Effect of FcRn-TAT peptides on phagocytosis of IgG-opsonized pneumococci. (A) Sequence of the FcRn tail included in the TAT peptides. Signaling motifs of FcRn documented within the FcRn intracellular tail, the tryptophan motif, the 2 aspartic acids, and the dileucine motif are underlined (FcRn WT). Shuffled amino acids in the control peptide with otherwise identical composition are shown in bold (shuffled FcRn). (B) Both wild-type and the shuffled control peptide are translocated over the plasma membrane. Biotinylated TAT peptides were incubated with PMNs. Extracellular staining was done on fixed PMNs, and internalized TAT peptides were detected on fixed and permeabilized cells. (C) WT FcRn-TAT peptides inhibit internalization of IgG1-opsonized bacteria. (D) Control FcRnS peptides had no effect on phagocytosis of IgG1-opsonized pneumococci (experiments were carried out with 0.8 mg/mL TAT peptides). Experiments were repeated 3 times, yielding comparable results. Data in panels C and D represent means plus or minus standard deviations. ^*P < .05; ^**P < .001 when compared with WT.