Page 538 - Review of Medical Microbiology and Immunology ( PDFDrive )

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mebooksfree.com mebooksfree.com A. Serum IgA H L Monomer mebooksfree.com L H mebooksfree.com mebooksfree.com
CHAPTER 59 Antibodies
527
Dimer

H
L component J chain H L H
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mebooksfree.com mebooksfree.com B. Secretory IgA (dimer) J chain mebooksfree.com mebooksfree.com mebooksfree.com
L
Secretory

H
L

H L J chain
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C. IgM (pentamer)

H
L

FIGURE 59–4 Structure of serum immunoglobulin (Ig) A (A), secretory IgA (B), and IgM (C). Note that both IgA and IgM have a J chain
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but that only secretory IgA has a secretory component. (Reproduced with permission from Stites D, Terr A, Parslow T, eds. Basic & Clinical Immunology. 8th ed.
Originally published by Appleton & Lange. Copyright 1994 McGraw-Hill.)
ISOTYPES, ALLOTYPES, &
their H chains is different), and κ and λ chains are different
IDIOTYPES
isotypes (their constant regions also differ antigenically).
(2) Allotypes, on the other hand, are additional anti-
Because immunoglobulins are proteins, they are antigenic,
genic features of immunoglobulins that vary among
and that property allows them to be subdivided into iso-
types, allotypes, and idiotypes.
individuals. They vary because the genes that code for
(1) Isotypes are defined by antigenic (amino acid) dif-
have different alleles. For example, the λH chain con-
ferences in their constant regions. Although different anti-
tains an allotype called Gm, which is due to a one– or
genically, all isotypes are found in all normal humans. For the L and H chains are polymorphic, and individuals can
two–amino acid difference that provides a different anti-
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example, IgG and IgM are different isotypes; the constant
genicity to the molecule. Each individual inherits differ-
region of their H chains (γ and μ) is different antigenically
ent allelic genes that code for one or another amino acid
(the five immunoglobulin classes—IgG, IgM, IgA, IgD, and
5
IgE—are different isotypes; their H chains are antigenically
different). The IgG isotype is subdivided into four sub-
5
Allotypes related to λH chains are called Gm (an abbreviation of
types, IgG1, IgG2, IgG3, and IgG4, based on antigenic dif-
gamma); allotypes related to κL chains are called Inv (an abbreviation of
ferences of their heavy chains. Similarly, IgA1 and IgA2 are
a patient’s name).

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