Structures and receptors of the HLA-G molecule. (A) The alternate splicing of a unique primary transcript yields 7 protein isoforms: truncated isoforms are generated by excision of 1 or 2 exons encoding globular (α) domains, whereas translation of intron 4 (i4) or intron 2 (i2) yields soluble isoforms that lack the transmembrane domain. (B) HLA-G molecules can form homodimers through the generation of Cys42-Cys42 disulfide bonds. Reported multimeric structures are presented and referenced. (C) Inhibitory receptors known to bind HLA-G. Basic structural organization and expression patterns are shown. The HLA-G structural configuration that these receptors are known to bind are indicated as follows: − indicates reported absence of binding or minor binding; +, reported binding; and ?, not reported.