Scarica Pathological Processes and Inflammatory Responses - Prof. Capucchio e più Dispense in PDF di Patologia solo su Docsity!
Programme ➢ Basic concepts of pathology: definition of homeostasis and disease; mentions of inflammation (acute and chronic inflammatory disease), degeneration and pathological growth ➢ Pathophysiology of gastrointestinal tract ➢ GI pathology by most important agents affecting large and small animals ➢ GI pathology induced by diet change and secondary systemic changes ➢ Diagnostic methods used by the pathologist ➢ Interpretation and discussion of histological slides with the most common injuries reported during the frontal lessons BASIC CONCEPTS OF PATHOLOGY Who is the veterinary pathologist? A medical detective who must recognize diseases in animals. 2 branches of veterinary pathology:
- anatomical pathology → concerned with the analysis of the organs, tissues or the whole bodies (lesions) of the animals to diagnose a disease
- clinical pathology → deals with the examination of body fluids such as blood, urine, cavity effusions or tissue aspirates to diagnose a disease The aim is:
- to investigate cell and tissue responsible to injury
- to identify the cause (etiology) of injury
- to understand the mechanism of the disease → pathogenesis
- to make a correct diagnosis → to assign name to a disease Disease A disease is a structural and functional change (alteration) of a cell, tissue or organ that alters homeostasis of the organism producing specific clinical signs. Homeostasis is the ability of the body or cell to seek and to maintain a condition of equilibrium or stability within its internal environment when dealing with external changes. A morbid state is a local abnormality. Pathogenesis Genesis → origin or development Pathogenesis is the sequence of events that leads from the cause of the disease to structural and functional abnormalities, to how the disease manifests itself and finally to the resolution or recovery of the disease. For example → common respiratory infection:
- cause → exposure to cold, virus
- incubation time → virus multiplies into cells
- manifestations → host begins to have symptoms (virus induces cell damage)
- recovery → return to previous state (immune response of the host wins the virus) Causes of disease → etiology ● exogenous → external for example trauma, chemical injury, microbial infections ● endogenous → internal for example immunological reactions, abnormal metabolism
● idiopathic → cause of the disease never discovered (unknown etiology) ● predisposing → factors which make an individual more susceptible to a disease (poor ventilation, cold etc) Exogenous : ➢ physical → trauma, cold, heat, electricity, radiation, pressure ➢ chemical → toxins (biological, environmental), drugs ➢ biological → virus, bacteria, protozoa, fungi, metazoa, prions ➢ nutritional → deficits or overheatings of some factors like vitamins, minerals, elements Example of pathological process Farm: 75 Piedmontese cows Food: hay, home produced cornmeal 6 calves, 6-15 months old: neurological signs compatible with intracranial localization, weight loss, dysorexia, reduced ruminal activity, CSF normal. Blood exams: ipoalbuminemia, increase in AST and CPK. Clinical diagnosis → suspected prosencephalic pathology. Death of 3 calves. All consumed cornmeal. Autopsy:
- gross examination → in the liver, there’s severe hepatopathy with fibrosis, degeneration of the cells, steatosis and necrosis; in the brain, there’s edema of the white matter at the junction between the white and the gray matter, petechiae, multifocal necrotic neurons
- morphological diagnosis → hepatopathy and encephalopathy Toxicological exams → in the cornmeal, there’s a presence of toxins (15 ppm fumonisins, 1400 ppb aflatoxin B1, 120 ppb aflatoxin B2, 80 ppb aflatoxin G1 and 70 ppb aflatoxin G2). Liver samples: 0·3 and 0·6 ppb total aflatoxins.
Chemical fixation → Aldehyde compound (non-coagulant fixing agents formingwith proteins intermolecular and intramolecular cross-links resulting in a better retention of the cellular organization) 10% neutral buffered formalin (Bouin, Carnoi). Physical fixation → cryofixation, quality of fixation sometimes not ideal or poor, damage to cells by ice crystal formation. Rapid plunging into either liquid propane or isopentane pre-cooled at -180° to -190°C in liquid nitrogen. The aim is to keep the cellular components as “lifelike” as possibile, it’s essential that all biochemical and proteolytic processes are inactivated and structures are immobilized and locked in space by “fixation” step.
