Molecular analysis of Ig class switching in IgA+ and IgG+ memory B-cell subsets. (A) Schematic representation of the constant region of the human IGH locus. (B) Distribution of IgA and IgG receptor subclass use in IGH rearrangements of class-switched memory B-cell subsets. Total number of analyzed sequences is indicated in the center of each plot. Differences in the distribution were statistically analyzed with the χ2 test and were found significant for both CD27+IgG+ vs CD27−IgG+ (P < .0001) and CD27+IgA+ vs CD27−IgA+ (P < .05) B-cell subsets. (C) Frequency of Sμ-Sα and Sμ-Sγ rearrangements bearing remnants of indirect class switching. Number of analyzed sequences is given in brackets. (D) Examples of direct and sequential class switching; a piece of Sγ3 sequence in the Sμ-Sγ2 junction is indicated boxed in red font.
