NMSK - cell signalling

Week 1 -

What are 5 reasons cell signalling is important and why

1. Movement (volvox is the most primitive multicellular organism, movement is achieved by cilia beating on every cell, arranged in a sphere therefore can be organised. The movements are brought about by ion movements through cytoplasmic bridges)

2. Metabolism (differentiated cells have distinct metabolic processes that are communicated vie chemical signals)

3. Growth (cells bathed in nutrient rich medium without growth signal factors would grow uncontrollably and result in things such as cancer).

4. Development (during development, ectoderm overlying the notochord is induced to become thickened, forming neuroectoderm)

5. Immune response (involved in the activation and recruitment of neutrophils for cytokine production which stimulates other cells)

How can cells communicate b/w each other

Cytoplasmic bridges that allow signaling molecules to pass b/w cells w/o being secreted into extracellular fluid - GAP JUNCTIONS

Outline the function/role of gap junctions

• allow ion movement

• allow metabolite and intracellular signalling molecules (e.g. cyclic AMP) movement

• essential in embryonic development

• only b/w adjacent cells

• slow transmission across an organ

• potential transmission of deleterious factors from one cell to another.

outline synaptic transmission

• communication between neurones involving a chemical messenger across a short synaptic cleft.

• no dilution in general circulation

• reactivated very quickly

Disadvantages? - specificity due to synaptic interactions

hardwiring is expensive - metabolic maintenance of the neurological system

possibly vulnerable (neurones take a long time to heal)

What is receptor cell mediated signalling, label the image correctly

• local/long distance communication

1 - autocrine

2- paracrine

3- endocrine

Give an outline of the 3 types of receptor mediated signalling

1. Autocrine - self signalling, target the same cell they were made at

2. paracrine - signalling molecules manufactured by the original cell target cells very close by

3. endocrine - utilise the circulatory system to target cells far away from the original manufacturing cell

How is specificity maintained?

Sometimes:

• cell to cell contact is required

• pr receptors may be needed instead

only the target cell will have an active site that matches the signalling molecules shape

Outline cell membrane structure

• a mosaic of different proteins imbedded in a fluid matrix of the lipid bilayer

• held together primarily by hydrophobic interactions

• most lipids and some proteins can drift about laterally

• phospholipids rarely move

• proteins and large molecules move sloewr and some in a highly directed manner

• fluidity is temperature dependent

  flexible

How do we control membrane composition and why

• fluid environments therefore proteins integrated in them can move around

• for signalling events it’s essential that the number of interacting proteins are close in proximity to each other

How do we do this? LIPID RAFTS

• a section of membrane (microdomain) that are more stabilised and rigid structures THROUGH CHOLESTEROL and SPHINGOLIPIDS.

• they float as a ‘raft/island’ within the membrane

• proteins integrated will stay in close proximity to each other, which allows a number of processes including interactions for signalling across the membrane.

External/lumen side = receptor concentrated

cytosolic side = intracellular signalling messengers are concentrated.

Fill in the gaps

endocrine, receptor dependent, specific, active site, phospholipid, hydrophobic

What are cytokines

Soluble proteins/glycoproteins produced by cells

important signalling molecules, especially in the context of inflammation and innate immunity.

examples include Chemokines (CXCL8, a specific group)

What do cytokines do?

• mediate and regulate immunity (innate and adaptive), haematopoesis and embryogenesis

• signals setting out the local cellular environment

• brief and self limiting if the stimulus is removed.

What cells can produce cytokines?

All cells

What is pleiotropy and explain it

Pleiotropy is an effect cytokines can have on a cell.

