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CHAPTER 13

ii.

Band p25 on chromosome 6 con-
taining the interferon regulatory
factor 4 gene [t(14;6) (q32;p25)].

iii. Band q13 on chromosome 11 con-

taining the cyclin D1 gene [t(14;11)
(q32;q13)].

iv. Band q23 on chromosome 16 con-

taining the C-MAF transcription
factor [t(14;16) (q32;q23)].

b.

A common mechanism by which
these translocations may lead to MM
is unknown.

c.

MM is characterized by the malignant
proliferation of plasma cells within
the bone marrow compartment.

d.

The malignant plasma cells produce
high levels of a single monoclonal im-
munoglobulin or free 

 chains or 

chains (called Bence-Jones proteins)
in the serum or urine.

e.

MM is the most common type of
monoclonal gammopathy.

f.

Clinical signs include high susceptibil-
ity to bacterial and viral infections
since normal immunoglobulin synthe-
sis is suppressed; back and chest bone
pain; bone resorption; weakness and
fatigue associated with anemia; pallor;
radiculopathy; and renal failure.

● Figure 13-6 Multiple Myeloma.

g.

Laboratory findings include large, waxy, laminated casts in the renal tubules;
hypercalcemia; normocytic, normochromic anemia; rouleaux formation; and
demonstration of monoclonal Ig (M proteins; called the “M spike”) in the
serum or urine by electrophoresis.

h.

The top lateral radiograph shows multiple lytic lesions in the calvarium. The
bottom light micrograph shows bone marrow from a patient with MM. Note
the sheet of atypical plasma cells which vary in size and shape.

B. CENTRAL NERVOUS SYSTEM (CNS) DISORDERS

1.

Multiple sclerosis (MS; Figure 13-7)

a.

MS is caused by unknown mechanisms.

b.

MS is an autoimmune disease of the CNS and is characterized by multifocal
areas of demyelination with relative preservation of axons, loss of oligoden-
drocytes, and astroglial scarring.

c.

MS results in paralysis, loss of sensa-
tion, and loss of coordination al-
though the exact nature of the defect
depends on the specific area of the
CNS involved.

d.

Clinical signs include the following:
affects primarily women of Northern
European descent of childbearing age
(15–50 years of age); fatigue; sensory
loss in limb; visual loss; subacute
motor loss; diplopia; polysymptomatic

● Figure 13-7 Multiple Sclerosis.

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99

MOLECULAR BIOLOGY OF THE IMMUNE SYSTEM

onset; relapses and remissions; optic neuritis; and Lhermitte’s sign (sudden,
transient, electric-like shocks spreading down the body when the patient flexes
the head forward).

e.

Laboratory findings include the following: cerebral or spinal plaques which
consist of a discrete region of demyelination with relative axonal preservation
is seen on MRI; active plaques show perivascular infiltration of T cells and
macrophages with occasional plasma cells; gadolinium-DPTA is a paramag-
netic contrast agent that crosses a disrupted blood-brain barrier and is used to
assess plaque activity (new or newly active plaques accumulate gadolinium);
oligoclonal bands which represent limited classes of immunoglobulins (de-
picted as discrete bands on agarose gels) are found in 85%–95% of MS patients;
antimyelin antibodies may correlate with MS activity or predict progression
from a clinically isolated event to MS although the data are conflicting.

f.

The photograph shows a coronal section of the brain with prominent de-
myelinated plaques (arrows).

2.

Myasthenia gravis (MG)

a.

MG is caused by unknown mechanisms.

b.

MG is an autoimmune disease of the skeletal muscles involving the nicotinic
acetylcholine receptor (nAChR) located at the neuromuscular junction.

c.

MG is characterized by weakness and fatigability of skeletal muscles.

d.

Clinical signs: affects women of 20–30 years of age or men older than 60 years 
of age; fatigue as the degree of muscle weakness increases with exercise and 
improvement with rest; muscle weakness often begins with the ocular muscles–
however, the facial muscles or limbs muscles may also be initially affected;
ptosis; diplopia; “myasthenic snarl” may be observed when facial muscles are
affected; nasal speech; difficulty in swallowing; thymic hyperplasia; and thy-
moma.

e.

