Absorption of OVA-specific IgG
by breastfed offspring was determined by offspring FcRn expression. Naive C57BL/6J-FcRn+/- females (B6naive) were mated to C57BL/6J-FcRn-/- males. Progeny of this mating were FcRn+/- or FcRn-/-. C57BL/6J OVA-induced AAD (B6AAD) foster mothers were generated (as described in the Methods) and within 24 hours of delivery, pups with or without FcRn were adoptively nursed by B6AAD foster mothers. Serum was collected from FcRn+/+, FcRn+/-, or FcRn-/- offspring at weaning (24 days of life) and 52 days of life (1 week prior to OVA-immunization) and concentrations of OVA-specific Igs were measured by ELISA. OVA-specific Igs were absent from the serum of pups nursed by B6naive mothers (data not shown). Results are presented as 12-19 individual mice per group and the red line is the mean. There were no significant differences in serum concentrations of OVA-specific IgG1 antibodies between FcRn+/+ and FcRn+/- offspring at 24 days or 52 days of life. At 24 days of life, serum OVA-specific IgG1 concentrations were significantly lower in FcRn-/- offspring when compared to FcRn+/+ or FcRn+/- offspring (p ≤ 0.01). At 52 days of life, OVA-specific IgG1 antibodies were no longer detected in the serum of FcRn-/- offspring (limit of detection 30 ng/ml).