The chemokine B cell-activating chemokine-1 (BCA-1/CXCL13) is an important homing factor for lymphocytes to B cell zones of secondary lymphoid tissues. CXCL13 acts through its cognate receptor, CXCR5. Normal, mature B cells and a subset of memory T cells express CXCR5 chemokine receptors and migrate in response to BCA-1. However, BCA-1 displays a preferential chemotactic activity for B1 B cells when compared to “normal” B2 B cells. Because B lymphocytes from patients with Chronic Lymphocytic Leukemia (B-CLL) are in several aspects comparable to murine B1 cells, we hypothesized that the CXCR5-CXCL13 axis may be highly active in CLL. Initially, we noticed that CLL cells express functional CXCR5 receptors that induce actin polymerization, CXCR5 endocytosis, chemotaxis, and a prolonged activation of p44/42 MAP kinases. In addition, we examined CXCR5 surface expression in a series of CLL patients by flow cytometry and compared the results with normal B cells, or other leukemic B cell lymphoma. In CLL, leukemia B cells expressed significantly higher surface expression of CXCR5 (mean fluorescence intensity ratio/MFIR: 121 ± 9 (±SEM), n = 26) than circulating, CD19 positive B cells from healthy volunteers (CXCR5-MFIR: 69.9 ± 5.4, n = 11, p = 0.002). Neoplastic B cells from other leukemic B cell lymphomas displayed low surface CXCR5 expression (MFIR 19.7 ± 5.9, n = 11). Serum levels of CXCL13 were evaluated by ELISA. Sera from CLL patients displayed significantly higher levels of CXCL13 (mean ± SEM: 170.1 ± 21.5 pg/ml, n = 22) when compared to sera from healthy volunteers (mean ± SEM: 70.7 ± 5.2 pg/ml, n = 10, p = 0.004). Follicular dendritic cells (FDC) have been considered the main source of CXCL13 in secondary lymphoid tissues, thereby attracting T and B lymphocytes for cognate interactions. Surprisingly, we did not detect significant levels of CXCL13 in supernatants of HK follicular dendritic cells, that previously were demonstrated to protect CLL cells from apoptosis (

Pedersen &Reed, Blood. 2002;100:1795–801
). In contrast, high levels of CXCL13 were detected in supernatants of CLL cell cultures in the presence of nurselike cells (NLC). In NLC cultures, CXCL13 levels were 610 ± 129.8 pg/ml (mean ± SEM, n = 4), whereas FDC supernatants contained 0.22 ± 0 pg/ml CXCL13 (mean ± SEM, n = 2). Because of these high CXCL13 levels in NLC cultures, we examined CXCR5 downregulation on CLL B cells in NLC co-cultures. When compared to freshly isolated CLL B cells, CLL cells from NLC cultures express significantly lower surface CXCR5. CXCR5 MFIR of CLL cells from NLC co-cultures was 7 ± 0.9, n = 4, compared to a CXCR5 MFIR of 91.6 ± 12 for freshly isolated CLL cells the same patients (mean ± SEM, n = 4, p = 0.000). These data indicate that high levels of bioactive CXCL13 are released in NLC cultures that stimulate cognate CXCR5 receptors on CLL B cells and induce signaling cascades, such as p44/42 MAPK, that induce prolonged survival. As such, this study provides a novel insight into interactions between CLL cells and their microenvironment within lymphoid tissues.

Topics:
chemokine cxcl13, chemokine receptors, chemokines, chronic b-cell leukemias, chronic lymphocytic leukemia, ligands, protein overexpression, b-cell lymphomas, coculture techniques, cd19 antigens

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2005, The American Society of Hematology
2005
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