Figure 3.

The TPKTSVT peptide blocks placental IgG transcytosis. An 18-dpc pregnant mouse was injected i.v. with 100 μg of control GST fusion (A) or TPKTSVT-GST (B). The IgG distribution in the placenta after 6 h of peptide circulation was detected by anti-mouse IgG immunohistochemistry in paraffin sections (brown staining). Strong immunostaining is noted in the vys of mice injected with a control GST fusion (arrowheads) and in the labyrinth of wild-type mice injected with either TPKTSVT-GST or control GST fusion (*) but not in the vys of TPKTSVT-GST fusion (B). Hematoxylin counterstaining is blue. (Bar = 100 μm.) (C and D) A hypothetical model for the TPKTSVT peptide function. Normally, the FcRn/β₂m complex transports IgG from maternal circulation through the labyrinth layer and then the yolk sac placenta (vys) and into the embryo (C). Targeting of the FcRn/β₂m with TPKTSVT peptide can block the receptor complex and the transport of both IgG (B) or phage (Fig. 2D) into the embryo (D).