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FIRST HALF OF TODAY’S CLASS: THE IMMUNOGLOBULINS PowerPoint PPT Presentation


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FIRST HALF OF TODAY’S CLASS: THE IMMUNOGLOBULINS. A quick overview of the five immnoglobulin “ classes ”. IgG ( ( globulin ): the prototypic immunoglobulin. All three general functions (Ag binding, complement activation, stimulation of phagocytosis) occur.

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FIRST HALF OF TODAY’S CLASS: THE IMMUNOGLOBULINS

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First half of today s class the immunoglobulins l.jpg

FIRST HALF OF TODAY’S CLASS: THE IMMUNOGLOBULINS


A quick overview of the five immnoglobulin classes l.jpg

A quick overview of the five immnoglobulin “classes”

  • IgG (( globulin): the prototypic immunoglobulin.

    All three general functions (Ag binding, complement activation, stimulation of phagocytosis) occur.

  • IgM (macroglobulin): often the first

  • IgA: the secretory immunoglobulin

  • IgD: regulatory?

  • IgE: functions with parasites and allergens


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IgG (( globulin)

IgG is the principal immunoglobulin of the secondary response.

IgG is the principal immunoglobulin of the adult (but not the neonate.)

IgG constitutes 80% of the circulating immunoglobulin in the adult.

The concentration of IgG in serum is high: 8-16 mg ml-1.

The architecture of IgG is simple:

two ( chains and two 8 chains or

two ( chains and two 6 chains.


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IgM (macroglobulin)

a pentamer (in secreted form) attached by disulfide bonds between the C4 and C3 domains of adjacent heavy chains;

in addition, there is a single J-protein.

IgM is the first immunoglobulin to be synthesized in a primary response.

The concentration of IgM in serum is ~ 1.5 mg ml-1.

IgM is the first immunoglobulin to accumulate in the serum of neonates.

IgM has a high valency which contributes to agglutination. Also, multimeric nature contributes to effective complement activation.

mIgM is a monomer.


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Some visual reinforcement…


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Some more visual reinforcement…


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co-los-trum \kc-‘läs-tram \ n \ [L. beestings] (1577) :milk secreted for a few days after parturition and characterized by high protein and antibody content


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IgA (the secreted antibody…)

Most often a dimer; sometimes a tetramer (or a trimer).

Multimers united by J-protein.

Secretion requires addition of “secretory component” produced in mucosal epithelial cells (in digestive, respiratory, genital, breast tissues and salivary and lacrimal glands).

Plasma cells secrete the Ab;

deliver IgA to epithelial cells having poly-Ig-receptor on their surface.

The poly-Ig-receptor is cleaved and the component that stays associated with IgA is the “secretory component.”

MW = 70,000 daltons; composed of 5 immunoglobulin-like domains;

binds to constant regions of heavy chains.

Movement of the receptor from one surface to another is transcytosis.


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Visual reinforcement…


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IgD is very rare.

0.03 mg ml-1serum

What does this imply?

IgE is extremely rare.

0.0003 mg ml-1 serum

IgE functions against parasites.

In the absence of para-

sites, IgE responds to allergens.

IgD and IgE


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IgE

IgE is extremely rare.

IgE functions against parasites.

In the absence of para-

sites, IgE responds to allergens.


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And, there are subtypes, too


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Hinges versus domains…

  • Hinges contribute to flexibility. They contain cysteine and proline. Cysteine provides interchain linkage. Proline cannot be incorporated into secondary structure.

  • Immunoglobulins without hinge regions have an extra domain.


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Isotypes, allotypes, & idiotypes

  • ISOTYPE: one of the five ((, ", :, *, ,) major kinds of heavy chains in immunoglobulins. Note that the differences among the isotypes are in the constant region.

    Indeed, different isotypes can share common variable regions! (Think about that.)

  • ALLOTYPE: the allelic variation seen at loci specifying the light and heavy chains of immunoglobulins.

  • IDIOTYPE: The set of antigenic determinants (idiotopes) characterizing each unique antibody (or T-cell receptor). Idiotopes are single antigenic determinant(s) in the variable domains of an antibody (or T-cell receptor). Idiotopes are generated by the unique amino acid sequence specific for each antigen.


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Isotypes, allotypes, & idiotypes


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IMPORTANT

  • One B-cell makes one type of antibody.

    (More exactly, one B-cell makes one idiotype.)

  • (This equation is the basis of monoclonal antibodies but we are going to ignore monoclonals for the time being.)

  • Ig’s first appear on the surface of B-cells; there they are selected.

  • The B-cells mature to plasma cells and secrete antibodies with the same specificity (i. e., same idiotypic identity; same antigen specificity.)


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Visual reinforcement…


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Visual reinforcement…

  • The carboxy terminus of the mIg, penetrates into the cytoplasm by only a few amino acids. But mIg is always associated with pairs of the dimer Ig-" / Ig-$.

  • These associated dimers have longer carboxy tails, 61 amino acids and 48 amino acids respectively. The tails contain tyrosine residues which can be phosphorylated by kinases; the phosphorylated or un-phosphorylated states constitute a molecular switch conforming to an on / off switch.

  • (Immunological phenomena affected by kinases tend to use tyrosine as the receptor of phosphates while other cellular phenomena tend to use serine or threonine.)


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Time to review…


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Isotype, allotype, idiotype…

implies that epitopes (at least experimentally) are proteins

proteins are specified by genes

how do genes specify the numerous, diverse, highly specific immunoglobulins? (BIG question!)

Time to review

& take a 5’ break!

Time to review…


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