AB2 Learning Objectives

Describe sources of cell injury with examples

External: UV and x-rays, temp extremes, chemicals and pollution, work and lifestyle, pathogens and infectious agents
Internal: aerobic respiration, proteolytic or oxidative enzymes (lysosomes), immune cells (neutrophils), reactive intermediates generated by metabolic pathways (endogenous like xanthine oxidase or exogenous like chemotherapies)

Consequences of macromolecular damage to macromolecule and cell function

Genetic modifications, protein aggregation, cell death, and structural and functional changes in the cell membrane

Autophagy process

Autophagy is an ancient defense mechanism against invading organisms. Microorganisms are engulfed and packaged into vacuoles (autophagosome), fused with a lysozyme, and destroyed by proteolytic cleavage and the autophagy pathway.

Explain how infection with pathogens can cause cell injury and damage due to the presence of pathogens

Bacterial Infection: bacteria compete with host for extracellular nutrients, bacterial metabolism impacts extracellular pH and compromises homeostasis, accumulation of waste products

Viral: Infection causes significant ER stress due to increased demand on protein synthesis

Explain how infection with pathogens can cause cell injury and damage from the immune systems attempt to resolve the infection

Antiviral defenses (interferon) restrict ER protein synthesis and shut down viral replication, which leads to accumulation of unfolded proteins and ER stress, activating the Unfolded protein response

Examples of pathogen strategies to overcome these protective pathways

• prevent neutrophil respiratory burst by inhibiting NADPH oxidase activation

• DNA damage repair pathways to detect and repair ROS damage bacterial DNA

• Modulate ER function and autophagy

• Dampen interferon activation of ER unfolded protein pathway

• Bacterial chaperones to assist protein refolding

• Have antioxidants and antioxidant enzymes to detoxify ROS

Reactive oxygen/nitrogen species

Unstable oxygen derivatives usually contain an unpaired electron. Important role in cell signaling, metabolism, gene expression, and host defense mechanisms. Highly reactive; steals electrons from other molecules.

Free radical

an unstable atom or molecule with at least one unpaired electron in its outer shell

Electrophile

an electron-deficient chemical species that accepts a pair of electrons from an electron-rich nucleophile to form a covalent bond

Oxidative damage

Radical lipid formation after attack from ROS and reactive molecules. Causes chain reaction of damage called lipid peroxidation where reactive lipids attack neighboring lipids to steal electrons

Lipid peroxidation

Chain reaction of damage where reactive lipids attack neighboring lipids to steal electrons

Protein adduct

complex formed when a reactive chemical species covalently binds to a protein

Protein aggregate

a collection of misfolded or unfolded proteins that stick together inside or outside the cell

Antioxidant

any substance that significantly delays or prevents the oxidation of crucial cellular molecules like DNA, proteins, and lipids by neutralizing harmful free radicals.

Chaperone (cell bio)

a group of proteins that help other proteins fold correctly, prevent them from clumping together, and assist with their movement or breakdown inside the cell

Heat shock protein

a family of stress-induced molecular chaperones found in all living cells that help maintain protein folding and prevent cellular damage

Proteasome

a large protein complex inside cells that breaks down unneeded, damaged, or misfolded proteins into small peptide pieces through proteolysis

Lysosome

a membrane-bound cell organelle that holds digestive enzymes to break down waste

Unfolded protein response

a cellular stress-signaling pathway activated by eukaryotic cells to manage the accumulation of unfolded or misfolded proteins in the lumen of the endoplasmic reticulum

Respiratory burst

a rapid, short-term increase in oxygen consumption by cells that produces large amounts of reactive oxygen species to kill engulfed pathogens

Types of cell death

Necrosis: hard and fast death caused by acute injury or excessive stress

Apoptosis: Programmed and controlled cell death that is important for many physiological processes

Compare and contrast the cellular phenotype of reversible vs irreversible cell damage

Contrast necrosis vs apoptosis

Importance of caspase cascades in apoptotic cell death

Start the apoptotic process using very specific enzymes then catalyse the widespread cleavage of proteins to kill the cell. Caspases are kept as inactive precursors to prevent unwated activation of cascade.

