Figure 3.

Semaphorin receptors. Members of the plexin protein family are organized into four classes (A, B, C, and D); plexins are known to bind to semaphorins from all classes except class 2, whose receptors are unknown. Class 3 semaphorins bind both members of the neuropilin protein family. Sema4A binds Tim-2, a member of the T cell, immunoglobulin and mucin (Tim) domain protein family expressed on activated T cells [27]. Sema 4D binds CD72, a member of the C-type lectin family, and uses it for its effects in lymphoid tissues [27]. Sema, semaphorin; PSI, plexin-semaphorin-integrin; IPT, immunoglobulin-like fold shared by plexins and transcription factors; GAP, GTPase-activating protein; MAM, Meprin, A5, Mu; PMR, polymorphic region; ITIM, immunoreceptor tyrosine-based inhibitory motif; IgV, immunoglobulin variable region.