Appunti completi esame di Pathogenetic bases of diseases

CLINICAL MANIFESTATIONS

It depends on the vascular site where the occlusion occurs. It depends on whether it’s venous

thrombosis or arterial/cardiac thrombosis. Three main clinical manifestations:

1. deep venous thrombosis (DVT)

2. arterial and cardiac

3. disseminated intravascular coagulopathy (DIC)

DIC

The most severe clinical signs of systemic inflammation (when IL1/TNF levels exceed the

threshold) are due to the effect of proinflammatory cytokines on:

- the heart: decreased myocardial contractility (cardiomyopathy)

- the vascular system: decreased systemic resistance

- the liver: perturbation of metabolism and hyperglycemia

- the coagulation system: disruption of the coagulation homeostasis, with coagulopathy,

ranging from fall in platelet count

It’s a condition associated to massive intravascular activation of thrombin. It’s the widespread

formation of thrombi in the microcirculation. Thrombosis consumes coagulation factors and

platelets, leading to consumptive coagulopathy. Thus, the first thrombotic symptoms can evolve

into a bleeding catastrophe (hemorrhagic stroke or hypovolemic shock).

IMMUNOTHROMBOSIS

The process whereby immune inflammatory mediators (immune) activate hemostasis

(thrombosis). If uncontrolled, immunothrombosis evolves into thrombosis, a pathological

condition, in which leukocytes play an active role. Immune modulation could be used for vascular

prevention of pathologic conditions (deep venous thrombosis), with a lower risk of bleeding

complications than conventional therapeutic approaches.

EVOLUTIONARY EXPLANATION OF IMMUNOTHROMBOSIS

The link between inflammation and coagulation is an evolutionary response meant to defend

from entry and spread of pathogens. Evolutionarily, blood coagulation served both the functions

of preventing blood loss and defending from microbes (contributing to the production of

antimicrobial peptides). Wounds represent a port of entry for pathogens, thus, hemostasis can

serve the important function of “defense from infections”. This is why hemostasis and

antimicrobial defenses converge.

IMMUNOTHROMBOSIS IN AN ARTHROPOD

The link between coagulation and immune response has been suggested by studies of the blood

of ancient invertebrates.

Limulus polyphemus: horseshoe crab, origin traced back 400 millions years. One of the oldest

classes of marine arthropods. Blood (hemolymph) contains amebocytes, similarly to red blood

cells, containing granules rich in clotting factors. Upon encountering endotoxin, the amebocytes

clot.

The Limulus Amebocyte Lysate test (LAL)

LAL, also known as Bacterial Endotoxin test, is a highly sensitive test used to detect or quantify

bacterial endotoxins, byproducts of Gram negative bacteria. The test is based on the property of

amebocyte lysate from the horseshoe crab (Limulus polyphemus) to mediate blood clot in the

crab when in contact with endotoxins. Amebocyte extract is commercially prepared and used as

reagent to measure endotoxins in human and animal injectable drugs, biological products, and

medical devices. It prevents the administration of products or drugs which may cause fever and

endotoxic shock.

LINK BETWEEN HEMOSTASIS TO IMMUNE RESPONSE

Four pathways link hemostasis to immune response:

- procoagulant effect of systemic inflammation

- the Complement cascade

- leukocyte recruitment into the clot

- leukocyte activation by platelets

Procoagulant effect of systemic inflammation

Acute phase proteins → proteins whose concentration in blood varies of at least 25% during an

inflammatory response.

How: Mainly released by the liver, after IL-6 stimulation.

Why: Take part to the inflammatory response.

Who: The most important are C reactive protein (CRP), fibrinogen, serum amyloid A (SAA)

→ Erythrocyte sedimentation rate (Velocità di eritrosedimentazione (VES)) →it reflects the

variation in plasma proteins, mainly fibrinogen, which takes part in the coagulation process.

Fibrinogen binds to erythrocytes and cause them to form stacks that sediment more rapidly than

erythrocytes. The time of variation of ESR (VES) is 24-48 hours post inflammatory response, thus

the ESR does not reflect the beginning of inflammation and persists after the acute inflammatory

response is over. Normal values of ESR vary according to age and gender.

Complement cascade

Classical pathway, lectin pathway and alternative pathway converge on the complement cascade

which leads to_

- leukocyte recruitment

- pathogen opsonization

- pathogen killing

Coagulation Factor XII can activate the classical complement pathway, via C1.

Thrombin can function as a C5 convertase, in a C3-independent manner.

C5a induces expression of tissue factor by mononuclear cells.

Leukocyte recruitment to the clot

Both neutrophils and monocytes are rapidly incorporated into growing clots.

The trigger for leukocyte recruitment varies depending on the stimulus that triggers thrombosis.

In arterial thrombosis, leukocytes are recruited under high-shear conditions, supported by

platelets via expression of P-selectin.

In venous thrombosis, the endothelial cell wall adopt a pro-inflammatory phenotype.

Platelet expresses molecules that make them interacting with leukocytes.