Binds to multiple cells and each cell will have a different reaction and outcome

What is redundancy

When 2 or more cytokines have the same/similar effect on a cell

What is synergy

The combined effect of cytokines which may be greater/additive compared to each individual cytokine alone

What is antagonism

One cytokine may inhibit the activity of another

What is cascade activation

one cytokine may induce a cascade of cytokine expression involving multiple cells

How can we describe how cytokines work

a network

• rarely act alone

• responses often involve numerous cell types and a range of cytokines

How to cytokines regulate inflammation

They’re either pro/anti-inflammatory

Give example of both pro and anti-inflammatory cytokines

Pro = TNF(alpha symbol), IL-1, IL6, CXC-8/IL-8

Anti-inflammatory - IL-4 and IL-10

what is an inflammatory response

• an innate immune reaction that ensures immune cells and other substances are brought to the affected area

why do we have inflammation responses

• foreign organisms may be destroyed or inactive

• injured tissue/cell remnants may be removed

• tissue pair is initiated (need to consider during surgery)

what causes inflammation

causes - infection, heat, chemical substances/burns, mechanical inury, other

disorders - asthma, allergies/hypersensitivites, obesity, osteoarthritis, chronic prostitis, autoimmune diseases, diabetes, inflammatory bowel disease

what is acute inflammation

• normal response, what you’d expect to deal with

• repair or damage of removal of infection removes the stimulus i.e. you’ve had a thorn/break in skin, there’s an accumulation in the area of inflam, then it returns to normal state.

• examples - microbial infections, hypersensitivity, physical (burn/ UV light), necrosis)

what is chronic inflammation

progression of acute inflammation if healing process doesn’t occur because of foreign body or continuing infection

may occur when no obvious foreign body is present

means you have weeks, months maybe years of an inflammatory process

examples - persistent infection

persistent presence of foreign bodies

immune mediated disease

what are the effects of inflammation

• rubor (redness),

• calor - heat

• tumor - swelling

• dolor - pain

• lack of function

Outline how acute inflammation work on a mucosal surface

1. At the site of infection cytokines are released/signalling molecules that stimulate neutrophils

2. Neutrophils release cytokines which stimulates other resident cells

3. Mast cells release histamines and other vasoactive substances that increase vascular permeabitlity

4. acute phase reactants such as chemokines attract neutrophils and monocytes. These migrate out of the blood vessel to the site of infection

5. The infection is dealt with

6. The inflammation response is ‘turned off’.

How is inflammation initiated

• At the source of infection epithelial cells and resident macrophages release chemokines and cytokines (e.g. CXCL8/IL8)

• These chemicals attract other cells e.g. First migratory WBC to the site will be neutrophils, then blood derived macrophages.

• This leads to a greater response

Give 6 examples of pro-inflammatory mediators, what they’re released by and what they do

• released by stimulated epithelial cells

  1. IL1(beta) - activates vascular endothelium, local tissue destruction, increases access for the effector cells and stimulates IL-6 production

  2. TNF (alpha) - activates vascular endothelium, increases IgG entry, complement and fluid drainage to lymph

  3. IL6 - lymphocyte activation, increased antibody production

  • These all lead to infiltration of leukocytes

    4. CXCL-8 - attracts neutrophils, basophils and T-cells to the site of infection (leads to attraction of leukocytes)

    5. Prostaglandins and Leukotrienes - stimulation of vascular smooth muscle cells and neurones (leads to vasodilation and pain)

    6. IL12 - activates NK cells, induces differentiation of CD4 T cells into T(subscript)H 1 cells (leads to activation of adaptive immunity)

What often causes more damage during an inflammatory response?

• The body’s own response

• Some cytokines/chemokines cause damage to the body, e.g. IL1-beta so that the necessary cells (leukocytes) can infiltrate the area to stop infection.

What are some systemic effects of pro-inflammatory mediators

• fever (raised temperature will help kill bacteria, as they cannot usually survive the high temperature)

• Mobilisation of metabolites

• Induction of acute phase proteins

What do phagocytes do in the inflammatory response?

Outline the inflammatory cascade

• inflammatory cell infiltrate produces more cytokines and chemokines

• more resident cells become activated and more cells extravasate (including lymphocytes)

• amplification of immune response leading to clearance of antigen.

