HS rxns, transplant, cell migration (Ben) Flashcards by Dustin O

Examples of Type III HS rxns

Ab-Ag complex mediated…

SLE - anti-RNP and anti-cardiolipin Abs
Rheumatoid Arthritis - rheumatoid factor Ab
Serum Sickness - Abs against anti-venom, etc.
Penicillin Allergy - binds to RBCs –> Ab binding
Arthus Reaction - local reaction to injected proteins

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Examples of Type II HS rxns

IgG against cell surface/matrix antigens…

Cytotoxic:

Rh incompatibility: erythroblastosis fetalis
Drug hypersensitivity: ex: penicillin –> RBC –> IgG

Non-cytotoxic:

Graves/Basedow: TSH-R Ab stimulates T3/T4 release
Myasthenia Gravis: anti-nAChR Ab

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Examples of Type IV HS rxns…

2-3 day delayed, T-cell mediated…

Contact Dermatitis: poison ivy complexes with skin proteins –> APCs activate T cells –> memory Ts react to poison ivy/skin complex quickly next time (also via Ni)
Multiple Sclerosis: T cells against myelin basic protein
Hashimoto’s: hypothyroidism, unknown thyroid Ag
Type I DM
Celiac: rxn against de-amidated gliadin

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5 results of complement activation

Lysis - via MAC formation
Opsonization - C4b/3b -> CR1-mediated phagocytosis
Inflammation - C3a/4a/5a anaphylatoxins
B cell activation - C3d binds CR2 on B cells
Immune Complex Clearance - RBCs carry C3b bound complexes to spleen/liver macrophages via CR1

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4 reasons ABO antibodies are produced under normal conditions

Previous contact with foreign blood
Maternal antigen exposure
Carbohydrate antigens of intestinal microbes
Exposure via plant pollens

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Describe “hyperacute rejection” of an allogenic graft.

(timescale, mechanism)

takes minutes - hours
usually occurs via ABO, HLA or VEC (vascular endothelial cell antigen) incompatibility
ex: endothelial cells express “allo-antigens” which are bound by host antibodies leading to complement activation, inflammation, endothelial damage + thrombosis

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What kind of cells are involved in host vs. graft rejection?

T cells (both CD4 + CD8)
NK cells
Macrophages

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Describe acute rejection against an allogenic graft.

(timescale, mechanism)

occurs up to 1 month after graft procedure
involves endothelitis in which IgG binds alloantigens on endothelium
delayed-type (IV) hypersensitivity occurs via CD4+ Th1, CD8+ cells + macrophages
causes intense parenchymal damage + interstitial inflammation
(no complement activation)

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Describe chronic rejection of an allogenic graft.

(timeframe, mechanism)

occurs months to years after the graft procedure
causes fibrosis and vascular sclerosis
due to a chronic type IV HS rxn, intimal SM cell proliferation will lead to vessel occlusion
(alloantigen-specific CD4+ cells release cytokines which cause SM prolif.)

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Describe the general procedure of a bone marrow graft.

Donor (usually family) gives marrow cells via pelvic marrow harvest procedure.
Recipient is treated with radiation and/or chemotherapy to achieve “cytoablation” (removal of their own cancerous marrow cells; also prevents HVG disease)
Marrow transplant is applied to recipient intravenously + the transplanted hematopoietic stem cells repopulate the marrow.

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What is apheresis?

How is it used in bone marrow transplantation?

removal of a certain component of the blood + return of the remaining components to circulation
can be used to remove HSCs from donor’s peripheral blood, rather than via painful pelvic marrow harvest
(2-3% peripherally circulating WBCs are stem cells)

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Name 3 molecules involved in the damage caused by Graft vs. Host Disease

All are CD8+ cell products…

TNF
FasL - binds FasR to induce apoptosis
Perforin-Granzyme system - perforin makes hole in membrane + granzymes enter to induce apoptosis

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List the target cells + organs of acute GVHD

mostly endothelial cells are damaged
main target organs are skin, liver, GI
(VEC (vascular endothelial cell) antigens are highly immunogenic –> when these cells are damaged + their antigens released, further damage occurs in surrounding tissues)

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What pathological changes are seen in chronic GVHD?

fibrosis and atrophy of tissues leading to loss of function
externally, skin color changes appear, showing up as spots on the skin

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What are 2 biological rejection suppression techniques?

Donor Selection - genotyping for immunological compatibility (family / internatn’l tranplant lists)
Ex Vivo Graft Manipulation - suppression of immune cells in graft

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What are 3 kinds of ex vivo graft manipulation?

Steroid Infusion - graft is infused with corticosteroids to downregulate MHC expression
Tolerance Induction - (no details on this…)
Antibodies - e.g. anti-CD28, anti-MHCII, anti-CD4

How does cyclosporin work as a pharmaceutical rejection suppression agent?

(What other drug works this way?)

blocks NFAT, a transcription factor for IL-2 (thus downregulation T cell proliferation)
(FK506 also works this way)

How do azathioprineandcyclophosphoamide work in pharmacological rejection suppression?

both block lymphocyte proliferation
(azathioprine via purine synthesis inhibition; cyclophosphamide mechanism is… less clear)

Other than the drugs already mentioned…

what are 3 methods for pharmaceutical suppression of graft rejection?

Monoclonal Abs - most aimed at T-cell depletion, such as anti-CD3 mAb
Corticosteroids - such as prednisone
Other anti-inflammatory agents

What are some (6) immunological changes seen in pregnancy?

