Most microtubules in a cell consist of a simple tube, a singlet microtubule, built from 13 protofilaments. 

TLS Online TPP Program

#Id: 1722

#Unit 4. Cell Communication and Cell Signaling

The α chains of the FcεRI, members of the immunoglobulin superfamily, directly bind the IgE heavy chains, whereas the β and γ chains are responsible for signal transduction.

TLS Online TPP Program

#Id: 1723

#Unit 4. Cell Communication and Cell Signaling

CD23a is found on activated B cells, whereas CD23b is induced on various cell types by the cytokine IL-4.

TLS Online TPP Program

#Id: 1724

#Unit 4. Cell Communication and Cell Signaling

CD23 binds not only to IgE, but also to the complement receptor CD21.

TLS Online TPP Program

#Id: 1725

#Unit 4. Cell Communication and Cell Signaling

Soluble CD23 binds to CD21 on the surface of IgE synthesizing B cells, IgE synthesis is increased.

TLS Online TPP Program

#Id: 1726

#Unit 4. Cell Communication and Cell Signaling

When membrane-bound CD23 binds to soluble IgE, further IgE synthesis is suppressed.

TLS Online TPP Program

#Id: 1727

#Unit 4. Cell Communication and Cell Signaling

FcεRIIB, bear immuno-receptor tyrosine inhibitory motifs Cross-linking of these receptors leads to inhibition, rather than to activation of cellular responses.