Differential representation of B cell subsets in mixed bone marrow chimera mice due to expression of allelic variants of CD45 (CD45.1/CD45.2)

The CD45 congenic marker system is a highly utilized technique to track hematopoietic cells following bone marrow transplantation (BMT), with CD45.1 and CD45.2 being efficiently distinguished by flow cytometry. During the analysis of control mixed BM chimera mice in which lethally irradiated recipients were transplanted with an equal number of BM cells from WT CD45.1 and WT CD45.2 mice, we observed an unequal reconstitution of specific B cell subsets in the bone marrow (BM), lymph node (LN) and spleen. Specifically, in the BM and LN, there was an increase in the percentage of CD45.2 mature B cells. In the spleen, an increase in the percentage of CD45.2 transitional (T) 1 and T2 cells was observed. In contrast, the percentage of splenic CD45.1 marginal zone (MZ) B cells was significantly increased. When we compared the percentage of B cell subsets in unmanipulated WT CD45.1 and WT CD45.2 mice, we found that WT CD45.2 mice had significantly more LN B cells while WT CD45.1 mice exhibited an increase in MZ B cells. These data indicate that the alteration in the ratio of CD45.1 and CD45.2 B cell subsets in mixed chimera mice is a cell-intrinsic effect. Thus whenever the CD45 congenic system is used to track two genetically distinct populations of immune cells WT chimeras must be generated to allow normalization of the experimental data to avoid the reporting of unintentionally skewed data.