(too much for one card… just an overview)

Th2 shift
HLA-G - a non-classical HLA expressed on fetal-derived placenta cells
Blocking antibodies - bind antigens without inducing immune response, block other Abs from binding
Decrease of CD8+ cells
hCG and IL-6 release from placenta + female GU tract
PIBF - leads to incr. IL-10 and decr. NK cells

What role do trophoblast cells play in the fetal antigen presentation + gestational immune tolerance?

have no MHC-II
have monomorphic MHC-I-like HLA-G/E molecules which:
- don’t present to CD8+ cells
- block NK cells (normally activated by MHC-I absence)

What cytokines + cell types (2) are important in immunosuppression during pregnancy?

Th2 cytokines - block Th1 type rxns against fetus
TGF-beta - multiple suppressive effects
Treg - CD4+/CD25+ cells
gamma-delta-T cells

What important transcription factor is expressed by Treg cells in the decidua during pregnancy?

Foxp3

When during pregnancy are Treg levels highest?

(this is probably not necessary, just showed up on a graph in lecture, but wasnt mentioned)

Treg levels rise slowly to a peak around week 10-11 and then decline slowly again until birth

how are pregnancy-related Tregs created? from what kind of cells? what general role do they play? (also not super important... just seen in a lecture figure)

* naive **CD4+ cells** become Tregs * presentation of **paternal alloantigens** to CD4+ induces differentiation into "**pTreg**" cells (p=pregnancy?) * pTregs ensure embryo/fetal tolerance and vascularization

Aside from pTregs, what other kind of cell is important in gestational immune tolerance? Name 4 mechanisms by which they promote tolerance (less important than just the cell type, also from a lecture figure)

**gamma delta T cells** - leave thymus without CD4 or CD8 + present in placental mucosa * suppression + cytolysis of effector Ts * secrete Th1 antagonizing cytokines * cytolysis of APCs * block neutrophil infiltration

What three sources provide immunosuppresive _hormones_ during pregnancy? What are the hormones?

1. Maternal - **progesterone + estrogen** 2. Placental - **hCG** 3. Fetal - **alpha-1-fetoprotein**

What important molecule is stimulated by a _maternal hormone_ during pregnancy and contributes to numerous mechanisms for gestational immunosuppression? What mechanisms (5)?

**PIBF** - progesterone-induced blocking factor * inhibits NK cells * increases Th2 cytokines * has "anti-abortive" effects * inhibits arachidonic acid metabolism * increases _asymmetric Ab_ synthesis

What are **assymetric antibodie**s?

Abs that have an extra glycosylation in the Fab region, causing them to be "blocking antibodies" which bind antigen but do not activate effector mechanisms

What is the difference between chemotaxis and chemokinesis?

* Chemotaxis is _vectorial_ meaning it has a specific direction * Chemokinesis is _random_, without specific direction

What is **haptotaxis**?

* chemotaxis in which the attractant is _bound to a surface_ such as the extracellular matrix * ex: axonal outgrowth based on the conc. gradient of adhesion sites

What are 4 kinds of "professional" chemoattractants?

* **chemokines** (CC and CXC family) * **C3a** and **C5a** ("anaphylatoxins") * **bacterial N-formyl peptides** (FP) * **arachidonic acid products**

What are the 4 classes of chemokines + an example of each? (examples not that important, except one)

* **CC** - "RANTES"/CCL5 - eos-/baso-/T cell attractant * **CXC** - CXCL8/**IL-8** - mostly from macrophages to attract neutrophils * **CX3CL** - "fractalkine" * **C** - "lymphotactine" - attracts T cells

Describe the **3 chamber technique** for evaluation of chemotactic agents.

* agarose plate with 3 sets of wells * in one set, place attractant; in another place cells; in third place neutral control substance * measure the "diameter" of the movement of the cells toward the attractant (d_A) and control (d_C) * d_A\> d_C if tested substances is true chemoattractant

Describe the **2 chamber method** for evaluating chemoattractant strength.

* one chamber = cells * other chamber = chemoattractant * between them = semi-permeable membrane * after some time, can count # of cell that migrated across membrane to chemoattractant

In assays of _transendothelial migration_ ... what is the difference between _direct_ and _reverse_ TEM assays?

* **direct** - migrating cells placed directly on endothelial cell layer, with filters btwn endoth. + chemoattractant * **reverse** - cells placed directly on filters with endothelial cells below (measures what conc. of chemoattractant needed to "pull" cells thru filter to endothelium)

How are migration assays performed on the wall of a cell culture flask?

* coat one side of the flask with **ECM peptides** * load cells onto bottom of flask + let them adhere (24 h) * tilt flask and wait 1-10 days as cells culture + migrate * can measure migration of cells along ECM peptide layer

Describe the "**matrigel**" technique for in vivo cell migration measurement.

* a gel disk containing chemoattractant (+ sandwiched btwn a thick and thin filter) is inserted into a test animal subcutaneously * wait 5-10 days to allow cell migration to occur * remove disk, wash with NaCl, fixate + evaluate amt of cells which have migrated into it

How can **sephadex beads** be used to measure in vivo cell migration?

* inject chemoattractant-infused beads into test animal peritoneal cavity * wait 6-48 hrs * observe granulocyte/monocyte migration into peritoneal cavity + presence of cytokines (LTB4, TNF-a, IL8)