes, and other lymphoid cells
function of lymphoid tissue
- proliferation site for lymphocytes
- surveillance point for lymphocytes and macrophages
two types of lymphoid tissue
- lymphoid follicles/nodules
- lymphoid organs
lymphoid follicles/nodules
CT packed with lymphocytes- T, B and dendritic cells
no capsule
germinal center middle with dividing B cells- surrounded by dendritic cells, T cells and some macrophages
follicles associated with respiratory, digestive, and urinary tracts
special lymphoid nodules: MALT, appendix, tonsils
MALT (mucosa-associated lymphoid tissue)
deep to intestinal epithelium
made up of individual nodules called Peyer’s Patches
appendix
tubular offshoot of beginning portion of large intestines
tonsils
large nodules in pharynx, have crypts to trap bacteria-> encourage development of immunity
5 total: 2 palatine tonsils, 1 pharyngeal (adenoid), 2 lingual tonsils
lymphoid organs
have fibrous CT capsule around outside
contain many lymphoid follicles
include: lymph nodes, thymus, spleen
lymph nodes
bean shaped, 1-25 mm
have associated blood vessels and nerves
lymph node structure
capsule= CT, surrounds outside
trabecular= folds of capsule crating partitions inside
cortex= outer edge
superficial cortex= lymphoid follicles with B cells and dendritic cells
deep cortex= T cells, transit between lymph and blood
medulla= center, houses T, B and plasma cells
sinuses= spaces throughout that house macrophages- allow lymph flow through node
lymph flow through node
- lymph enters via many afferent vessels- from peripheral tissues to lymph node
- flows slowly through sinuses where it is surveyed for pathogens and antigens- macrophages engulf pathogens, dendritic cells bind antigens and stimulate lymphocytes
- “clean” lymph exits via few efferent vessels that carry lymph to venous circulation
lymph nodes clustered
mostly along lymphatic trunks, nodes function to purify lymph before returning it to blood
if pathogen detected in node
- pathogen detected- antigens are “presented” to lymphocytes to stimulate lymphocytes
- lymphocytes increase in number- rapid clonal division of B & T cells
- causes node to swell= buboes
lymph node diseases
lymphadenopathy= chronic enlargement of lymph nodes, due to infection or cancer
cancer often metastasizes in lymph vessels- blood capillaries restrict access of cells but lymphatic capillaries do not
thymus
T cells mature in cortex and migrate to medulla to enter blood
thymus produces hormones- thymosin & thymopoietin- both promote development and maturation of lymphocytes, mostly the T cells in thymus
thymus most active in early childhood
thymus atrophies with age
spleen
located lateral to stomach
functions to remove abnormal blood cells, store iron from recycle RBCs for reuse, initiate immune response by B & T cells in response to antigens in blood, store platelets, site of fetal erythrocyte production
structure of spleen
red pulp- sinusoids filled with RBCs, platelets and macrophages which phagocytose old RBCs and pathogens
white pulp- lymphoid follicles containing lymphocytes, await antigen to activate
spleen cleans blood
blood flows slowly through sinusoids
macrophages and lymphocytes detect and destroy foreign cells and antigens
sinusoids
bleeds profusely when damaged
to fragile to stitch tears
splenectomy to prevent fatal hemorrhaging
liver and bone marrow can take over functions
body defenses against pathogens
provide resistance to fight infection, illness, and disease
2 categories of defenses: nonspecific and specific defenses
three lines of defense
1st line: prevent entry-> skin & mucosa
2nd line: general antimicrobial actions when first line has been penetrated- nonspecific defense= innate defense
3rd line: precision assault on a specific pathogen- specific defense= immune response
nonspecific defenses
always work the same way
against any type of invading agent
born with it
7 types of nonspecific resistance
- physical barriers
- phagocytic cells
- immunological surveillance
- interferons
- complement
- inflammation
- fever
physical barriers
- cutaneous membrane (skin)
- mucosa
cutaneous membrane (skin)
impenetrable layers of keratinized cells
impermeable to water and chemicals
acid pH due to sebum
high salt due to perspiration
acid and salt inhibit microbial growth
mucosa
produces antimicrobial secretions:
acid-> inhibit microbe growth
lysozyme-> lyse bacterial cell walls
mucus-> traps microbes
phagocytes
- microphages
- macrophages
microphages
neutrophils and eosinophils
either phagocytose pathogens OR secrete defensins on pathogen
defensins cause membrane pores that result in lysis of target cell
macrophages
phagocytose pathogens, cell debris and foreign material
fixed macrophages-> non-traveling, associated with specific tissues or organs (ex. microglia)
