Human IgE does not bind to human FcRn

Abstract

The neonatal Fc receptor (FcRn) is known to mediate placental transfer of IgG from mother to unborn. IgE is widely known for triggering immune responses to environmental antigens. Recent evidence suggests FcRn-mediated transplacental passage of IgE during pregnancy. However, direct interaction of FcRn and IgE was not investigated. Here, we compared binding of human IgE and IgG variants to recombinant soluble human FcRn with β2-microglobulin (sFcRn) in surface plasmon resonance (SPR) at pH 7.4 and pH 6.0. No interaction was found between human IgE and human sFcRn. These results imply that FcRn can only transport IgE indirectly, and thereby possibly transfer allergenic sensitivity from mother to fetus.

Figure 1

Confirmation of antibody integrity and antigen binding in SPR. (A) HPLC-SEC chromatograms of the IgG variants as relative UV280 nm signal normalized to maximum response. The chromatograms of molecules overlap. (B) SDS-PAGEs under non-reducing (NR) and reducing (R) conditions. Shown are two independently prepared SDS-PAGEs of purified V-gene matched IgG variants (left) and the IgE supernatant (right). The uncropped original images showing the relevant gel parts can be found in Supplementary Fig. 1A and B, respectively. (C) IgE-specific Western Blot after native PAGE of anti-biotin IgE supernatant next to contact allergy serum sample. The uncropped original image showing the relevant lanes can be found in Supplementary Fig. 1C. (D) Schematic overview of SPR experiments showing anti-biotin antigen binding and presence of human IgE in culture supernatants. (E) Sensorgrams of one representative of three independent experiments showing binding of anti-IgE antibody (left) and soluble FcεRI (right) at pH 7.4 and pH 6.0 after capturing anti-biotin IgE from culture supernatant in comparison to IgG at 100 nM.

Figure 2

Titration of human sFcRn in SPR reveals no binding to IgE at pH 7.4 or 6.0. Anti-biotin IgG variants and IgE were captured on a sensor with different concentrations of BSA-biotin spotted, leading to comparable levels of antigen-bound IgG and IgE (not shown due to blank subtraction). Human sFcRn was injected in a twofold serial dilution covering a concentration range from 15.63 to 1000 nM and K_D values were calculated fitting a 1:1 Langmuir binding model after blank subtraction. A representative of three independent experiments is shown.