Fig. 2.

Different tetraspanins in non-activated and activated MCs. Majority of tetraspanins is expressed on MCs surface with exception of CD63 that is expressed also on MCs preformed granules in non-activated MCs. MCs contain preformed granules and form multi-vesicular bodies that give rise to exosomes. Stimulation with IgE/Ag complexes leads to release of several mediators including histamine, proteases, cytokines, as well as exosomes and, probably, redistribution of tetraspanins. Whether MC tetraspanins are involved in regulation of c-kit, TLR, or GPCR-mediated signals is unknown. MCs’ exosomes contain several proteins, RNAs and DNAs and tetraspanins CD9, CD63, and CD81 were identified on their surface. Antibodies against several tetraspanins were found to inhibit degranulation (αCD63 and αCD81) or chemotaxis (αCD9). On the other hand, loss of CD63 leads to decreased degranulation and TNFα release, whereas loss of CD151 potentiates cytokine production