Anti-Neu5Gc antibodies in human infants. (A and B) Levels of anti-Neu5Gc IgM (A) and IgG (B) antibodies in infant sera (n = 15, filled circles) from birth (cord), 3, 6, at 12 mo (for each infant) and adult sera from the pregnant mothers (n = 9, open squares) were measured by ELISA against Neu5Gcα2–6Lacβ–HSA. Each data point represents the mean of triplicate values from one individual, quantified according to an IgM or IgG standard curve. Horizontal lines represent mean values for each group. (C) Neu5Gcα2–6Lacβ–HSA coated on an ELISA plate was treated with mild periodate (periodate) or inactivated periodate (mock periodate), and then analyzed for binding by IgG antibodies from infants at 12 mo of age (n = 15). Bars represent mean absorbance values at OD₄₉₀ ± SEM. Statistical analysis was performed using an unpaired two-tailed Student’s t test. (D) Infant sera (same infants as in A and B) were analyzed by ELISA for IgM antibodies against α-Gal-PAA (dashed line). For comparison, anti-α-Gal IgM levels were plotted with anti-Neu5Gc IgM levels (solid line; same data as in Fig. 1 A). Values represent mean IgM levels ± SEM.