Figure 1.
Placental transport of IgG subclasses is more efficient for IgG1 and IgG4 than for IgG2 and IgG3.
Blood was collected from mothers just before or after birth and from neonates birth. A) Transport rates for all IgG subclasses expressed as cord/maternal ratios found at birth. The transport rates differed significantly from each other (P<0.0001), except for IgG2 and IgG3 (not significant), as tested by one-way Anova and Tukey's multiple comparison test. (B–E)IgG subclass 1–4 serum levels were quantified by nephelometry and each pair was plotted on a X axis displaying days of each pregnancy against IgG concentration. Average neonate concentration was significantly higher than in the mother for IgG1 and IgG4 as tested by a paired-T test as shown (child/mother ratio = 1.55 and 1.38, respectively) while averge concentrations for IgG2 and IgG3 were not significantly different in mothers and their children (child/mother ratios not significantly different from 1). One pre-term baby was identified displaying low transport of all IgG (square symbol). (F) Child/mother transport ratio of subclasses IgG2-4 for each pair was plotted relative to the IgG1 transport ratios.
Figure 2.
Placental transport efficiency is relatively higher at lower maternal levels.
In general, IgG1 is transported better than IgG4, both of which are transported better than IgG2 and IgG3, which have similar transport rates. Two-tailed Pearson correlation revealed a significant correlation for all subclasses, IgG1 R2 = 0.379, P = 0.0018; IgG2 R2 = 0.2910, P = 0.0096; IgG3 R2 = 0.2415, P = 0.0202; IgG4 R2 = 0.2881, P = 0.0121. Thus, for all subclasses, relatively more IgG was transported at lower maternal IgG.
Figure 3.
Determination of the FcRn binding properties of IgG1 and IgG2 light chain variants.
Binding of titrated amounts of soluble human FcRn (62.5–8000 nM) at pH 6.0 to human IgG variants immobilized onto CM5 sensor flow cells. The relative affinity constants derived (KD) are indicated.
Figure 4.
Validation of IgG1- and IgG2- light chain specific ELISA.
Results from IgG1 total (A) and IgG2 total (B) were plotted against the sum of IgG1κ and IgG1λ, or IgG2κ and IgG2λ, respectively. The results of regression analysis are indicated in each panel, along with Pearson's correlation.
Figure 5.
Equal placental transport of κ and λ of IgG1 and IgG2 subclasses.
IgG1κ (A), IgG1λ(B) and IgG2κ (C) IgG2λ (D) light chain isotype from sera in Fig. 1 were quantified by subclass- and light chain specific ELISA and each mother-child pair was plotted on the x- and y-axis, respectively. A paired t-test revealed no significant difference between the light chains isotypes within each antibody subclass. Average neonate concentration was significantly higher than in the mother for IgG1κ (A) and IgG1λ (B) as indicated in each graph by P values (child/mother ratio = 1.60 and 1.56, respectively) while average concentrations for IgG2 κ and IgG2 λ (C and D) were not significantly different in mothers and their children. (E) Child/mother transport ratio of IgG1λ, IgG2κ and IgG2λ for each pair was plotted relative to IgG1κ transport ratios. While both IgG2 isotypes perform worse than IgG1 when concentration increases, no difference is visible between the IgG2-light chain isotypes.
Figure 6.
No difference in half-life of IgG2 light chain isotypes κ and λ in mice.
(A) Recombinant human IgG2κ and λ in Balb/C mice was injected and measured by total IgG ELISA for a two week period following injection of 200 µg IgG. Calculated half-lives were 7.2±1.48 and 6.4±0.84 days for IgG2κ and IgG2λ. (B) Enrichment of IgG2 κ isoforms was performed as described in Dillon et al 2008. HPLC elution profiles of IgG2 κA and κB structural isomeres on a Dionex ProPac WCX-10 (4.0_250 mm) column are depicted. IgG2κB isoform was generated by incubation of 3 mg/ml IgG2κ in 200 mM Tris buffer at pH 8 with 6 and 1 mM of cysteine and cystamine, respectively. For IgG2κA synthesis 0.9M guanidine hydrochloride (GuHCl) was also added. The samples were kept in the dark and placed at 4°C for 48–72 h. Following incubation the antibody was run on a Zeba spin desalting column (Pierce) for buffer exchange into PBS. (C) The clearance of IgG2λ, IgG2κA, and IgG2κB in Balb/C mice. Calculated half-lives were 4.0±0.58, 5.39±0.85, and 3.7±1.04 days for IgG2κA, IgG2κB and IgG2λ, respectively. (D) Clearance of IgG2κA and IgG2κB in WT and FcγR −/− C57Bl/6 mice. Calculated half-lives were 6.2±2.62, 6.43±1.69, and 7.5±1.89 days for IgG2κA, IgG2κB and IgG2λ, respectively, in WT mice but 1.08±0.28, 1.19±0.23, and 0.7±0.92 days for IgG2κA, IgG2κB and IgG2λ, respectively, in FcRn −/− mice. Graphs in (A, C–D) depict mean and standard deviations of results obtained for 4 mice per group. Half-lives were calculated assuming exponential decay and reported in days ± standard error of means. No significant difference in half-life was detected between the two isotypes.
Figure 7.
Equal placental transport and serum clearance of IgG1 and 2 light chain isotypes κ and λ.
(A) The average IgG1 and IgG2 placental transport (maternal/child) ratios were compared according to their light chain isotype. (B) Clearence of IgG1 and IgG2 κ and λ was investigated in humans by collecting blood from hypogammaglobulinemia patients four weeks after an IVIg transfusion. IgG1 and IgG2 light chain isotypes κ and λ were quantified in serum by subclass- and light chain specific ELISA and subclass composition was compared to that found in the IVIg used. No preferential clearance of one light chain isotype was detectable in either IgG subclass.