44.2 Plasma Proteins

Question 1

• What is the histology of acute appendicitis?

Answer 1

• Swelling (tumor)
• Redness (rubor)
• Heat (calor)
• Pain (dolor)
• Loss of function (function laesa)

Question 2

What are the three general indicators of infection?

Answer 2

• Swelling (tumor)
• Redness (rubor)
• Heat (calor)

Question 3

What are the differences between acute and chronic inflammation?

Answer 3

Acute inflammation:

• Rapid onset (hours-days)
• Neutrophils are recruited
• Often a result of infection

Chronic inflammation:

• Long onset (weeks-years)
• Monocytes, macrophages and T-cells are recruited
• Possibly antigen driven -> in rheumatoid arthritis this is driven by self-antigens

Question 4

How can signals be amplified during inflammation?

Answer 4

• Platelets can be activated, and they produce many protein and peptide mediators
• Kinin cascades (poorly understood pathway related to inflammatory proteins in the blood), e.g. bradykinin
• Complement activation (enhances the antibody response)
• Histamine release (increases permeability of capillaries to allow entry of more WBCs)
• Cytokine secretion (signalling proteins, peptides and glycoproteins for the immune response)
• Prostaglandins (exacerbate inflammatory response through activation of receptors)

Question 5

How can plasma proteins be separated into their individual components?

Answer 5

Electrophoresis

• As blood is aqueous, the proteins within must be hydrophilic
• Smaller proteins travel further along the gel (also depends on polarity)
• Majority of plasma proteins are albumin

Question 6

What are the features and functions of albumin?

Answer 6

Features
- Around 50% of plasma proteins
- Reference range of 30-50g/L
- Soluble monomeric protein
- Negatively charged at pH 7.4 (normal blood pH)
- Plasma half-life of around 20 days
- Heavily glycosylated
Functions
- Maintains high osmotic pressure of the blood
- Transports hemin, bilirubin, free fatty acids, fat soluble hormones (non-specific lipid binding site) and thyroid hormones
- Binds to many drugs, affecting their pharmacokinetics (the less bound a drug is, the more likely it is to diffuse across or interact with a membrane)
-> e.g. Warfarin, NSAIDs, Diazapam and Digoxin

Question 7

What is the difference between plasma and serum proteins?

Answer 7

• Plasma is normal uncoagulated blood, whereas serum is removed blood with triggered platelets, causing coagulation and a different result on the electrophoresis
• Serum therefore contains a higher fibrin and granule content from the platelets

Question 8

• How can an electrophoresis indicate myeloma?

Answer 8

• Myeloma is a plasma cell cancer
• These produce antibodies
• Therefore a myeloma electrophoresis result would have a secondary high peak after that of albumin which is made up of antibodies)
• A load of a single antibody indicates a myeloma

Question 9

What are acute phase reactants?

Answer 9

• Host defence proteins made by hepatocytes
• This includes proteins involved in complement and coagulation cascades (e.g. C reactive protein, mannose binding lectin and clotting cascade factors such as fibrinogen and factor VIII)
• This can be triggered by inflammatory cytokines released as a part of the immune response which will interact with receptors in hepatocytes, such as IL-1, IL-6 and TNF-alpha

Question 10

What is the Pfieffer effect?

Answer 10

• This is where an animal (traditionally a guinea pig) is immunised against a particular bacteria (vivo cholerae)
• The guinea pig is then infected with the live bacteria, causing an immune response
• Serum from the immunised and infected guinea pig is injected into an uninfected and unimmunised guinea pig
• The guinea pig injected with the serum is then infected with the bacteria
  
  • > this guinea pig would survive/be able to fight off the infection, whereas the control experiment (unimmunised guinea pig infected with live bacteria, no serum) would just die

Question 11

Are complement and serum the same thing?

Answer 11

NO

• Serum is the clear component of blood that can be obtained after coagulation, consisting of electrolytes, proteins, antibodies, hormones and other exogenous substances
• Complement is the collection of plasma proteins that are involved with antibodies and the immune response
• Bordet demonstrated that they are two separate substances, as he found a heat labile substance (that COMPLEMENTED the action of antibodies) present in both immunised and non-immunised animals, whereas heat-resistant antibodies were only found in the serum of immunised animals
  
  • > both of these were shown to be involved in bacteriolysis/breakdown of the invading bacteria

Question 12

What are the key features of a complement system?

Answer 12

• Triggered enzyme cascade
• Rapid amplification of a small initial trigger stimulus
• Leads to 3 different types of anti-bacterial defence
  
  • > neutrophil recruitment
  • > opsonisation (coating of a protein in particles that will encourage the phagocytosis of that molecule by macrophages)
  • > membrane attack complex (MAC, formed by the host’s immune response on certain proteins found on the pathogen’s cell membrane)
• If there are defects in the complement cascade, this can cause an increased susceptibility to bacterial infection (e.g. C3 deficiency)
• Inappropriate complement activation is likely to be harmful (e.g. in lupus, where an overactive immune response results in the response attacking healthy tissue)
• This process is highly regulated and needs to be highly controlled in order to protect host membranes against attack

Question 13

How is the complement system organised and activated?

Answer 13

• 31 plasma proteins make up the system, all synthesised in the liver
• These will be rapidly recruited to sites of tissue injury
• Key component is C3b
  
  • > this is produced from a precursor via proteolysis/cleavage, this protein is C3
  • > this proteolysis is allowed through the generation of C3 splitting enzymes, aka convertases
• The activation of complement proteins leads to:
  
  • > terminal lytic events such as the MAC (membrane attack complex)
  • > recruitment of inflammatory cells
  • > opsonisation (where a pathogen is marked using antibodies for ingestion and destruction by phagocytes)
  • > killing of pathogens

Question 14

What are the different ways in which complement can be activated?

Answer 14

• Classical pathway, using antigen-antibody complexes
• MBP lectin pathway (lectins are proteins that bind to proteins MBP = mannan-binding protein, is an opsonin/involved in opsonisation)
• Alternative pathway (acts without the presence of an antibody)

Question 15

• Describe the classical pathway for complement activation.

Answer 15

• Links the antibody response to innate immunity/action of WBCs
• C1q binds to antigen-antibody complexes
• 6x molecules of C1q associated with C1r and C1s
• Binding of C1q causes C1r to cleave C1s into an active form
• C1s cleaves C4 and C2 to generate C4b and C2b
• C4b2b is an active C3 convertase, which is the key member of the complement