free macrophages-> travel throughout body via blood
all phagocytes
emigrate from capillaries
display chemotaxis
have receptors to bind target for phagocytosis
phagocytosis process
- phagocytic cell adheres to target via receptors
- pseudopods from around target to engulf
- target internalized in phagosome-> fused with lysosome
- target digested in phagolysosome: small solutes diffuse into cytoplasm for use- amino acids, glucose, etc. undigestable= residual body
- enzymes neutralized and residual body is exocytosed
immunological surveillance
means monitoring of tissues by NK cells for abnormal cells (cancer or virus infected)
1. abnormal cells express abnormal antigens on the surface-> detected by NK cells
2. NK cell binds abnormal cell and releases perforins from Golgi
3. perforins assemble on target membrane creating pores-> lysis of target
interferons
- antiviral cytokines= chemicals used for cell to cell communication
- proteins released by activated lymphocytes, macrophages, or virus-infected cells
three types of interferons
alpha, beta, gamma
alpha interferons
produced by leukocytes
stimulate NK cells
beta interferons
secreted by fibrocytes
slow inflammation
gamma interferons
secreted by T cells and NK cells
stimulate macrophage activity
complement
11 complement proteins + 9 other factors & regulators act in cascade to cause foreign cell lysis (often target bacteria)
1. classical pathway
2. alternate pathway
binding of C3b= “complement fixation”-> triggers anti-microbial effects
inflammation
localized redness, swelling, heat, and pain in response to any tissue damage
function to help prevent injury/infection from spreading, disposes of cell debris, sets the stage for repair
fever
elevated body temperature >99F/37.2
triggered by pyrogens, material that causes the hypothalamus to raise body temperature: released into blood by leukocytes (mostly macrophages) when exposed to foreign antigens
effect-> increase metabolic rate to allow better defense and repair-> rate increases 10%/1C
fever temperatures
temperature up to 104F: safe and productive
at 106F-> nervous tissue dysfunctional
at 110F-> proteins denature=death
nonspecific and specific defenses
operate together to provide resistance to infection and disease
specific defenses
protect against specific pathogens
depend on activities of lymphocytes
specific resistance (immunity): develops after exposure to environmental hazards
4 properties of immunity
- specificity
- versatility
- memory
- tolerance
specificity
each B or T cell responds only to a specific antigen and ignores all others
versatility
the body produces many types of lymphocytes
each fights a different type of antigen
active lymphocytes clones itself to fight specific antigen
memory
some active lymphocytes (memory cells):
stay in circulation
provide immunity against new exposure
tolerance
immune system ignores “normal” antigens (self-antigens)
T cells
cellular immunity (cell-mediated immunity)
function to amplify the inflammatory response
B cells
humoral immunity (antibody-mediated immunity)
responsible for most complement activation/fixation
B and T cells
covered in receptor that recognize and bind only one specific antigen
antigen
foreign substance that can activate the immune system and provoke an immune response
usually large complex molecules-> proteins, nucleic acids, some lipids, some polysaccharides
pathogens
a bacterium, virus, or other microorganism that can cause disease
simple chemical structures
like plastic and metal are not immunogenic/antigenic
T cells and cell mediated immunity
targets virus or parasite infected cells, cancer cells, and cells of foreign grafts
T cells must be activated by exposure to antigen
do not recognize free antigen
antigen must be bound to special glycoprotein receptors on target cell: major histocompatibility complex (MHC)
main types of T cells
- cytotoxic T cells
- helper T cells
- memory T cells
- suppressor T cells
cytotoxic T cells
carry out cell mediated immunity
physically attack foreign cells
helper T cells
activated B and Tc cells
memory T cells
clone more of themselves in response to “remembered” antigen
suppressor T cells
moderate the immune response by inhibiting Tc and B cells
MHC proteins
the membrane glycoproteins that bind to antigens
genetically coded in chromosome 6: the major histocompatibility complex (MHC) differs among individuals
two classes of MHC proteins
class 1: found in membranes of all nucleated cells
class 2: found in membranes of antigen-presenting cells (APCs) found in lymphocytes
class 1 MHC proteins
pick up small peptides in cell and carry them to the surface: T cells ignore normal peptides, abnormal peptides or viral proteins activate T cells to destroy cell
class 2 MHC protein
found on lymphocytes and antigen presenting cells (APC)
