IMMUNOLOGY

Bios 328a textbook-based study of immunologySpring 2003

http://www.lehigh.edu/~sk08/Courses/Bios328/mainpage.htm

• “A fascinating and personal portrait of the immune system. In Callahan’s picture, it’s the immune system, not our brains that defines our humanity.”– Joe Palca, NPR Science Correspondent

• “Sophisticated yet easy to understand… Callahan takes his readers on a poetic and exploratory voyage.”– Rocky Mountain News

• “Drawing poignantly on the stories of his own life, Callahan contends that experiences as complex as love and madness are intricately bound up with our immunological makeup.”– Discovery

• Each of the dozen essays in this far-ranging collection could be expanded into a book… ‘the Flame Within’ is …a detective story about the best-documented instance of human spontaneous combustion which occurred in Florida in 1951…”– Booklist

Today…

• Student course evaluation…

• Complete group 7’s presentation…

• Complete presentation on complement…

• Present statement about monoclonal Ab’s…

• Attend to mechanical concerns…• Return of take home quizzes…• Anticipating the nature of the final comprehensive

exam

CANCER

Cancer Vaccines

• Genetic

• Biochemical

HPV

Human Papilloma Virus

• E6

• E7

From Normal to Abnormal:

For more info

• HPV

• Cancer Vaccines

This Day Has Been Brought to

you By the Letter…

CC is for Cancer!

                       

COMPLEMENT

The overview….

• Complement has three functions:

– Opsonin

– Chemoattractant

– Membrane Attack Complex (MAC)

• Complement functions in two (three?) systems:

– Alternative

– Classical

– Lectin-based

The CLASSICAL pathwayStimulated by antibodies:

specifically: IgM and IgG (subclasses 1, 2, 3)

Start with C1q a HUGE protein (410,000 daltons!)

Composed of 18 peptides. Peptides can associate to

form trimers; six sets of trimers make C1q.

C1q has helical “stalks” and globular “heads.”

(N. B. the heads are the carboxy end and the stalks are the amino ends)

The CLASSICAL pathway

Also associated with C1 are C1r and C1s which associate to make dimeric pairs (C1r2s2); the dimeric pair joins C1q to form C1qr2s2.

The CLASSICAL pathway

• C1qr2s2 binds to TWO immunoglobulins.

– The complement binding sites of circulating IgM are too far apart to bind complement;

– only when IgM is bound does it fold so that C1qr2s2 can “see” nearby complement binding domains.

– IgG concentrations must be high in the vicinity of antigens for threshold levels of complement binding domains to be present.

The CLASSICAL pathway

• When C1qr2s2 is bound to requisite number of immunoglobulins, C1r “autocatalytically” converts to C1[r].

• C1[r], in turn, converts C1s to C1[s].

• C1[s] cleaves C2 and C4.

• C4 is cleaved to C4a and C4b; C4b associates with its “target” which is C2.

• C2 is cleaved by C1[s] making C[4b2a] which is a C3 convertase! (Note that 2a is bigger than 2b, this nomenclature being the one exception to the convention that “a” is smaller than “b.”)

• As with the other C3 convertase, C3b can join C[4b2a] to make

C[4b2a]3b which is also a C5 convertase.

The CLASSICAL pathway

The CLASSICAL pathway

The CLASSICAL pathway

The complement pathways…

The LECTIN pathway

• Lectins are proteins which bind to carbohydrates.

• Many bacteria have many mannose residues on their surface. The lectin-based complement system begins with a “mannose-binding protein” (MBP).

• MBP reacts, in turn, with a MBP-associated serine protease (MASP).

• MASP functions, in effect, like activated C1q[r2s2], that is a C3 convertase.

The mostamazingcircumstance:

• Erythrocytes (!) deliver the complex of antigen –antibody – complement to the liver and spleen for consumption by phagocytes.

Monoclonal Ab’s

Contrast with the normal circumstance…

• The normal response to an immunogen is polyclonal Ab’s

• The immunogen most commonly has multiple epitopes

• The multiple epitopes select multiple B-cell lineages

• Multiple clones mature to produce Ab’s for the multiple epitopes

Monoclonals are just what they say they are:

• Remember: a single B-cell makes a single type of antibody– or, more precisely, a single idiotype

• The B-cell is made immortal– The clone, if stable, continues to secrete the

single type of Ab

The scheme…• “HGPRT+” =‘s

hypoxanthine-guanine phosphoribosyl transferase

• The enzyme is used in the “salvage pathway” for DNA synthesis

• “HAT” =‘s hypoxanthine -- aminopterin -- thymidine medium

• aminopterin inhibits de novo DNA synthesis

• thymidine is needed for pyrimidine synthesis in the salvage pathway

• hypoxanthine for purines...