Similarities between intrinsic and extrinsic apoptotic pathways

Both cleave thousands of proteins and cell adhesions, shrink and bled, and irreversibly fragment DNA, nuclear envelope, and cytoskeleton. Both start after cytochrome C is released by the mitochondria which triggers formation of apoptosome and the start of apoptosis.

Differences between intrinsic and extrinsic apoptotic pathways

Extrinsic also has the death receptor that triggers the disc complex to gather enzymes together, releasing caspase 8 and beginning apoptosis

Role of immune system in clear up of apoptotic and necrotic cell death

Apoptopic cells attract phagocytes using soluble mediators and signals they are ready to be eaten using PS receptors.

Necrotic cells’ debris contains DAMPS which are recognized by the immune system, allowing for macrophages to locate and phagocytose the DAMPS and cell debris

Types and severity of damage that will elicit apoptotic cell death

Mainly preventative, removing potentially harmful cells. EX: eliminating auto-reactive B and T cells, T-cells with strong reaction to self antigens, interdigital remodeling

Types and severity of damage that will elicit necrotic cell death

Acute injury or excessive stress such as heat, irradiation, loss of oxygen, infection, etc. For extensively injured cells that are damaged beyond repair

Bleb

a spherical, blister-like bulge or protrusion of the plasma membrane caused by the localized decoupling of the cytoskeleton from the cell membrane

Karyohexis

fragmented nuclear DNA

Pyknosis

irregular and irreversible condensation of nuclear DNA

DAMPS

Damage-associated molecular patterns

Caspase

contain a cysteine at their active site and cleave proteins after aspartate residues

Initiator caspase

start the apoptotic process

Executioner caspase

catalyse the widespread cleavage of proteins to kill the cell

Cytochrome C

a small heme-containing protein found in the mitochondrial intermembrane space that shuttles electrons during cellular respiration and triggers cell death when released into the cytosol

Apoptosome

a large, wheel-shaped protein complex that forms inside a cell during the intrinsic pathway of programmed cell death

Bcl-2

Anti-apoptotic protein that prevents inappropriate release of cytochrome C from mitochondria

Bax and Bak

Pro-apoptotic proteins that punch pores in the mitochondrial membrane to the let cytochrome C escape

Phosphatidylserine

a major negatively charged phospholipid found mainly in the inner cytoplasmic leaflet of eukaryotic cell membranes

Neoplasia

The process of abnormal growth of a tissue into a mass

Tumour def

An abnormal growth of tissue into a mass. Can be benign or malignant

Cancer def

a malignant tumour which has the capacity for both local invasion and distant spread by the process of metastasis

Oncology def

a branch of medicine that specializes in the diagnosis and treatment of cancer

Carcinogens def

agents that promote cancer

Metastasis def

spread of cancer cells from the primary tumour to another part of the body

Oncogene def

mutated version of proto-oncogene which causes cells to grow and divide uncontrollably

Tumour suppressor gene

aka anti-oncogenes. a normal gene that encodes a protein to slow down cell division, repair DNA mistakes, or tell cells when to die through apoptosis

Features which distinguish between benign and malignant tumours

Describe what causes cancer

Cells have undergone genetic changes that allow them to be unresponsive to growth controls and expand beyond anatomical boundaries. Inherited mutations, multiple mutations, and acquired somatic mutations can all cause cancer.

