The spontaneous recruitment of B cells into GCs of the GALT in LMP2A mice predicts that B cells can be driven into these structures in the absence of specific antigen recognition. To test this hypothesis, we analyzed three inde-
Fig. 3 Spontaneous GCs in PP of three independent BCR transgenic mice as revealed by flow cytometric analyses. Shown are CD19+ gated B cells. Percentages ofboxed GC B cells within the CD19+ B cell gate are indicated pendent transgenic mouse strains expressing non-autoreactive prerearranged IgH + IgL chain genes (Casola et al. 2004). In one strain of mice (MD4) the specificity of the BCR receptor is known (hen egg lysozyme), in the other two (B1-8Hí;3-83kí, and B1-8Hí;D23kí) no specific antigen has been so far identified. In all three BCR transgenic mouse strains the vast majority of the peripheral B cells expressed the original BCR specificity. Spontaneous GCs were observed in PP and MLN of all three transgenic strains (Fig. 3). The fraction of GC B cells was comparable to that of wild-type mice. Importantly, molecular analysis of sorted GC and non-GC B cells of PP of the three transgenic strains excluded the possibility that B cells in the GALT GCs of these animals were selected on the basis of the expression of a second BCR generated through secondary IgL chain rearrangements (Casola et al. 2004). These results support the concept that efficient recruitment of B cells into GALT GCs can occur in the absence of antigen recognition through the BCR.
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