Outline the role of mast cells and how we can recognise them

Recognise - characteristic secretory granules (look grainy)

• present in the Interstitium (spaces b/w cells/tissues)

• can be activated by the initial inflammatory response

On activation:

• rapidly release their granules and inflammatory mediators into the interstitium

• preformed mediators (from granules) - histamine (2-5pg/cell), proteoglycans (heparin, anticoaglulant), serine proteases (digest specific protein bonds)

• newly formed lipid mediators (eicosanoids), prostaglandin D2 (can constrict airways and dilate blood vessels), leukotriene C4

• cytokine release

What are the effects and what does the release of histamines lead to

effects:

• dilation of blood vessels

• permeability of vessels increases

• activation of the endothelium (change of properties)

Leads to:

• warmth

• redness

• local oedema

• attraction of other inflammatory cells to the site of release

what are some clinical signs of histamine release

1. irritation of nerve endings leading to itching/pain

2. ‘flare and wheal’ reaction - bumps and redness immediately following a mosquito bits/allergy testing (can happen after seconds)

what are the differences between mast cells and basophils

• once mast cells have released histamine and other chemicals, these cause other immune system cells called basophils to prolong the reaction, damaging tissue.

Mast cells - tissue cells, release histamine, major role in asthma

Basophils - blood, release histamine, major role in anaphylactic shock

What is tethering and rolling?

• blood vessel endothelium, local to the area of infection will express new receptors called SELECTINS (integrin receptors)

• These cause certain leucocytes in the vessels to express INTEGRINS which can bind to the receptors

• this binding slows down the leukocytes near to the area of infected tissue, this leads to their immobilisation

What happens after ‘tethering and rolling’

DIAPEDESIS

• immobilised leukocytes reorganise their cytoskeletons

• changes the cell shape and they ‘spread out’ over the endothelium

• leukocytes pass between the gaps in the endothelial cells.

What are acute phase reactants/proteins and give 3 examples

• plasma proteins

• produced in the liver in response to cytokines secreted during inflammation - up to 100fold increase in their concentration

• markers for systemic inflammatory response - non-specific

examples

• C-reactive protein (IL6 response)

• fibrinogen (IL6 response)

• Serum amyloid A protein (IL-1 and/or TNF alpha response)

How do we resolve inflammation and what is it called?

• returning to a stead state

• Reduced presence of antigen reduces cytokine/chemokine production which leads to anti-inflammatory cytokines and inhibitors inhibiting the production and effect of pro-inflammatory cytokines, then the healing stage and return to homeostasis.

what are anti-inflammatory cytokines and give 2 examples

• help control the pro-inflammatory response

• act in concert with specific cytokine inhibitors and soluble cytokine receptors to regulate the immune response

• physiological role in inflammation

• pathologic role in systemic inflammatory states

examples are IL-4 and IL-10

What is the difference between acute and chronic inflammation?

Acute - there’s a resolution following the immune response and homeostasis is reached.

Chronic - there’s no resolution and the immune response and inflammation are excessive

What happens if the inflammation is not ‘switched off’?

• granulomas can form as a result of chronic inflammation

• accumulation of immune cells

What are granulomas

• aggregates of chronically stimulated inflammatory cells

• millimetre size range in tissue (can be detrimental in tissues such as lung)

• confluent, forming larger areas

essential components are:

• collections of modified macrophages called epithelioid cells, which when merged together (more than one epithelioid cell) forms a Giant cell/Langhans cell

• a surrounding zone of lymphocytes.

Why can granulomas be dangerous in immunocompromised individuals?

For pregnant/old/very young/immunocompromised individuals, if the granuloma ruptures, this can result in an active infection if the pathogen has not been destroyed.

How to Granulomas form?

• macrophages act as scavengers engulfing small particles.

• The macrophages have persistent stimulation which summons more macrophages.

• Prolonged stimulation results to macrohpages fusing which forms the ‘giant/langhans cells’

What main leukocyte would you expect to see in the stifle joint fluid of an animal with septic arthritis

mostly neutrophils, small amount of monocytes and if the infection is severe maybe even the pathogen itself.

Summarise the role of inflammation

• necessary immune process

• increases the efficiency of effector immune cell contact with foreign bodies

• inflammation may be acute/chronic

• cytokines place an essential role in its development as well as in dissolving inflammation to allow healing

• chronic inflammation and disease may occur if the acute inflam response isn’t controlled

• ganulomas form when the immune system attempts to wall off substances it perceives as foreign but is unable to eliminate e.g. infectious organisms or foreign object