Explain multistage progression and evolution of cancer

Initiation and promotion go very slowly while progression is a rapid onset that is hard to stop

Direct clinical consequences of neoplasia

• compression of tissues and blood vessels

• blockage of tubular structures

• organ rupture

• organ failure

• haemorrhage

• tumour emboli

Indirect clinical consequences of neoplasia

paraneoplastic syndromes

Classes of parasites

Protozoans, helminths, arthropods

Classes of helminths

Nematodes (roundworms), trematodes (flatworms), cestodes (tapeworms)

Classes of arthropods

insects, ticks, mites

Reproductive mechanisms in parasites

• High production → low survival

• Low production → high survival

Causes of overdispersed distribution of parasites

• variability in host susceptibility/immune competence

• most parasitic diseases are endemic so host populations consist of acquired immunity, poor immunity, and no immunity

• environmental factors

Harms associated with parasites

• pruritic stress (itching)

• biting nuisance

• acute inflammatory response

• physical damage of host tissues and organs

• competition for resources

• transmission of other pathogens

Describe the function of lymph

Cardiovascular: fluid balance and homeostasis

Immune: component of the surveillance system that defends the body

Describe the formation of lymph

Lymph forms when capillary hydrostatic pressure forces fluid out into the tissues, and incomplete reabsorption by osmotic pressure leaves an excess that enters lymphatic capillaries

Describe the structure of lymphatic capillaries

Blind ending tubes made up of loosely overlapping endothelial cells surrounded by a fibrous collagen layer with simple flaps to prevent back flow. Resemble blood capillaries

Describe the manner in which lymph enters the capillaries from the tissues

Pressure in interstitial fluid causes fluid to open mini valves (intercellular clefts formed by loosely overlapping endothelial cells) and enter the lymphatic capillaries . Pressure inside capillaries prevents escape of lymph

Describe the anatomy of collecting lymph vessels

specialized three-layered tubular channels that actively propel lymph from initial capillaries toward lymphatic trunks and ducts

Describe the anatomy of larger lymph vessels

a three-layered wall structure similar to veins, complete with internal one-way valves that give them a beaded appearance

Explain the factors promoting lymph flow

The major force of movement is the muscle pump, the contraction of muscles through which the lymphatic vessels pass force the lymph fluid downstream. Abdominal and thoracic pressures associated with breathing also help. Larger lymphatic vessels have smooth muscles that produce small pulses of pressure. Valve flaps prevent backflow.

Identify the function of the thymus in the lymphatic system

production and primary maturation of t cells

Identify the function of bone marrow in the lymphatic system

Production and primary maturation of B cells. Production of T-cells

Identify the function of the spleen in the lymphatic system

Screens blood

Identify the function of peyer’s patches in the lymphatic system

critical immune surveillance hubs in the small intestine (primarily the ileum) to monitor gut microbes and initiate mucosal immune response

Main lymph groups in the head

The retropharyngeal group

Main lymph groups in the thorax

The mediastinal group

Main lymph groups in the abdomen

The mesenteric group

Main lymph groups in the limbs

The iliac group drains the hind limb while the axillary group drains the forelimb.

Describe innate immunity

Non-specific, rapid immune response with a broad recognition that is found in all animals. It depends on physical barriers, killing/cytokines, and phagocytes due to its lack of memory

Describe adaptive immunity

A specific, slow immune response with an immunological memory that is found in vertebrates. Depends on lymphocytes, antibodies, killing cytokines, and TCR/BCR.

Describe the differences between cell mediated and humoral immunity

Humoral: An invading pathogen in the blood or lymph has foreign antigens on its surface. This activates B cells which then produce antibodies against the antigen. Cell-mediated: One of the body’s own cells becomes changed in some way. For example a cell is Infected by a virus or a cell becomes cancerous. This triggers T lymphocytes which kill the infected cell.

Explain how anatomical location of pathogen influences immune responses

3 major sites: in tissues, blood, or mucosal sites. Lymph nodes respond to pathogens in tissues, spleen filters blood, and MALT combats infections that enter through mucosal surfaces.