4. Histochemistry → to study the chemistry of the tissue for example glycogen, lipids, mucin etc
5. Immunohistochemistry → to employ antibodies like immunoglobulin with antigen specify to visualize substances in tissue sections or cell preparation 6. Electron microscopy → to study disorders at the organelle level or to demonstrate the biological agents presence in tissue samples 7. Molecular pathology → to identify alterations of the molecules or genome of the tissue PCR → amplification of tiny quantity of nuclei acid I n situ hybridization → localization of a specific DNA or RNA sequence in a tissue section using a labeled complementary DNA/RNA Western blot → detection of specific proteins in tissue homogenate
Players of the inflammation Many players are involved in an inflammation like:
- endothelial cells
- circulation cells → neutrophils, eosinophils, basophils, lymphocytes, monocytes, platelets - circulating proteins and local proteins
- connective tissue cells → mast cells, macrophages, fibroblasts
- extracellular matrix → proteins, proteoglycans, glycoproteins Acute inflammation An acute inflammation can be due to: 1) bacterial/viral/parasitic infections and microbial toxins
- trauma (blunt and penetrating)
- physical and chemical agents → thermal injury, burns or frostbite, irradiation, some environmental chemicals 4) tissue necrosis
- foreign bodies → splinters, dirt and sutures
- immune reactions (also called hypersensitivity reactions) Acute inflammation has 2 main phases: a) vascular changes → alteration in the vessel caliber resulting in increased blood flow (vasodilation) and structural changes which permits plasma proteins to leave circulation (increased vascular permeability) b) cellular events → emigration of leukocytes from the microcirculation and accumulation in the focus of injury (cell recruitment and activation) In this image, you can see the changes on the capillary level → there is a dilation of the vessel, migration of fluids, proteins from the blood to the extracellular space.
The migrations of these cells involved several mediators that permit adhesion of leukocytes to endothelium and followed the migration through the intercellular junction until to reach the interstitial where can be present the cause of the injury for example bacterial infection. Firstly, there’s a dilation due to activation of the endothelial component → vasodilation that increase in blood flow, then there’s an activation of endothelial cells which modify the intercellular junction to permit of extravasation of proteins before and after leukocytes (like neutrophils, DCs, NK cells etc). This is an histological picture which shows the adhesion and migration of neutrophils through endothelium where they phagocytize the pathogens.
All acute inflammation can have a different evolution. An acute inflammation can progress and become a chronic inflammation or can produced CV damage or can repaired with a scar or resolution (restitutio ad integrum). So the solutions of an acute inflammation process are 3:
**1. chronic inflammation
- destruction of a tissue repairing with a scar
- resolution** All inflammatory processes are characterized by the production of exudate → the fluid that moves from vessels to interstitium. Which are the main components of exudation? The exudate is composed of water, ions, plasma proteins and circulating cells (leukocytes).
Morphological patterns of an inflammation An acute inflammation can show different morphological patterns: 1) Serous inflammation is the first form of inflammation, it’s characterized by minimal permeabilization, its exudation is clear and fluid and mainly composed by water, small quantity of proteins with slow molecular weight and a few cells (generally neutrophils). It’s observable on the skin at the level of serous membranes. Pleuritis, pericarditis and rinitis are serous and remain serous also in the evolution of the inflammatory process. Another district that frequently developed in serous inflammation is represented by the nasal cavity at the beginning. Some virus produce serous inflammation for example adenovirus in dogs or in poultry can produce serous hepatitis. Macroscopically, adenovirus hepatitis not evident issues can be observed, only sometimes moderate increase of dimension of the liver due to exudation accumulation between hepatocytes. Histologically, you can observe sometimes areas of necrosis due to the pathogenetic mechanism of the virus, death of hepatocytes due to inflammation of the hepatocytes and the characteristic of adenovirus infection is the presence of an inclusion body in the hepatocytes. Adenovirus inclusion body is an accumulation of viral protein in nucleo and because of adenovirus replication into the nucleo of the cells. Another virus that can induce serous inflammation is represented by calicivirus (always in the liver). Calicivirus is a virus that produces serous hepatitis, but also systemic infection in rabbits particularly. It’s a severe infection of domestic and wild rabbits. We can see a liver that increases his dimension, a moderate serous hepatitis due to exudation.
We can see fibrinous tracheitis where there’s pseudomembranes. Fibrinous inflammations are frequently due to bacterial infection associated with suppurative inflammation , so we can see suppurative fibrinous inflammation in the lung. This is a suppurative fibrinous pneumonia. Almost all of alveolus fails by exudate which contains fibrin (filamentous structure) and leukocytes, in particular neutrophiles, are characterized by polylobulated nucleo and clear pink side cells. This is a microscopic picture of a dog with fibrinous suppurative peritonitis. It’s an inflammation in the peritoneal cavity due to bacterial secondary infection due to trauma. This is an enteritis in a cattle → severe hyperemia, dilation, multifocal, necrotizing and fibrinous-hemorrhagic inflammation.
