Figure 1. High global prevalence of serum inhibition of Leb binding.

(A) Inhibition (% in white digits) of in vitro binding to human gastric mucosa by H. pylori (Figure S1A) from six individual serum samples (quantified in Figure S1B).

(B) The individual sera IT50 was determined by incubation of H. pylori J166 with ¹²⁵I-Leb-conjugate in a dilution series of serum sample. The dashed vertical lines show the serum dilution when Leb binding was reduced by 50%, i.e., the serum dilution that equals the IT50. Serum from individuals 4–6 did not produce a 50% reduction (Non-Detected (ND) IT50)).

(C) The serum sample from individual 1 lost its blocking activity after IgG affinity desorption (right arrow) (Figure S1C). The IT50/blocking activity was recovered in the IgG fraction from the Protein G affinity column (left arrow).

(D) The sera IT50s of 38 individuals from KI, Sweden (Table S1A). The stars indicate serum samples analyzed in Figure 2A.

(E) The IT50s of 322 individuals from the Swedish Kalixanda study tested by strain 17875/Leb with a median IT50 = 41 and a mean IT50 = 89. The J166 strain was more sensitive because of its lower Leb binding affinity and identified 84% of the sera as IT50 positive (Table S1B and Figure S2B).

(F) The median IT50s of the 322 Kalixanda individuals according to gender and age. The median IT50 was identical between all the men and the women but increased with age (Figures S1Ei and S1Eiv).

(G) The IT50s and H. pylori ELISAs of individuals 10 and 36 from Figure 1D were followed over 26 and 18 years, respectively. The IT50s increased with age during the ~50-year observation period in contrast to the almost constant ELISA titers.

(H) The children’s IT50s tested by strain 17875/Leb varied similarly to adults by 100-1000-fold (Table S1F).

(I) Immunoblot detection of purified native BabA protein and its high-molecular-weight multimers ¹⁴ in the serum sample of individual 10 from KI, Sweden (Figures 1D and 1G) and in the serum samples from world-wide populations (Figure S1H) separated under semi-native conditions (1) or denaturing and reducing conditions (2).