Session: 203. Lymphocytes, Lymphocyte Activation, and Immunodeficiency, including HIV and Other Infections: Poster III
Hematology Disease Topics & Pathways:
Biological Processes, hematopoiesis, immune mechanism
The GC B-cells are thought to be the cell-of-origin of diffuse large B-cell lymphoma (DLBCL). To determine if the loss of Kmd6a could impact the mature B cells undergo germinal center (GC) reaction, we immunized the young, female Kdm6a-null mcie and wildtype littermates with T cell-dependent antigen sheep red blood cell (SRBC). Mice were scrificed 14 days after immunization, spleen cells were examined by flow cytometry. As expected, we observed a significant increase in the percentage of GC B cells (B220+GL7+CD95+) from female Kdm6a-null mice compared to control mice. We also observed differences in the percentage of other B-cell subsets between these mice, including an increase in plasma cells (B220-CD138+) and memory B cells (B220+CD19+CD27+), concomitant with an increase trend towards the elevated marginal zone B cells (B220+CD23loCD21+) and transitional B cells (B220+CD23-CD21-). In contrast, there was a decrease in the follicular zone B cells (B220+CD23-CD21-) and plasmablast (B220+CD138+). To analyze the levels of SRBC-specific Abs from immunized mice, serum was collected from blood at day 14. A flow cytometry-based assay was performed to detect the fluorescent-labeled SRBC-specfic Abs for immunoglobulin. Results showed that the abundance of non-class-switched anti-SRBC IgM level was significantly increased in female Kdm6a-null mice serum compared with control mice. In contrast, these mice had significantly decreased anti-SRBC IgA, IgG, IgG1, IgG3 and IgE levels indicating a isotype class switch defect.
The aberrant GC phenotype induced by SRBC indeicated that kdm6a loss results in expansion of GC B cells, which subsequently enhances the plasma cell generation. This finding prompted us to investigate if the Kdm6a impairs the immunoglobulin affinity maturation. Therefore, we analyzed the ability of female Kdm6a-null mice and wildtype littermates to generate specific Abs against another T cell-dependent antigen NP-Chicken Gamma Globulin (NP-CGG). Mice were immunized with NP-CGG (29) and serum were collected weekly up to 8 weeks total. ELISA analysis of serum revealed that NP-specfic total Ig level were similar for both groups of mice over time. However, consistent with the SRBC immunization results, we did observed a sinificant reduction in the titers of NP-specific IgA and IgG1 Abs in female Kdm6a-null mice compared with control mice at each time point, while these mice had a sinificant increase in NP-specific IgM Abs, which indicating the loss of Kdm6a disrupts the balance between non-class-switched and class-switched NP-specific Abs isotypes (Figure 1A-D). Likewise, we also observed an increase in the percentage of GC B cells and plasma cells 8 weeks after NP-CGG immunization by flow cytometry. Again, our findings indicate the loss of Kdm6a causes germinal center hyperplasia, enhances plasma cell differentiation, and likely impairs class switch recombination (CSR).
Taken together, our data shows that Kdm6a plays an important, but complex, role in B-cell transiting in the GC reaction and that loss of Kdm6a causes germinal center hyperplasia and impedes the B-cell immune response in a specific manner that may contribute to infection and B-cell malignancies.
Disclosures: Wartman: Novartis: Consultancy; Incyte: Consultancy.
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