Summary The disturbed erythropoiesis in patients with refractory anaemia with ring‐sideroblasts (RARS) is characterized by intramedullary apoptosis of erythroid precursors and increased iron accumulation in mitochondria. To gain insight into these pathophysiological mechanisms we compared the gene expression profile (GEP) of erythroid precursors from RARS patients to the GEP of normal erythroid precursors. Three hundred sixty four probe sets were up‐, and 253 probe sets downregulated in RARS cells. Interestingly, Growth Differentiation factor 15 (GDF15), a cytokine from the TGFβ family, was dramatically upregulated in all RARS patients. Measurement of GDF15 in the sera from twenty RARS patients confirmed this finding by showing significantly, 7·2‐fold, increased protein levels (3254 ± 1400 ng/ml vs. 451 ± 87 ng/ml in normals). In vitro studies demonstrated erythroid‐specific production of GDF15 and dependence on erythropoietin. Induction of apoptosis by arsenic trioxide, a drug which acts via reduction of the mitochondrial membrane potential, also stimulated GDF15 production. Downregulation of endogenous GDF15 production in erythoblasts by specific siRNA led to diminished erythroid differentiation. Taken together, our findings demonstrate a new role for GDF15 in normal erythropoiesis as well as in the ineffective erythropoiesis of RARS patients.

No abstract

Differentiation of naive B cells into plasma cells or memory cells occurs in the germinal centers (GCs) of lymph follicles or alternatively via a GC- and T-cell-independent pathway. It is currently assumed that B-cell lymphomas correlate to normal B-cell differentiation stages, but the precise correlation of several B-cell lymphomas to these two pathways remains controversial. In the present report, we describe the junctional adhesion molecule C (JAM-C), currently identified at the cell-cell border of endothelial cells, as a new B-cell marker with a tightly regulated expression during B-cell differentiation. Expression of JAM-C in tonsils allows distinction between two CD27+ B-cell subpopulations: JAM-C- GC B cells and JAM-C+ non-germinal B cells. The expression of JAM-C in different B-cell lymphomas reveals a disease-specific pattern and allows a clear distinction between JAM-C- lymphoproliferative syndromes (chronic lymphocytic leukemia, mantle cell lymphoma and follicular lymphoma) and JAM-C+ ones (hairy cell leukemia, marginal zone B-cell lymphoma). Therefore, we propose JAM-C as a new identification tool in B-cell lymphoma diagnosis

No abstract

3940 Poster Board III-876 Introduction Differentiation of naïve B cells into plasma cells or memory cells occurs in the germinal centres (GC) of lymph follicles or alternatively in the marginal zone via a GC- and T cell independent pathway. It is currently assumed that B cell lymphomas correspond to normal B cell differentiation stages, but the precise correlation of several B cell lymphomas to these two pathways remains controversial. We have previously shown that junctional adhesion molecule C (JAM-C) originally identified at the cell-cell border of endothelial cells, constitutes also a marker of B lymphocytes with a tightly regulated expression during B cell differentiation: immature B cells, GC-B cells and plasma cells stain negatively, whereas mature, memory and marginal zone derived B cells stain strongly positive. Here we test the expression of JAM-C on a series of patients with B cell lymphomas. Methods B lymphocytes from the peripheral blood of 158 untreated patients were analyzed using flow cytometry with standard antibody panels (CD5, CD10, CD11c, CD22, CD23, CD25, CD38, CD103, FMC7, sIg). Diagnosis of a B cell lymphoma was established according to WHO guidelines, using additionally RT-PCR, karyotyping, or FISH, if necessary. Expression of JAM-C was studied by flow cytometry with a polyclonal antibody obtained from a rabbit immunized with the soluble JAM-C molecule. Results MCL, HCL and MZBL with a supposed origin in the marginal zone stained mostly positive, whereas CLL and FL with a supposed origin in the germinal centre showed mostly a negative staining. No correlation was found in CLL between JAM-C expression and staining for ZAP70 or CD38. In 12 cases routine work-up was not able to precisely establish a diagnosis of CLL or MZBL, and CLL or MCL. In these cases the presence of JAM-C was considered a strong argument against a GC-origin of the malignant B cells. Addition of JAM-C to antibodies used in the Matutes score increased the sensitivity and specificity of this score for the diagnosis of CLL. Furthermore, it may help differentiating MZBL from LPL which otherwise display overlapping immunophenotypes. Conclusion JAM-C constitutes a new diagnostic marker for the differential diagnosis of B cell lymphomas, and is particularly useful for the distinction between CLL and LPL (negative staining) on the one hand and mantle cell and marginal zone B cell lymphomas (positive staining) on the other hand. Disclosures: No relevant conflicts of interest to declare.