UC San Diego

All human adults have circulating antibodies against N- glycolylneuraminic acid (Neu5Gc), a sialic acid absent in humans. Neu5Gc from foods of mammalian origin can be metabolically incorporated into human tissues, especially vascular endothelia and carcinomas. Thus, the potential exists for circulating anti-Neu5Gc "xeno-autoantibodies" to react against this exogenously incorporated "self" Neu5Gc. Indeed, recent studies have demonstrated that anti -Neu5Gc antibodies can contribute to tumor progression and vascular inflammation. This dissertation focuses on investigating the origins and other implications of these anti-Neu5Gc antibodies. Chapter 2 of this dissertation describes a novel model in which resident bacteria cooperate with dietary Neu5Gc to generate anti-Neu5Gc antibodies in humans. We show that anti-Neu5Gc antibodies appear during infancy and correlate with the introduction of Neu5Gc in the diet. However, dietary Neu5Gc alone is insufficient to elicit anti-Neu5Gc antibodies in human- like Neu5Gc deficient (Cmah-null) mice. While other postnatally-appearing anti-carbohydrate antibodies are likely induced by colonizing bacteria, no microbe is known to synthesize Neu5Gc. Here we show that anti-Neu5Gc antibodies appear coincident with antibodies against non- typeable Haemophilus influenzae (NTHi), an obligate human commensal and pathogen. We show that trace exogenous Neu5Gc can be incorporated into cell surface LOS molecules, which induce anti-Neu5Gc antibodies in Cmah-null mice. Furthermore, purified human anti-Neu5Gc antibodies specifically recognize Neu5Gc-expressing NTHi. Finally, Neu5Gc from infant foods is taken up and expressed by NTHi. We propose that incorporation of dietary Neu5Gc by NTHi residing in the nasopharynx can induce the production of anti-Neu5Gc antibodies in humans. Cmah-null mice immunized with Neu5Gc-expressing NTHi generate anti-Neu5Gc antibodies with similar titer and specificity to humans. Chapters 3 and 4 describe two projects that use these mice to study the significance of anti-Neu5Gc antibodies. These two projects demonstrate that anti-Neu5Gc antibodies can contribute to enhanced clearance of Neu5Gc-containing biotherapeutics and reproductive incompatibility, respectively. Chapter 5 details preliminary studies investigating the differential utilization of human and non-human sialic acids by NTHi. Here we investigate sialic acid expression preferences of NTHi and analyze sialic acid catabolism preferences of the NanA lyase. Finally, we present evidence that Neu5Gc utilization by NTHi has intriguing consequences for growth and survival in human serum