Explain how cellular location of pathogen influences immune responses

Does the pathogen live inside or outside the cells? Intracellular pathogens are controlled by cell-mediated immunity, with humoral immunity playing a minor role. Extracellular pathogens use complements which bind to the surface and lead to enhanced phagocytosis or direct lysis.

Explain how the outcome required after infection influences immune responses

Can outcome be induced by vaccines or immune stimulation to avoid future infections and aid adaptive immunity? Focus on how to avoid rather than how to fix problem.

Describe physical mechanisms in innate protection

Includes skin, ciliated mucous membranes, commensals, etc. First line of defense against pathogens that hopefully prevents them from ever getting inside.

Describe humoral mechanisms in innate protection

Includes enzymes (breaks down cell walls), iron chelators (sequesters iron away), antimicrobial peptides (Punches holes in bacteria), and complements (cascade to cause death).

Describe cellular mechanisms in innate protection

Consists of phagocytosis, specific cells, and granules. Cells that kill pathogens.

Identify cells of the innate immune system and their major roles

Neutrophils: Phagocytosis and killing

Eosinophils: Release cytotoxic molecules for direct killing

Basophils: Respond to allergic inflammation

Monocytes: Sense danger through pattern recognition receptors, antigen presentation, phagocytosis, and intracellular destruction of pathogens

Natural killer cells: Kill infected cells and release cytokines to influence adaptive response

Mast cells: Release a wide variety of inflammatory mediators

Explain what innate receptors recognize and their role in the recognition of danger

PRRs recognize PAMPs, which trigger intracellular signaling cascades that lead to altered gene expression

Describe the consequences of danger recognition by cells of the innate immune system

PRRs recognize PAMPs, which trigger intracellular signaling cascades that lead to altered gene expression and the downstream function of the specific cell that recognized the PAMP

Inflammation Definition

A protective response intended to eliminate the initial cause of cell injury as well as the necrotic cells and tissues resulting from the original insult

Name stimuli for inflammatory reactions

• Physical: cuts, burns, etc

• Chemical: acids, alkalis, etc.

• Microbial: bacterial, parasites, etc.

• Immunological: normal immune responses to infectious agents, hypersensitivity reactions, etc.

Describe cardinal signs of inflammation

• Heat

• Redness

• Swelling

• Pain

• Loss of function

Explain changes in vascular responses during inflammation

• Hyperaemia: inc blood flow into tissue

• Sludging of erythrocytes

• Stasis (thrombosis)

• Margination of leukocytes

• Increased vascular permeability

Effects of mediators on the organism

Vasodilation, increased vascular permeability, pain

Mediators inducing vasodilation in acute inflammation

histamine, serotonin, prostaglandins, nitric oxide

Mediators inducing increased vascular permeability in acute inflammation

histamine, serotonin, Bradykinin, Leukotrienes, Cs

Mediators inducing pain in acute inflammation

Prostaglandins and bradykinin

Biological functions of the complement cascade

A series of serum components found in all animals that serves to implement a large response from a small signal leading to the removal of the pathogen.

Describe the alternative complement pathway of activation

Does not require antibodies or recognition of PAMPS and is innate. C3 spontaneously hydrolyzes into C3b which binds to pathogens and MAC occurs. Host cells contain sialic acid, which activates factors H and I which can deactivate C3b, keeping the host cell safe.

What is MAC

Membrane attack complex is the end product of the 3 complement pathways. Complex of components C5b, C6, C7, C8, and C9 that forms a pore in the microbial membrane to kill pathogens

Describe the classical pathway of activation

Triggered by antibody/antigen complex formed in the adaptive humoral response, so slow. The complex binds to C1, activating the protease activity of C1r and cleaving C4 and C2 to make C3 convertase. C3 is hydrolyzed, making C3b which cleaves C5 to make C5b which attaches to the microbe surface and leads downstream to MAC and other outcomes.

Describe the MB-Lectin complement pathway of activation

Lectin binds to pathogen surfaces and is triggered by bacteria with sugar rich cell walls