Longevity & AgingBlood vessel lining cells add anti-inflammatory sugar caps to antibodies
IgG antibodies carry a sugar group at Asn297 whose terminal sialic acid is thought to dampen inflammation. Sialylated IgG is higher in pregnancy and lower in rheumatoid arthritis, tuberculosis and HIV, but the reason has been unclear. This study found that endothelial cells, not B cells, add sialic acid to IgG. Antibodies taken up by these cells are rescued from degradation by the recycling receptor FcRn. During this recycling, the enzyme ST6Gal1 sialylates them before they return to the blood. Mouse lung endothelial cells and a human endothelial line both did this, while macrophages did not. The capacity is reportedly reduced by inflammatory signals and increased in pregnancy. This suggests the lining of blood vessels can change the function of both natural and therapeutic IgG after it is secreted.
