Immunology wk 3

Rag 1 and Rag 2

TdT

Dendritic cells take up bacterial antigens and process them.  If PAMPs are detected, mature, change expression to be a better APC, enter draining lymphatic vessel, move to lymph node and settle in paracortex, look through 5,000 T cells in an hour.  T cells enter LN via blood, if they match the DC they become activated and proliferate, differentiate.

• See antigen displayed by molecules (MHC) on SURFACE OF CELLS (not circulation)
• CD4 ONLY recognize correct antigen presented by MHCII on Dendritic Cells, B cells or Macrophages.  
• 3 signals: 1 from TCR/peptide, 2 from CD28/B7 (costimulation is the "safety"), 3 are cytokines from APC in lymph node - this determines Th1 vs Th2 vs Th17.  Only ALL THREE will activate, otherwise anergy or no effect.

• TCR recognizes Ag
• CD3 proteins associate with alpha/beta chains.  All four have trans-membrane ITAMs (Immunoreceptor tyrosine-based activation motif).  
• Antigen binds, increasing phosphorylation of ITAM, triggers intracellular signaling cascade, biochemical intermediates, enzymes, activation of transcription factors (NF-kappaB, NFAT, AP-1) to regulate gene expression

on naive T cell, binds to B7 on MHC to increase affinity of TCR for MHC and lower threshold of activation.  Otherwise 100% of APC surface molecules would have to be bound to same antigen, now 0.1-1%

area of contact between two cells (like T cell and APC).  Outer ring is adhesion molecules, inner ring is TCR/MHC and CD28/B7

• T-cell autocrine growth factor (released by activated T to bind to T) stimulating proliferation and clonal expansion (HUGE expansion, 50% specific for same peptide/MHC complex).
• Naive T cells express low affinity IL-2 receptor (beta, gamma chains).  Activated T cells upregulate alpha so they can express high affinity IL-2 receptor
• IL-2 signaling is a target for lots of immunosuppressive drugs (like cyclosporine, tacrolimus decrease production, Rapamicin inhibits receptor)

Cross-linking of CD28 (co-stimulation) induces expression of CTLA-4.  It has higher affinity for B7 than CD28 does, so it binds and delivers inhibitory signals (downregulates IL-2) to activated T cells, which stop proliferating and die from apoptosis

• activate B cells to produce antibodies to eliminate extracellular microbes
• promote differentiation of cytotoxic T lymphocytes to kill infected cells
• Activate macrophages to kill phagocytosed microbes or repair tissues
• promote migration and activation of inflammatory cells like granulocyte eosinophils and monocyte/macrophages.

subpopulations of CD4 T cells (and macrophages, probably more) mediate different responses.  Pluripotent at first,but progressive activation leads to more limited cytokine expression, can't go back

• cytokine: interferon gamma (IFNγ)
• immune: macrophage activation, IgG production
• Host defense: intracellular microbes
• role in disease: autoimmunity, tissue damage with chronic infections

• Cytokines: IL-4, IL-5, IL-13
• Immune: mast cell, eosinophil activation; IgE production, alternative macrophage activation
• host defense: helminthic parasites
• role in disease: allergic diseases

• Cytokines: IL-17A, IL-17F, IL-22
• Immune: neutrophilic, monocytic inflammation
• host defense: extracellular bacteria, fungi
• Role in disease: autoimmunity

• Naive can become any other (1, 2, 17)
• APC produces cytokines (SIGNAL 3 of activation) to bias a cell toward what is needed.  
• Induction: subset specific transcription factors elicit production of subset-specific cytokines.  
• commitment: epigenetic modifications that facilitate subset-specific cytokine production
• amplification: cytokines produced by T cells promote development of more of same subset

• induction: IL-12 and IFN-y, elicited by intracellular microbes (from macrophage, NK cell)
• Commitment: T-bet (transcription factor stimulated by IFN-y)
• Amplification: T-bet causes production of IFN-y
• IFN-y causes macrophage activation and production of some antibodies.

• Induction: IL-4 elicited by helminths or allergens (from mast cells, eosinophils)
• Commitment: Gata-3
• Amplification: IL-4
• IL-4, IL-5, IL-13 cause IgE production, Eosinophil activation and mucus production

• Induction: IL-6, IL-1 and IL-23 elicited by extracellular bacteria, fungi (from Dendritic cells, maybe also TGF-beta?)
• Commitment: ROR-gamma-T
• Amplification: IL-21
• produces IL-17 and IL-22 - Inflammation (neutrophils), barrier functions

cytokine that causes T cells to become Th1 cells (also in amplification).  Stimulated by intracellular microbes from natural killer cells.  Also causes macrophage activation and production of some antibodies.