This is the same case, but more severe with the necrotic areas of the intestinal mucosa. Here, we can see reactive hypertrophy of some peyers patches that represent the local intestinal and lymphoid tissue. Peyers patches also show destruction in the center, so necrosis and fibrinous exudate. This is adenovirus infection in bovine similarly to salmonella infections. 4) Suppurative (purulent) inflammation is generally due to bacterial infections. The typical sign of suppurative inflammation is called pus , a yellow exudate that contains a large amount of neutrophils (degranulated, dead), bacteria and macrophages. Suppurative inflammations are due to pyogenic bacterias like Staphylococcus aureus, Streptococcus pyogenes, Tueperella pyogenes, Escherichia coli, Pneumococcus etc, rarely some toxins. This is the classical aspect of a suppurative enteritis → pus. Histologically, we can see the structure → polylobulated neutrophils in the nucleo. Suppurative exudate can also be organized in abscess which is a localized collection of pus associated with colliquative necrosis surrounded by fibrous capsule. Abscess represents chronic suppurative inflammation. This is an abscess in the ventral tissue of the neck in a rabbit probably due to a traumatic agent.
REGENERATION OR REPAIR?
As I said before, an acute inflammation can progress and become chronic, can resolve or can repair. Regeneration or resolution or restitutio ad integrum consists in a proliferation of injury cells. Repair or scarring or healing is a replacement of damage cells by connective tissue. The possibility to have a repair or regeneration depends on some factors: ● cell types and regenerative ability ❖ labile cells (skin and gut) → excellent regeneration ❖ stable cells (liver and kidney) → little regeneration ❖ permanent cells (brain, heart) → no proliferative in postnatal life, so no regeneration → scarring ● remotion/persistence of the cause of damage is possible only when the agent is removed/destroyed. If the agent cause remain, it cause necrosis → repair ● type of damage ❖ minimal damage → resolution ❖ severe damage → necrosis → repair with a scar A damage of the skin may repair with a scar, generally in the derma, and regeneration of epidermis. Repair is characterized by substitution of damaged tissue with connective tissue , but there’s firstly a formation of intermediate tissue called granulation tissue. Granulation tissue is characterized by numerous blood vessels. The fundamental to bring nutrients to fibroblasts that move from the periphery of the damage and the need of nutrients to synthesize the cellular matrix and proteins. We can see the macroscopical and histological aspects of the granulation tissue and of the scar. The granulation tissue is regular in the surface and hyperemic because of the vessels to permite the increase of the blood to repair. It contains a lot of blood vessels, some mononuclear cells and a few fibroblasts that move from the periphery to the center portion. The scar is generally white and colorless because it contains a few blood vessels, so it is composed by a few fibrocytes and a lot of extracellular matrice.
CHRONIC INFLAMMATION
Chronic inflammation is a prolonged inflammation characterized by simultaneous presence of inflammation and repair. The most important players of this form of inflammation are mononuclear and infiltrate cells , in fact in abscess, we can find neutrophils and in parasite granuloma, we can find eosinophils. The destruction of tissue is increased in chronic inflammation in comparison to acute inflammation because inflammatory cells try to destroy pathogens and so release a great number of mediators to destroy pathogens and also the tissue. Generally, chronic inflammation is caused by: ● persistent pathogens, biological pathogens frequently with low pathogenicity and high resistance to phagocytosis like mycobacteria, fungi and parasites ● toxic agents for example silicon ● immunity factors ● foreign bodies (metals and vegetables) Granulomatous inflammation One of the most important chronic inflammation in veterinary medicine is represented by granulomatous inflammation. It’s a collection of mononuclear cells surrounded in chronic and advanced stages by a fibrous capsule composed of connective tissue (fibroblasts). Generally, granulomatous inflammation contains mononuclear cells like:
- lymphocytes
- macrophages
- epithelioid cells
- giant cells
- fibroblasts → they produce a fibrous capsule in advanced stage of chronic inflammation Granulomatous inflammation is caused by biological agents or foreign bodies. We can see a macroscopical aspect of a granuloma on the surface of the kidney.
Tuberculous granuloma We can see a tuberculosis granuloma in mediastinal lymph nodes → there are numerous circular structures in the mediastinal lymph nodes. This is the first period of the infection. We can see a tuberculosis granuloma in the lung, in the liver and in the intestine. Tuberculosis can affect all the organs because it’s an infection. Tuberculosis granuloma is composed of a necrotic coagulative center , represented in yellow in picture, that sometimes can present calcifications, so a deposit of calcium precipitates on the necrotic tissue. At the first stage formation, tuberculosis granuloma may contains a few number of neutrophils, the neutrophils are substituted by mononuclear cells, so lymphocytes, macrophages and cells derived from macrophages, epithelial cells and giant cells. In the advanced stage, the necrotic area is surrounded by fibrous capsules produced by fibroblasts that move from the periphery and try to limit/surround the issue.
We can see an histological picture of 2 granulomas in the lung. There is the classical fibrous capsule, different mononuclear cells like langhans giant cells and necrotic area. Pseudotuberculosis Another biological agent that causes chronic inflammation is Yersinia pseudotuberculosis. It produces more granulomas in the gut and surrounding areas in abdominal organs, in particular in rabbits, hares, ruminants, and cats. We can see numerous granulomas in the gut of a hare. We can see a small granuloma among lymphoid vessels of the mesentery in a sheep.
