Siglec-13

Siglec-13 is a Siglec gene that is present in great apes and other primates but has been deleted in the human lineage, making it a prominent example of species-specific Siglec evolution. In organisms where it exists (such as chimpanzees, gorillas and baboons), Siglec-13 encodes an inhibitory type I transmembrane protein with a V-set sialic acid-binding domain and cytoplasmic ITIM motifs, expressed on monocytes, macrophages and neutrophils, where it recognizes sialylated glycans and modulates innate immune activation. Interestingly, Siglec-13 in macaques has been reported to engage sialylated bacteria (e.g., sialylated strains of group B Streptococcus), restricting bacterial survival and inflammatory responses. The deletion of Siglec-13 in humans, along with other Siglec changes (including Siglec-17 conversion to a pseudogene), has been hypothesized to alter species-specific susceptibility to sialic-acid-decorated pathogens and to contribute to distinctly human inflammatory and infectious disease profiles. Its pseudogenized status is used in evolutionary immunology to dissect the selective pressures shaping the Siglec family.