• Elicited by helminths or allergens from dendritic cells, mast cells, maybe eosinophils. Induces development of Th2 cells (also involved in amplification).  
• All three cause IgE production, eosinophil activation, mucus production.

produced by Th17 cells, cause inflammation (neutrophils) and barrier functions.

• Classical macrophage activation (enhanced microbial killing).  Activates macro with INFy, which respond by 1. killing phagocytosed bacteria, 2. secreting cytokines (TNF, IL-1, IL-12, chemokines) and 3. increasing expression of MHC and costimulators (B7 molecules)
• Complement binding and opsonizing IgG antibodies
• Chronic Th1 response can cause granulomatous inflammation (Th1 produces TNF to extravasate monocytes, IFNy to differentiate, and form a fibroblast circle around macrophages, activated macrophages, lymphocytes and a center giant cell).
• autoimmune and systemic inflammatory diseases like diabetes, multiple sclerosis, rheumatoid arthritis, via activation of macrophages and harmful antibodies

• antibody production (IL-4 tells B cell to make IgG and IgE)
• Mast Cell degranulation caused by IgE
• Intestinal mucus secretion and peristalsis (IL-4 and IL-13)
• Eosinophil activation (IL-5)
• Alternative macrophage activation (tissue repair) (IL-4, IL-13)
• Atopic dermatitis in dogs from predisposition to make Th2 (etiology complex, but un-activated skin has more Th2 than it should)
• allergies and asthma via activation of eosinophils and IgE responses

• Classically activated macrophages (M1) are activated by Microbial TRL-ligands and interferon gamma (IFNy, Th1).  Phagocytosis and killing bacteria, fungus (ROS, NO, lysosomal enzymes), Inflammation (IL-1, IL-12, IL-23, chemokines)
• Alternatively activated macrophages (M2) are activated by IL-13, IL-4 (Th2) and have anti-inflammatory effects, wound repair and fibrosis (IL-10, TGF-beta).

• Inflammation, neutrophil response and anti-microbial peptides via leukocyte and tissue produced chemokines, TNF, IL-1, IL-6, CSFs (stimulated by IL-17)
• increased barrier function and anti-microbial peptides via tissue via IL-22
• mutations cause Job's syndrome (deficient Th17 = increased susceptibility to extracellular bacteria and fungal infections
• rare autoimmune disease associated with anti IL-17 and anti-IL-22 autoantibodies linked to chronic mucocutaneous candidiasis (CMC)
• organ-specific inflammatory disease (psoriasis, IBD) via mobilization of neutrophils, monocytes

• 90-95% apoptose when they stop receiving survival signals from TCR (5=10% are memory), but persistent infections need more regulation
• T regulator cells: CTLA-4 on Treg removes B7 from APC so they can't costimulate as well
• T regs secrete inhibitory mediators like IL-10, TGFbeta to dampen immune response of DCs, Macrophages, T cells.  
• T regs consume all the IL-2 growth factor so no one else can use it.

• Thymic (natural): induced by self-antigens in thymus during development (born as T regs).  Reside in peripheral tissue to limit autoimmunity
• peripheral (induced/adaptive): induced by antigen exposure in the periphery (conventional CD4 cells that become Tregs).  May involve IL-2 and TGF-beta.  
• generated in all immune response to limit collateral damage.

most autoreactive T cells are eliminated in thymus via negative selection (but not all)

some rogue autoreactive T cells make it to periphery and need to be suppressed by Tregs.

• secondary have pale germinal centers of B cells undergoing clonal expansion.  Sites of class switching and affinity maturation.  Also include macrophages that eat the apoptotic debris of the ones that don't make it ("tingible body" macrophages).  Contain FDCs.  
• A corona or mantle of T cells is around the germinal center of cells that don't have the right affinity.

either macrophages (professional phagocytes) or dendritic cells (professional APCs)

APC in paracortex (aka).  Related to langerhans cells of skin and mucosal epithelium.  Stimulated langerhans cells travel to regional LN, stay a while (immunologic memory).

