List the seven major functions of the complement cascade. (7 marks) A gram-negat

Question

List the seven major functions of the complement cascade. (7 marks)

A gram-negative bacterium is present in the blood of a host. List and briefly describe the three ways that the alternative pathway of complement could be activated. (6 marks)

An individual is deficient in the complement component C3. Describe the consequences of this deficiency for each of the following:

activation of the membrane-attack complex (MAC)

phagocytosis of pathogens

clearance of immune complexes

presentation of antigenic peptides from infectious bacteria (4 marks)

Some pathogens are capable of evading the complement cascade. Select one pathogen that demonstrates resistance to attack by the complement cascade and indicate the mechanism by which this is achieved. Finally, describe the effect this evasion would have on the infected individual. (5 marks)

Fill in the following diagram of an antibody with the following terms: heavy chain, light chain, antigen binding site, hinge region, variable region, and constant region. Be sure to indicate all regions. (3 marks)

List the five classes of antibody heavy chains and provide one function for each. You will need to consult Chapters 3 and 13 of the text. (10 marks)

List and describe briefly the means of antibody diversity in naïve B cells. (10 marks)

What is allelic exclusion and why is it important? (5 marks)

What genes are rearranged to produce a functional T-cell receptor? Make sure you indicate the genes for each of the and chains. (5 marks)

What is the function of the RAG1/2 enzymes? What are the genes that encode these enzymes? (4 marks)

What is a haplotype? Genes within the MHC locus exhibit a codominant form of expression, what does this mean? In terms of combatting infection do you think it would be advantageous to produce offspring from two parents that were more similar or dissimilar in their MHC alleles? (5 marks)

Draw the structure of the MHC Class I and MHC Class II molecules. What type of T cell does each of these molecules associate with? (10 marks)

Explain the concept of self-restriction in terms of major histocompatibility complexes (MHC) and T cells. Outline an experiment that demonstrates this concept. (5 marks)

Draw both the exogenous and endogenous pathways, and indicate the mechanism of antigen processing and assembly with MHC. (16 marks)

What is TAP and what is its function? What happens to individuals who have a deficiency in TAP? What is this condition called? What are some of its associated symptoms? (5 marks)

Explanation / Answer

1.Functions of complement cascade:

Virus neutralisation-Complement helps eliminate virions by inducing them to aggregate,and by coating the capsid.

It enhances the immunity system.C3 is required for optimal expansion of CD8 T cells during systemic viral infections.

Lysis-The first complement cascade function discovered,cell lysis begins with pores forming in the cell membrane,and ends with fluid rushing into and bursting the cell.This complement function is not effective against organisms with cell walls,including gram-positive microbes and fungi.

Opsonization (preparation of cells for phagocytosis) is performed by macrophages and polymorphonuclear leukocytes.A cleave product called C3b is formed by binding of macrophage and PMN F(c) receptors to antibodies.C3b is the primary opsonin, coating antigens to form an antigen-C3b complex.This complex then stimulates phagocytosis by binding phagocytices' complement receptors.

Inflammation-Anaphylatoxins C3a,C4a and C5a are small peptides produced during the complement cascade, and induce inflammation.Anaphylatoxins bind mast-cell and basophil receptors,induce degranulation to cause smooth muscle contraction and vascular permeability. Also,anaphylatoxins amplify the inflammatory response by inducing synthesis of pro-inflammatory cytokines. 5a is the most potent anaphylatoxin.Along with C3a and C5b67,C5a also is a chemoattractant an activator of white blood cells it induces monocytes and neutrophils to bind capillaries vascular endothelium,extravasate out of the capillaries and migrate to tissue where complement has been activated.

Immune clearance-C3b facilitates binding of immune complexes to CR1 on red blood cells.As these red blood cells pass through the spleen and liver, the immune complexes are removed and phagocytosed.In addition,complement helps make immune complexes more soluble which leads to immune clearnace.

chemotaxis-attracting of cells of immune system

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