A Selleck NVP-AUY922 study performed in mice demonstrated that passively acquired maternal antibodies specific for the respiratory syncytial virus suppress antibody responses during primary immunization with live attenuated respiratory syncytial virus vaccine candidates.14 The

passively transferred antibodies did not affect the intensity of the secondary immune response following additional challenge, however. In this study, the authors proposed different mechanisms of antibody-mediated immune suppression, such as blocking or accelerated clearance of the immunizing antigen by binding of the antibodies to specific determinants, or formation of antibody–antigen immune complexes with potent immunoregulatory effects.14 In our experiments, additional alternative mechanisms may be playing a role

in the suppression of immune responses in the offspring, including clonal deletion of B lymphocytes by anti-idiotypic antibodies7 or alteration of T-cell repertoires following the transfer of maternal antibodies.6 Our finding of a reduced T-cell proliferation to FVIII challenge in vitro suggests that maternally transferred IgG may have modified T-cell repertoires in FVIII-deficient mice. However, it is not clear whether the effect on FVIII-specific Alpelisib ic50 T cells occurs directly at the level of T-cell repertoires or through alteration of antigen presentation by antigen-presenting cells, as suggested previously.15 Maternal

IgG are transferred across the placenta to the fetus during gestation and across the proximal small intestine during the neonatal period. Although both systems of IgG transfer occur in humans and rodents, placental transfer is more efficient in humans, whereas transport of maternal IgG in ingested milk across the epithelial cell layer of the proximal small intestine is more efficient in rodents (reviewed Fossariinae in ref. 4). Here, we compared the efficiency of placental versus epithelial transfer of maternal IgG on the anti-FVIII immune response. Our data show that either situation confers protection to the progeny from an early anti-FVIII immune response, although better protection was conferred when maternal anti-FVIII IgG was transferred only during the neonatal period (lactation) rather than during fetal life. While the transfer of maternal anti-FVIII IgG during both pregnancy and lactation had a protective effect on the onset of the anti-FVIII immune response, the protection faded with time and an anti-FVIII immune response could be initiated once the maternally transferred IgG had disappeared from the circulation of the offspring. Furthermore, passive transfer of anti-FVIII IgG to naive mice was also able to delay the immune response to FVIII in these animals, as had been previously observed.