Leukocytes activate thrombosis:

1. In response to PAMPs or DAMPs, monocytes deliver intravascular tissue factor,

triggering the extrinsic pathway at the site of pathogen exposure

2. Neutrophils act via NETs, by directly activating Factor XII (negatively charged surface of

NETs) and inhibiting the action of coagulation inhibitors

Key factor: Intravascular Tissue Factor

1. In physiological conditions, no TF activity in blood

2. During thrombosis, mostly delivered by myeloid cells (not much endothelial cells and

platelets)

3. Binds Factor VII and then Factor X, then activates coagulation

Platelets activate leukocytes

1. Platelets have PPRs to detect PAMPs, then after the encounter with blood-born

pathogens

2. Release of many chemoattractants

3. Induction of microbicidal activity in phagocytes

4. Dendritic cell maturation

ANTIMICROBIAL ACTION OF IMMUNO-THROMBOSIS

1. Fibrin entraps pathogens (mice lacking fibrinogen succumb prematurely to pathogen

infection)

2. Prevention of pathogen spreading and increased pathogen recognition

3. Leukocytes within the clot and platelets exert antimicrobial activity

4. Generation of inflammatory mediator

IMMUNOTHROMBOSIS IN CANCER

Link between cancer and coagulation:

- Tumor cells are proinflammatory, proangiogenic

- Tumor cells adhere to and activate the endothelium, they are pro-thrombotic

- Tumor cells secrete TF, they are pro-coagulant

- Fibrin clots protect circulating cancer cells from attack by the immune system

Link between cancer and venous thromboembolism (VTE)

1. Clinical association between VTE and occult malignancy (Trousseau, 1865)

2. 50% of patients with cancer have thrombosis (post-mortem)

3. Cancer is associated with a hypercoagulable state and a four-fold increase in thrombosis

risk

4. Major risk factors for VTE in cancer patients:

- tumor type (brain, hematological, PDAC)

- clinical stage

- type of surgery

- type of therapy (chemotherapy, anti-angiogenic: thrombosis is an important

complication!!)

- insertion of central venous catheter

- individual factors (gender, age, obesity)

We have:

- extrinsic pathway:

a. venous compression by locally advanced tumors

b. vessel damage by medications

c. bed rest

d. systemic inflammation

- intrinsic pathway → oncogenic events (MER, PTEN, K-Ras, p53)

Both lead to pro coagulation state which lead to cancer related thromboembolism.

PATHOGENETIC BASIS OF DISEASE

Sfondrini

TUMOR IMMUNOLOGY

Tumor cells have the characteristic of growing in an uncontrolled manner, of invading normal

tissues and often of metastasizing, ie growing in areas distinct from the tissue of origin.

Many tissues keep replicating, sometimes some cells gain mutations. Normally there are

mechanisms to repair this alteration, if not there is apoptosis. The tumor normally derives from a

single cell that has undergone a neoplastic transformation→ monoclonal origin.

IMMUNOSURVEILLANCE (Burnet ‘50)

The immune system is able to recognize and eliminate abnormal cells before they can form a

tumor.

This idea has been supported by many observations:

- experimental results with transplanted tumors or carcinogen-induced tumors →1775

Percival Pott observed the high incidence of scrotal cancer in chimney sweeps (aromatic

hydrocarbons in the soot: effects of mandatory washing → discover of carcinogens)

- the presence of lymphocytic infiltrates around tumors and reactive changes in lymph

nodes draining sites of cancer. The presence of lymphocytic infiltrates correlate with

good prognosis in some tumors.

- the increased incidence of some cancers in immunodeficient people and mice;

- the direct demonstration of tumor-specific T cells and antibodies in patients

(spontaneous regression in melanoma or thymoma);

- most recently, the response of advanced cancers to therapeutic agents that act by

stimulating host T-cell responses

EXPERIMENTAL RESULTS WITH TRANSPLANTED TUMORS

→Tumors can induce an immune response

We induce a tumor in a mouse, then we resect the tumor and transplant some tumor cells in the

same mouse → no tumor growth. If we transplant the same tumor cells in a naive mouse we have

tumor growth. If we transplant tumor cells and CD8 T cells isolated from the original mouse in a

naive mouse we have no tumor. This experiment demonstrates that tumors can give an immune

response.

Human spontaneous tumors normally express few non-self antigens and are generally not very

immunogenic.

PRESENCE OF LYMPHOCYTIC INFILTRATES AROUND TUMORS

Data suggests that tumor infiltration of cytotoxic (CD8+ ) T cells is associated with favorable

prognosis.

INCREASED FREQUENCY OF CANCERS IN THE SETTING OF

IMMUNODEFICIENCY

High incidence of tumors after immunosuppressive therapies and in patients with acquired or

congenital ID.

AIDS patients show an increased incidence of malignancies (Kaposi’s sarcoma, non-Hodgkin B-

cell lymphoma).

TUMOR ANTIGENS

While microbes have a different DNA from our cells and express completely different proteins;

tumor cells derived from a self cell and thus have very few differences, so in general the tumors

are not very immunogenic → absence of danger signal.

- tumor specific antigens on tumor but not on normal cells → these antigens can be

involved or not in tumor growthing

- tumor associated antigens also expressed on normal cells, but expressed at higher level

on tumor cells

We can have:

- mutated self protein: various mutant protein in carcinogen or radiation induced animal

tumors, we have various mutated proteins in melanomas

- product of oncogene or mutated tumor suppressor gene:

a. oncogene products: mutated Ras, Bcr/Abl fusion proteins