Molecular Mimicry May Contribute to Autoimmune Disease

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For several reasons, the notion that microbial or viral agents might play a role in autoimmunity is very attractive. It is well accepted that migrant human populations acquire the diseases of the area to which they move and that the incidence of autoimmunity has increased dramatically as populations have become more mobile. This, coupled with the fact that a number of viruses and bacteria have been shown to possess

Molecular mimicry between proteins of infectious organisms and human host proteins

Protein*

Residue'

Sequence*

Protein*

Residue'

Sequence*

Human cytomegalovirus IE2

79

P

D

P

L

G

R

P

D

E

D

HLA-DR molecule

60

V

T

E

L

G

R

P

D

A

E

Poliovirus VP2

70

S

T

T

K

E

S

R

G

T

T

Acetylcholine receptor

176

T

V

I

K

E

S

R

G

T

K

Papilloma virus E2

76

S

L

H

L

E

S

L

K

D

S

Insulin receptor

66

V

Y

G

L

E

S

L

K

D

L

Rabies virus glycoprotein

147

T

K

E

S

L

V

I

I

S

Insulin receptor

764

N

K

E

S

L

V

I

S

E

Klebsiella pneumoniae nitrogenase

186

S

R

Q

T

D

R

E

D

E

HLA-B27 molecule

70

K

A

Q

T

D

R

E

D

L

Adenovirus 12 E1B

384

L

R

R

G

M

F

R

P

S

Q

a-Gliadin

206

L

G

Q

G

S

F

R

P

S

Q

Human immunodeficiency virus p24

160

G

V

E

T

T

T

P

S

Human IgG constant region

466

G

V

E

T

T

T

P

S

Measles virus P3

13

L

E

C

I

R

A

L

K

Corticotropin

18

L

E

C

I

R

A

C

K

Measles virus P3

31

E

S

D

N

L

G

Q

E

Myelin basic protein

61

E

S

F

K

L

G

Q

E

*In each pair, the human protein is listed second. The proteins in each pair have been shown to exhibit immunologic cross-reactivity. *Each number indicates the position on the intact protein of the amino-terminal amino acid in the listed sequence. ^Amino acid residues are indicated by single-letter code. Identical residues are shown in blue. SOURCE: Adapted from M. B. A. Oldstone, 1987, Cell 50:819.

*In each pair, the human protein is listed second. The proteins in each pair have been shown to exhibit immunologic cross-reactivity. *Each number indicates the position on the intact protein of the amino-terminal amino acid in the listed sequence. ^Amino acid residues are indicated by single-letter code. Identical residues are shown in blue. SOURCE: Adapted from M. B. A. Oldstone, 1987, Cell 50:819.

antigenic determinants that are identical or similar to normal host-cell components led Michael Oldstone to propose that a pathogen may express a region of protein that resembles a particular self-component in conformation or primary sequence. Such molecular mimicry appears in a wide variety of organisms (Table 20-3). In one study, 600 different monoclonal antibodies specific for 11 different viruses were tested to evaluate their reactivity with normal tissue antigens. More than 3% of the virus-specific antibodies tested also bound to normal tissue, suggesting that molecular mimicry is a fairly common phenomenon.

Molecular mimicry has been suggested as one mechanism that leads to autoimmunity. One of the best examples of this type of autoimmune reaction is post-rabies encephalitis, which used to develop in some individuals who had received the rabies vaccine. In the past, the rabies virus was grown in rabbit brain-cell cultures, and preparations of the vaccine included antigens derived from the rabbit brain cells. In a vaccinated person, these rabbit brain-cell antigens could induce formation of antibodies and activated T cells, which could cross-react with the recipient's own brain cells, leading to encephalitis. Cross-reacting antibodies are also thought to be the cause of heart damage in rheumatic fever, which can sometimes develop after a Streptococcus infection. In this case, the antibodies are to streptococcal antigens, but they cross-react with the heart muscle.

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