Immunology 1 Flashcards
Adaptive immunity
Slower on first exposure, specific. Cell mediated (T) and humoral (B).
Innate immunity
Rapid, nonspecific. E.g. physical barriers, cells (neutrophils, macrophages, dendritic cells), complement.
Passive immunity
Type adaptive immunity. Preformed Abs from source outside body. E.g. milk, antitoxins, Abs (HBV, rabies)
Active immunity
Type of adaptive immunity.
Body’s intrinsic mechanism to fight infection.
Lymphocytes, lymphoid organs
Primary lymphoid organs
Bone marrow, thymus.
Secondary lymphoid organs
Spleen, LNs.
Site of positive and negative selection of T cells
Starts in corticomedullary junction in thymus, continues until reaches medulla.
Embryology of thymus
3rd branchial pouch
Parenchyma of spleen
Red pulp and white pulp
White pulp (spleen)
Immune cell interaction. Central arteriole surrounded by PeriArterial Lymphatic Sheath
Red pulp (spleen)
RBC storage and turnover. Rich vasculature with splenic cords and fenestrated capillaries.
Marginal zone (spleen)
Separates red and white pulp.
Contains APCs.
Primary lymph nodes
Inactive follicles.
Stored lymphos awaiting antigen presentation
Secondary lymph nodes
Active follicles.
Pale germinal centers within cluster lymphos. B cells proliferate here and produce Abs.
Lymph drainage-stomach
Celiac
Lymph drainage-upper arm, lat breast
Axillary
Lymph drainage-duodenum, jejunum
Superior mesenteric
Lymph drainage-sigmoid colon
Colic -> inf. mesenteric
Lymph drainage-lower rectum and anal canal above pectinate
Internal iliac
Lymph drainage-anal canal below pectinate
Superficial inguinal
Lymph drainage-testes
Para-aortic
Lymph drainage-scrotum
Superficial inguinal
Lymph drainage-superficial thigh
Superficial inguinal
Lymph drainage-lat side dorsum foot
Popliteal
Cells of innate immunity
Phagocytic cells, APCs, NK cells
Phagocytes
Neutrophils
Macrophages
Dendritic cells
Antigen Presenting Cells (APCs)
Dendritic cells
Macrophages
B cells
NK cells
Contain lytic granules that attack and kill virus infected or tumor cells via antibody-dependent cellular cytotoxicity
Activation of classic pathway (complement)
C1 recognizes and binds constant fragment of IgG or IgM
Activation of alternative pathway (complement)
Activated C3 recognizes certain nonspecific antigens
Activation of lectin pathway (complement)
Mannose-binding lectin recognizes carbohydrate antigens on surfaces of microorganisms
C1 esterase inhibitor
Breaks apart C1.
Deficiency leads to hereditary angioedema, due to uncontrolled activation classic pathway
Decay Accelerating Factor (DAF)
Disrupts formation C3 convertase, thus halts complement.
If protein that associates DAF with RBC abnormal, can result in Paroxysmal Nocturnal Hemoglobinuria, as RBCs are more susceptible to complement-induced hemolysis.
C5b-C9 deficiency
Recurrent Neisseria infections
Deficiency in C3a, C3b
Recurrent pyogenic infections (respiratory tract)
Tc cells
CD8. Kills cells infected with viruses or intracellular bacteria
Main function of B cells
Recognize extracellular pathogens and differentiate into plasma cells that produce Abs
Functions of Abs
Opsonization
Neutralization
Complement activation
Antibody-dependent cellular cytotoxicity
MHCs
Encoded by HLA genes.
Most important molecules in transplantation
MHC I
On all nucleated cells
Present intracellular peptides
Binds TCR, CD8+ coreceptor
MHC II
On APCs
Present extracellular peptides (engulfed antigens)
Binds to TCR, CD4+ coreceptor
Hyperacute rejection
Preformed antidonor Abs. Minutes.
Acute rejection
Tc reaction with foreign MHCs. Reversible with immunosuppression, Weeks.
Chronic rejection
Ab mediated damage of vasculature. Irreversible. Months-years.
Graft v host disease
Irradiated immunocompromised host. Grafted T cells recognize body as foreign.
Rash, jaundice, diarrhea
CD3
Mature T cells. Assoc with TCR
CD4
Th. Coreceptor fo MHC II on APCs.
Coreceptor for HIV
CD8
Tc. Coreceptor for MHC I.
CD40
Isotype switching
CD28
T cell activation
CD19, CD20
B lymphocytes
CD21
Complement pathway, EBV receptor
IFN-alpha, IFN-beta
Signal cell to produce protein to decrease viral mRNA
IFN-gamma
Increases expression MHC I and II; stimulates phagocytosis by macrophages.
T cell activation
TCR binds antigen on MHC of APC, then costimulatory molecule required.
Isotype switching
Naive B cells express IgM but do not secrete Ab until activation and isotype switching occurs.
When IgM binds antigen, antigen peptides loaded onto MHC II. When that MHC II binds to TCR, CD4 + CD40, T cell produces cytokines which induce isotype switching
T cell anergy/tolerance-mechanisms
Positive selection (thymic cortex) Negative selection (thymic medulla) Peripheral tolerance by clonal deletion, anergy, active suppression, ignorance.
