Blood levels of Der f-sIgG (total) in 31 subjects and their correlation with (A) subject age (P<0.05); (B) Der f-sIgE level; and (C) Der f-sIgG4 level. In the panel C, IgG4 levels of five subjects with less than the limit of detection (0.1 µg/mL) were assumed to be 0.05 µg/mL for convenience. The red and blue arrows indicate extreme cases of Der f-sIgG levels (highest and lowest, respectively). In panel A, the case with the lowest (undetectable) Der f-sIgG levels (73-year-old woman, potential non-responder against Der f) was excluded from the regression analysis.