Immunoglobulin structure Flashcards Preview

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Flashcards in Immunoglobulin structure Deck (45):
1

IgG

Predominant antibody in the secondary immune response

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IgA

Predominant antibody in external secretions

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IgM

Predominant antibody in primary response

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IgD

Found mainly on the surface of B cells

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IgE

Involvement in allergic hypersensitivities

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Common core structure of all antibodies

Two identical light chains and two identical heavy chains, where each light chain is attached to a heavy chain and the heavy chains are attached to each other

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Immunoglobulin domain

Where all the chains, each of about 110 amino acids in length, all fold independently

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Isotypes of light chain

Either kappa or lambda

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N-terminal region of the heavy and light chains

Variable regions; the rest of them are all constant regions

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Variable region

Combination of the heavy chain variable and light chain variable regions make up the antigen binding region

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Constant region

Carries out other effector functions of the antibody (crossing the placenta, sites for attachment of Fc receptor, complement binding)

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CDRs

Complementarity determining regions - three sites on the variable region above all else determine what will bind

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How are the CDRs exposed?

When they fold, the portions of the CDR in the amino acid sequence stick out as projecting loops

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How is IgM secreted?

In its pentameric form, with a molecular weight of 900,000 daltons

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What joins the subunits of IgM?

The J chain

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IgM is the primary antibody for antigen administered __

parenterally.

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IgM is also the primary antibody elicited by __

T-independent antigen

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How is IgM expressed on B cells?

As a monomer

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Can IgM cross the placenta?

No

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Approximate serum concentration of IgM

100 mg/dL

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IgG is the antibody most characteristic for ___

secondary response

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What is the difference in structure between IgG's secreted and membrane form?

Nothing significant; both monomeric, both ~150,000 daltons

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How does IgG recruit complement fixation?

Varies based on subclass

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Can IgG cross the placenta?

Yes, due to presence of FcRn

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Approximate serum concentration of IgG

1200 mg/dL

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Typical form of IgD

Membrane form

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Function of IgD

B cell antigen receptor along with IgM

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Serum concentration of IgD

3 mg/dL

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To what types of cells does IgE bind?

Mast cells and basophils due to Fc receptor

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How is IgE secreted?

As a CHO-rich monomer of 190,000 daltons

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Serum concentration of IgE

30 mcg/mL

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How does predominant IgA occur?

As a dimer

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How are the subunits of IgA joined?

By the J chain

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How does serum IgA occur?

As a monomer (function is unclear)

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Can IgA cross the placenta?

No

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How does it fix complement?

Through alternative pathway

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Serum concentration of IgA

300 mg/dL

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IgA plays a crucial role in __

mucosal immunity

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How do antibodies contribute to the immune response?

By binding to and neutralizing pathogens, as well as signalling for destruction by other cells

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Fc-receptor mediated killing

If antibodies don't neutralize the pathogen, the Fcs on the antibodies will signal to FcRs on macrophages, eosinophils, NK cells, basophils, and mast cells, and they'll kill it

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Neonatal antibody production

IgG: maternal IgG for the first few months, then reaches adult levels at age 4
IgM: adult levels reached at age 10 months
IgA: adult levels reach at 10 years old

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Clinical use of immunoglobulins: polyclonal and monoclonal antibodies

Polyclonal is found in immunized individuals. Monoclonal can be used in vitro to keep passive antibodies

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Examples of polyclonal antibody uses

IVIG treatment for inflammatory diseases

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Examples of monoclonal antibody therapy

Tumor-specific antibodies to treat cancer

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Immunoglobulin classes are distinguished based on __

the constant region of the heavy chain.