bind exogenous antigens (material that have been phagocytosed and broken down)
activated Th cells which activate B cells and Tc cells
APC
dendritic cells, Langerhans cells, macrophages, activated B cells
APC are responsible for activating T cells against foreign cells and proteins
class 1 and class 2 MHC recognition
each T cell detects only one antigen and only when it is in either class 1 MHC or class 2 MHC
Tc and Ts: respond to antigen in class 1 MHC
Th: respond to antigen in class 2 MHC
organ transplants
graft rejection:
tissue typing: attempt to match MHC, but antigens in MHC will always be foreign, thus attacked
need immuno-suppressive drugs to suppress Tc cell activity to save graft
activation of helper T cells
- bind antigen in class 2 MHC
- proliferation/clonal selection
- memory cells
- active helper T cells
costimulation
by cytokines from active phagocytes
Tc cells may destroy target cells through release of
cytokines, lymphotoxins, or perforin
T cell activation usually involves:
antigen presentation by phagocytic cell
cell-mediated immunity
involves close physical contact between activated Tc cells and foreign, abnormal or infected cells
B cells and antibody mediated immunity
targets bacteria, bacterial toxins, and free viruses
B cells
responsible for antibody-mediated immunity
attack antigens by producing specific antibodies
millions of populations, each with different antibody molecules
activation of B cells: T dependent antigens
- B cells have antibodies (IgD) on surface as receptor for antigen-> binding causes B cell to become sensitized
- bound antigen is internalized, processed, and reappear back on the surface bound to class 2 MHC protein
- a specific Th cell recognizes the antigen + MHC complex and releases cytokines to activate the B cell
- activated B cell proliferates (clonal selection) to produce memory B cells and plasma cells
initial exposure to antigen
~5 days B cell-> plasma cell
~10 days to peak antibody levels (titer) in blood
antibodies (IgM) circulate ~2 weeks
second exposure to antigen
memory cell-> plasma cell ~1-2 days
peak titer ~2-3 days, higher level
antibodies (IgG) circulate weeks-months
primary and secondary responses
occur in both cell-mediated and antibody-mediated immunity
antibody (Ab) structure
2 parallel pairs of polypeptide chains: 1 pair of identical heavy chains and 1 pair of identical light chains- held together by disulfide bonds
hinge region= flexibility
each chain contains: constant segments and variable segments
constant segments (C) of antibody
determine class of antibody molecules
have sites for complement binding (Fc region)
variable segments (V) of antibody
determine antigen specificity of antibody
make up antigen bind sites
humans produce 100 million- 1 billion different anitbodies that
each bind a different antigen
5 heavy chain constant segments determine 5 types of antibodies
IgG
IgM
IgA
IgD
IgE
IgG antibodies
monomer
most common
produced in large quantity upon second exposure
provides resistance against viruses, bacteria, and toxins
can cross placenta
IgM antibodies
pentamer (5)
first class produced upon initial exposure
forms immune complexes (agglutination)
IgA antibodies
dimer
in secretions
IgD antibodies
monomer
on surface of B cells as receptor
sensitizes or activates B cell upon antigen binding
IgE antibodies
monomer
on mast cells and basophils as receptor
triggers histamine release upon antigen binding
antigen-antibody complex
antibodies bind antigen via antigen binding sites
antigen gets bound by its antigenic determinant site (epitope)
epitope
the part of an antigen that is recognized by the immune system, specifically by antibodies, B cells or T cells
complete antigen
has two antigenic determinant sites
binds to both antigen-binding sites of variable segments of antibody
antibody-mediated immunity involves
the production of specific antibodies by plasma cells derived from activated B cells
B cell activation usually involves
antigen recognition, through binding to surface antibodies
costimulation by a Th cell
antibodies produced by active plasma cells bind to target antigen and:
inhibit its activity
destroy it
remove it from solution
promote its phagocytosis by other defense cells
autoimmune disorders
immune response targets normal body cells, auto-antibodies produced
immunodeficiency disease
immune system fails to develop, or immune responses are blocked
allergies
inappropriate or excessive immune responses to antigens
age related changes
thymus size decreases-> less T cells produced
decrease Th cells-> less B and Tc cell activation-> decrease immunity overall
decrease B cells-> decrease antibodies-> increase susceptibility to viral and bacterial infections
increase chance of cancer- decrease NK and Tc cells
