Values represent mean IgG levels, quantified according to a mouse IgG standard curve
Values represent mean IgG levels, quantified according to a mouse IgG standard curve. 2003; Nguyen et al., 2005; Padler-Karavani et al., 2008; Tahara et al., 2010). At the same time, dietary Neu5Gc from foods such as red meat or milk products can be metabolically incorporated into human tissues, particularly epithelia and endothelia (Tangvoranuntakul et al., 2003; Hedlund et al., 2007; Hedlund et al., 2008), through a mechanism involving macropinocytosis and delivery of free Neu5Gc to the cytosol via a lysosomal transporter (Bardor et al., 2005; Yin et al., 2006). Evidently, although the human immune system can react to this xeno-antigen, human biochemical pathways do not see it as foreign. Thus, anti-Neu5Gc antibodies represent novel xeno-autoantibodies, which recognize a non-self animal-derived antigen in the context of self. Indeed, we have recently exhibited that human anti-Neu5Gc antibodies interact with metabolically incorporated Neu5Gc to promote chronic inflammation, likely contributing to tumor progression (Hedlund et al., 2008) and vascular inflammation (Pham et al., 2009). Given their potential contribution to the pathogenesis of dietary Dehydrocostus Lactone red meatCassociated diseases, it is important to understand when and how anti-Neu5Gc antibodies emerge in humans. Here, we show that these antibodies emerge post-natally in humans during the first 12 months of life. Other post-natally acquired human antibodies against foreign glycans, e.g., blood group antibodies and antiC-Gal antibodies, are thought to be induced by commensal bacteria expressing these epitopes (Springer and Horton, 1969; Galili et al., Dehydrocostus Lactone 1988). However, although Cd69 many bacteria can synthesize and express Neu5Ac (Vimr and Lichtensteiger, 2002; Vimr et al., 2004), none are Dehydrocostus Lactone known to synthesize Neu5Gc. Here, we demonstrate that dietary Neu5Gc can be incorporated by a common human commensal bacterium, providing a mechanism for generating anti-Neu5Gc antibodies during the first year of life. To our knowledge, this is the first example in which a diet-derived molecule is usually scavenged by resident bacteria from within the host and effectively expressed as an immunogenic antigen. RESULTS Human anti-Neu5Gc antibodies appear during the first year of life and correlate with the introduction of Neu5Gc in the diet Sera from infants age 0C12 mo (cord, 3 mo, 6 mo, and 12 mo) were analyzed by ELISA for the presence of anti-Neu5Gc IgM and IgG antibodies against Neu5Gc2C6Gal1C4Glc (Gc2C6Lac), an epitope against which most human adults possess high levels of IgM and IgG antibodies (Padler-Karavani et al., 2008). All sera were from infants who had been exclusively breastfed for the first 3 mo of life, and then switched to cows milkCbased formula. Solid foods were also introduced starting at 3 mo of age and included both foods lacking Neu5Gc, such as fruits and vegetables, and Neu5Gc-rich foods, such as beef, pork, and lamb. Anti-Neu5Gc IgM antibodies were absent at birth (cord serum) and at 3 mo, appeared at 6 mo and achieved almost adult levels at 12 mo (Fig. 1 A). As expected because of transplacental transport of IgG, all cord sera contained anti-Neu5Gc IgG antibodies, at levels similar to maternal anti-Neu5Gc IgG. These anti-Neu5Gc IgG antibodies diminished at 3 mo, followed by increasing levels at 6 and 12 mo (Fig. 1 Dehydrocostus Lactone B). There was no difference between male and female anti-Neu5Gc IgM and IgG titers (unpublished data). The reactivity of 12 mo sera against Gc2C6Lac was significantly reduced after truncation of the target epitopes Neu5Gc side chain by moderate periodate oxidation (Tangvoranuntakul et al., 2003), further demonstrating the specificity of the IgG antibodies for Neu5Gc-containing glycans (Fig. 1 C). The absence of anti-Neu5Gc IgM antibodies in cord sera suggests that anti-Neu5Gc antibodies are not germ-line encoded natural antibodies (Ochsenbein and Zinkernagel, 2000), but instead require a postnatal antigenic stimulus. And the early appearance and class switching of these antibodies indicate that humans are exposed to the Neu5Gc antigenic stimulus early in life. The nadir in anti-Neu5Gc IgG titer seen at 3 mo is also consistent with the half-life of maternally derived IgG (Morell et al., 1970), and suggests that these infants lack the production of endogenous anti-Neu5Gc IgG antibodies at 3 mo, when their diets were devoid of Neu5Gc. Interestingly, both infant IgM and IgG anti-Neu5Gc antibodies arise soon after the introduction of Neu5Gc in the diet in the form of cows milk formula and baby foods made up of red meat. Open in a separate window Physique 1. Anti-Neu5Gc antibodies in human infants. (A and B) Levels of anti-Neu5Gc IgM (A) and IgG (B) antibodies in infant.