Adenoviruses and cytomegalo virus use to reduce the surface expression of class I MHC molecules, 

Measles virus and HIV, reduce levels of class II MHC molecules on the surface, 

Vaccinia virus, secreting a protein that binds to the C4b complement component.

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#Unit 4. Cell Communication and Cell Signaling

The cytokines form a family of relatively small, secreted signaling molecules:

Contain about 160–200 AA

4 long, conserved α helices

Control growth and differentiation

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#Id: 9447

#Unit 4. Cell Communication and Cell Signaling

Large family of cytokines:

Interleukins

Interferons

Growth hormone

Prolactin

G-CSF

Thrombopoietin

Erythropoietin

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#Unit 4. Cell Communication and Cell Signaling

Receptor Homodimerization 

Cytokines (erythropoietin) activate receptors by forming dimers of two identical cytokine receptor proteins

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#Unit 4. Cell Communication and Cell Signaling

Receptor hetero-dimerization or hetero-oligomerization 

Other cytokines (interleukins and interferons) bind simultaneously to two or more different cytokine receptors

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#Unit 4. Cell Communication and Cell Signaling

The extracellular domain of cytokine receptors are constructed of two subdomains, each contains seven conserved β strands folded together

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#Unit 4. Cell Communication and Cell Signaling

In cytokine receptors, 

the receptor and kinase are separate polypeptides, encoded by different genes, yet are bound tightly together.