Positive selection
Ensures T cells that do not recognize self do not survive in periphery
Negative selection
T cells that react to self antigen deleted
Clonal deletion
T cell that binds repeatedly (e.g. high concentration of self antigen) leads to apoptosis
Anergy
Recognize self antigen but remains inactive due to lack costimulatory molecules required for its activation
Active suppression
Kept nonfunctional if self antigen at low levels-these differentiate into regulatory cells-secrete cytokines to prevent other cells from reacting to that antigens
Ignorance
If self reactive T cell never encounters its antigen–dies from lack of stimulation
B cell Anergy and Tolerance
Clonal deletion, Anergy, Clonal ignorance
Type I hypersensitivity-definition
IgE mediated. Immediate. Anaphylactic or atopic.
Type I hypersensitivity-examples
Urticaria, Allergic rhinitis, asthma, anaphylaxis
Urticaria
=Hives. Mildest form atopy. Histamine release leads to vasodilation and visible wheal and flare.
Type II hypersensitivity-definition
Antibody mediated. Activates complement.
Type II hypersensitivity-examples
Blood transfusions
Erythroblastosis fetalis
Goodpasture syndrome
Erythroblastosis fetalis
Rh- mother (sensitized) with Rh+ fetus. Mother’s antigens attack fetus, can cause brain damage.
Treated with anti-Rh IgG (RhoGAM)
Goodpasture
anti-GBM, which bind to type IV collagen. Ab complexes in kidney (leading to GN) and lung (leading to pulmonary hemorrhage).
Type III hypersensitivity-definition
Antigen-antibody complexes form when antigen is abundant. Immune complex deposits in tissues.
Clearance of infections creates antigen-Ab complexes
Some smaller complexes deposit in BV walls-they accumulate in endothelium (vasculitis) and synovium (arthritis)
Type III hypersensitivity-examples
SLE
Serum sickness
Arthus reaction
Serum sickness
When serum/Abs, e.g. horse antivenom, administered. +1 week–Abs to foreign proteins, leading to lymphadenopathy, fever, arthralgia, urticarial plaques.
Arthus reaction
Local swelling at site injection of antigen to which pt immunized. E.g. desensitization allergy shots
Type IV hypersensitivity-definition
Cell mediated (delayed). Initial exposure leads to memory cells. On repeated exposure, effector T cells drawn to site, proliferate, and activate macrophages.
Type IV hypersensitivity-examples
Tuberculin skin test
Contact dermatitis
B cell immunodeficiencies
Transient hypogammaglobulinemia of infancy
Bruton Aggamaglobulinemia
Dysgammaglobulinemia
T cell immunodeficiencies
Thymic aplasia (DiGeorge)
Chronic mucocutaneous candidiasis
AIDS
Combined immunodeficiencies
SCID
Wiskott-Aldrich syndrome
Hyper-IgM syndrome
Ataxia Telangiectasia
Transient hypogammaglobulinemia (of infancy)
Maternal IgG disappearing but infant’s B cells not producing sufficient quantities of Abs
Bruton agammaglobulinemia
X linked.
Defect in Bruton tyrosine kinase (B cell differentiation, maturation, signaling).
Low amts all Igs.
Recurrent extracellular pyogenic and enterovirus infections.
Tx: IVIG
Dysgammaglobulinemia
Defective B cell class switching. Most common type is low IgA, thus chronic lung infections (give Abx)
Thymic Aplasia (DiGeorge)
Hypocalcemia, tetany, no T cells
Defective formation 3rd, 4th pharyngeal pouches
Assoc with 22q11 microdeletions
Tx: thymic transplantation
Chronic mucocutaneous candidiasis
Lack of T cell reactivity (not number) to candida species
AIDS
Loss cell mediated (Th) immunity.
General wasting, constitutional sxs, opportunistic infections
SCID
Malfunctioning B and T cells. Deficiency in adenosine deaminase or purine nucleotide phosphorylase. X linked version most comm. Failure to thrive, chronic infections. Death within 1 year birth if untreated
Wiskott-Aldrich
X linked defect in WASP-defects in actin cytoskeleton.
Affects all hematopoietic cells, esp platelets, T cells.
Pyogenic infections, bleeding diathesis, eczema.
Increased risk AI disorders, lymphoma
Decreased IgM, normal IgA, IgG
Small platelets
Ataxia Telangiectasia
AR defect in ATM-insufficient response to DNA damage
Lymphocytes targeted due to high rate proliferation
IgA deficiency and malignancy
Cerebellar ataxia and telangiectasias
Most die mid 20s
Phagocyte Deficiencies
Leukocyte Adhesion defficiency
Chronic Granulomatous Disease
Chediak Higashi syndrome
Leukocyte adhesion deficiency
AR defect in integrin receptor, which helps phagocytes bind endothelium.
Bacterial infections WITHOUT pus
Chronic granulomatous disease
Defective NADPH oxidase, involved in ROS killing
Accumulation of immune cells in granulomas.
Infections with catalase positive bacteria or fungal infections.
Test: nitroblue tetrazolium dye.
Chediak Higashi sydrome
AR. Failure of vesicle fusion in neutrophils, platelets, melanocytes
Recurrent infections, esp strep and staph.
Increased bleeding, peripheral neuropathy