• Follicular hyperplasia: appearance of large follicles with prominent germinal centers.  Typical of certain bacteria or autoimmune, means a primarily B cell response.  Extreme in prolonged intense antigenic situation (FIV-lentivirus, lyme)
• (Follicular sclerosis): hypocellular follicular centers full of eosinophilic ground substance in follicular hyperplasia, "burn out" of germinal center from prolonged stimulation.
• Paracortical hyperplasia: may encroach on follicular areas, T-cell blasts and tingible body macrophages (apoptosis eaters) can cause "starry sky".  HEV prominent.  Primarily T cell response (virus or vaccine).  
• Sinus hyperplasia/histiocytosis: cortical and medullary sinuses expanded by histiocytes/macrophages after draining chronic problem, due to increased antigen load.  Macrophages may have phagocytic debris.  
• lymphadenitis: infectious agent localizes in lymph node or inflammatory cells/fluids drain there.  Will also be some hyperplasia (or inflammatory destruction). Acute (hyperemia, pain, heat, edema) vs chronic (LN enlarged and firm, fibrosus, less heat/edema).

• lymphomas: generalized lymphadenopathy, firm, nonpainful, fixed LN (infiltration). Diffuse sheet of uniform lymphocytes replacing normal architecture.  T cell is worse than B cell.  15% cause hypercalcemia (CD4+)
• leukemias: lymphoid or myeloid hematopoietic stem cells originating in bone marrow. usually hepatosplenomegaly.  Invade cords, trabeculae and paracortex, then take over whole thing.  
• histiocytoses: include canine cutaneous, cutaneous, systemic, histiocytic sarcoma.   
• often sites of secondary metastasis (stage LN to stage cancer)

surround splenic arterioles, full of T cells.

between red and white pulp of the spleen

there are efferent, but no afferent.  Antigen gains access to red and white pulp via marginal zone.  "in-line" filter of blood that is protected from exposure to antigen.

• macrophages defend against bacterial sepsis via opsonized phagocytosis (Fc and complement fragment receptors)
• maturation of reticulocytes
• pitting of erythrocytes
• removal of senescent cells
• storage of erythrocytes and platelets so contraction causes "autoinfusion"

• 60-80% are CD8 (most of PALS are CD4).  
• splenic gamma-delta T cells and NK cells are in red pulp almost exclusively.

sheltered from antigen by innate immune system, and regional lymph nodes and Kupffer cells filter really well, so this indicates SYSTEMIC ANTIGENEMIA.

• is a diseased spleen.  
• Makes it prone to thrombosis and infarction
• Pulpy (passive splenic congestion/increased blood) vs meaty (increased cells)

• effector CD8+ T cells: kill infected "target cells", activate macrophages
• Memory cells
• both in peripheral tissues

• Signal 1: antigen recognition
• signal 2: costimulation (ONLY for activation, otherwise unnecessary) B7 + CD28
• signal 3: cytokines (IL-12 or type I IFNs)
• just like CD4+ (but 3 is IL-12 for Th1, IL-4 for Th-2, IL-6, IL-1, IL-23 for Th17)

• Dendritic cell MHC I, antigen found in cytosol.  
• Cross-presentation required for viruses that don't infect dendritic cells but require CD8 for clearance

viruses don't infect dendritic cells but DC must display on MHC I (cytosolic) to activate CD8, so viruses are phagocytized, degraded in cytoplasm and sent to MHC I.

• promote further maturation of APCs to enhance their ability to stimulate CD8+
• produce IL-2 to enhance CD8 T cell proliferation)

• recognize peptides on infected (and tumor) cells and kill them directly
• secrete IFN-y to enhance macrophage's ability to destroy phagocytosed bugs

• Adhesion molecules (I-CAMs) anchor CD8 to target cell (nonspecific adhesion)
• specific recognition/TCR engagement polarizes CD8 cell, redistributes cytoplasm and cytoskeleton.  
• Lytic granules (perforin = pore and granzyme = apoptosis) are released at site of cell contact.
• Activates nucleases to cleave DNA, cell disintegrates from within by shedding membrane bound vesicles.  Macrophages eat corpse.  
• Generate new granules.  Kill 2-16 virally infected cells a day
• Can team up or cooperate with other CD8

• 90-95% die
• 5-10% become memory to mount an accelerated 2nd response

more memory T cells than naive T cells, more easily activated (no co-stimulation needed and sensitive to cytokines)

• CD4: 8-12y half life
• CD8: 8-15y half life
• vaccines can be protective for 75y+

• central memory T cell: localized in lymphoid tissue, highly proliferative.  
• effector memory T cell: localized in peripheral organs, high levels of effector molecules

• increase in numbers of memory CD8 T cells over time
• highly differentiated bu fully functional