Laboratory findings: anti-nAChR antibodies are present and mediate the phys-
ical symptoms; the anti-nAChR antibodies belong to the IgG

1

and IgG

3

sub-

classes and therefore fix complement; the anti-nAChR antibodies may be
directed against any of the five subunits of the nAChR; some patients who are
anti-nAChR negative have anti–muscle-specific receptor tyrosine kinase.

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Chapter

14

Molecular Biology Techniques

100

cut or nick site

T AGCGGCCA T C

A T CGCCGGT AG

GA T GGCCGC T A

C T ACCGGCGA T

5'

3'

3'

5'

Nontemplate

Template

Palindrome

Palindrome

C

Cut DNA with

Mst II and hydridize
with 

β

-globin probe

β

S

 (1.3 kbp)

β

A

 (1.1 kbp)

M

(

AS)

F

(

AS)

C

(

AA)

Fetus

(SS)

Site absent
in sickle-cell

β

-globin

MstII Mst II

MstII

1.1 kbp

1.3 kbp

Normal

D

B

A

Sickle cell

● Figure 14-1

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MOLECULAR BIOLOGY TECHNIQUES

Action of Restriction Enzymes.

Restriction enzymes (REs) are bacterial enzymes that catalyze

the hydrolysis of the phosphodiester bond in the DNA molecule (i.e., cut the DNA) at specific
nucleotide sequences (4–10 base pairs long). These enzymes are crucial to DNA technology
because treatment of a DNA sample with a particular RE will always produce the same pattern of
DNA fragments.

Figure 14-1A Action of EcoR1, Alu1, and HindIII. The action (i.e., hydrolysis of the phospho-

diester bond) of REs EcoR1, Alu1, and HindIII is shown. The specific nucleotide sequences that
each RE recognizes and its cut site (

▲

) is indicated. Note that EcoR1 and HindIII produce DNA

fragments with staggered ends, whereas Alu1 produces DNA fragments with blunt ends.

Figure 14-1B Action of EcoR1 and Alu1 on a long piece of DNA. A long piece of DNA will

have many cut sites. If this long piece of DNA is treated with both EcoR1 and Alu1, the four DNA
fragments indicated will always be produced due to the specificity of the REs. You may be asked
on the USMLE to deduce the DNA fragments produced in an RE reaction.

Figure 14-1C Palindromes (or inverted repeat sequences). Palindromes are two identical base

sequences on different strands on the DNA (i.e., nontemplate strand and template strand) and run-
ning in opposite directions (or read the same in the 5

 S 3 direction).

Figure 14-1D Direct detection of the sickle cell anemia mutant 

-globin gene:

• Sickle cell anemia is an autosomal recessive genetic disease caused by a mutation in the 

-

globin gene that results in a change of single amino acid from glutamic acid (normal) to valine
(mutant) in the 

-globin protein.

• The base change (A S T) destroys the recognition sequence for a number of REs, including

MstII.

• MstII cuts the normal 

-globin gene into two fragments, 1.1 and 0.2 kb.

• MstII cuts the mutant 

-globin gene into one 1.3 kb fragment because the A S T base change

destroys one of the MstII cut sites.

• A Southern blot can be performed on the MstII cut DNA and hybridized with a 

-globin probe.

The Southern blot shows the prenatal diagnosis of sickle cell anemia using the MstII polymor-
phism. The mother (M) and father (F) are heterozygote (AS) carriers of sickle cell anemia
because they show the l.l and 1.4 kb fragments. Their normal child (C) is homozygous (AA)
because he shows only the 1.1 kb fragment. Their fetus is homozygous (SS) and will have sick-
le cell anemia because the fetus shows only the 1.3 kb fragment.

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102

CHAPTER 14

Agarose Gel

● Figure 14-2

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