The Lymph Node Niche.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. SCI-51-SCI-51
Author(s):  
Thorsten R. Mempel
Keyword(s):  
Lymph Nodes ◽  
B Lymphocyte ◽  
Immune Cell ◽  
Conflicts Of Interest ◽  
Lymphatic Vessels ◽  
Potential Threat ◽  
Peripheral Tissues ◽  
Pathogen Invasion ◽  
Cognate Antigen

Abstract Abstract SCI-51 Lymph nodes provide specialized stromal environments that support the maintenance and homeostasis of T and B lymphocyte populations and are also staging grounds for lymphocyte effector responses against pathogens and transformed cells. They serve as immune information hotspots by collecting lymph fluid from peripheral tissues, especially our external and internal epithelial body surfaces, thus displaying a condensed representation of foreign and self-antigens at these sites in addition to integrating innate alarm signals that report tissue damage or pathogen invasion. Naïve B and T cells constantly traffic through these environments via the blood stream and efferent lymphatic vessels, which allows for efficient matching of their antigen receptor repertoires with the regional antigenic landscape. Depending on the absence or presence of signs of a potential threat to the organism, the result may be either tolerance or immunity towards the origin of these antigens. The architecture of lymph nodes is optimized to facilitate the presentation of lymph-borne antigen in various forms and to guide naïve lymphocytes in their search for 'their' cognate antigen in the form in which they are able to 'see' it. It also facilitates the cellular crosstalk with other immune cell populations that shape and regulate an ensuing adaptive response if cognate antigen is encountered in an immunogenic context. Our conception of how these various tasks are accomplished has recently been enriched through new methodological approaches that include the dynamic in situ or in vivo visualization of cellular and molecular processes using modern microscopy technology. We will review some recent insights into the function of lymph nodes derived from these studies. Disclosures No relevant conflicts of interest to declare.

Mesenchymal Stem Cells From Patients with Acute Myeloid Leukemia (AML) Can Differentiate Into B-Cells in NOD/SCID/IL-2Rγ-/- Mice.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 4573-4573
Author(s):  
Rui-Yu Wang ◽  
Yue-Xi Shi ◽  
Zhihong Zeng ◽  
Wendy D. Schober ◽  
Teresa J. McQueen ◽  
...  
Keyword(s):  
Stem Cells ◽  
Bone Marrow ◽  
Mesenchymal Stem Cells ◽  
B Lymphocyte ◽  
Conflicts Of Interest ◽  
Lymphoid Cells ◽  
Proliferative Potential ◽  
Unexpected Finding ◽  
Nog Mice

Abstract Abstract 4573 Human mesenchymal stem cells (MSCs) derived from bone marrows are characterized by high proliferative potential and pluripotentiality to differentiate into multiple lineages such as osteo-, chondro-, and adipogenic cells. MSC express CD105, CD73 and CD90, but not CD45, CD34, CD14 or CD11b, CD79alpha or CD19 and HLA-DR surface molecules. In this study, we observed that MSC derived from the bone marrow of four AML patients differentiated into B-cell lymphoblasts with NOD/SCID/IL-2Rg-/- engraftment potential. MSC cell lines were established by culturing adherent cells from newly diagnosed AML (n=4) age 20 to 74 years in alpha-DMEM medium supplement with 20% fetal bovine serum. Surface antigen phenotype analysis and G-banding karyotype analysis were performed in passage 2 to 4. FACS-sorted CD90 positive cells were then intravenously (I.V.) injected into NOD/SCID/IL-2Rg-/- (NOG) mice via tail vein (n=9) or into the bone marrow (n=3). Circulating cells were analyzed for CD19, CD33, CD34, and CD90 expression on day 36, 45, 60, 75 after injection of MSC. Results 1) G-banding showed normal karyotype in all MSC; 2) Injected MSC engrafted and differentiated in NOG mice. Surprisingly, CD19 positive cells were found in all samples starting on day 36 (table) and increased on day 60 and 75 (from d36: 6.9±3.5%, d45:0.7±0.1%, d60:2.6 ± 1.6% and d75: 9.3 ± 1.0%); 3) CD90 positive cells were found on day 45 (range from 0.07-3.96% and decreased to 0.1-0.5% on day 75). Low percentage of CD33 (day 45: 0.19-0.78% and day 60: 0.12-2.53%) and CD34 positive cells (day 45: 0.32-1.9% and day 60: 0.21-2.39%) were observed before day 60 and were undetectable by day 75. Table shows the percentages of CD19+ cells found in circulation in NOD/SCID/IL-2Rg-/- (NOG) mice after MSC I.V. or intra-bone marrow injection. (* Mice died after phlebotomy.) Conclusion Human MSC derived from AML bone marrows have the capacity to differentiate into CD19 positive B lymphocyte in NOG mice in vivo. It has previously been reported that AML can be propagated by a leukemic stem cell with lymphoid characteristics (Cancer Cell 2006, 10, 363-74). Data reported here suggest the possibility that AML-derived MSC give rise to lymphoid cells that engraft in NOG mice. This unexpected finding could shed light on the role of stroma cells in the pathogenesis and propagation of leukemias. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Src-like Adaptor Protein Promotes the CD103+ dendritic Cell Homeostasis in the Lung

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 1339-1339
Author(s):  
Namit Sharma ◽  
Pan Zhongda ◽  
Tracy Lauren Smith ◽  
Savar Kaul ◽  
Emilie Ernoult ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Immune Response ◽  
Immune Cell ◽  
Conflicts Of Interest ◽  
Adaptor Protein ◽  
Cell Receptor ◽  
Apoptotic Cells ◽  
Direct Role

Abstract Dendritic cells (DCs) along with mast cells function as sentinels for the innate immune system and perform as antigen presenting cells (APCs) to mount an adaptive immune response against invading pathogen. FLT3 receptor tyrosine kinase signaling has been shown to regulate the homeostatic mechanisms of subsets of DCs particularly, CD103+DCs compared to CD11b+DCs. CD103+DCs are regarded as APCs with superior capabilities to mount an effective immune response, thus understanding their homeostasis mechanism(s)/function is of paramount importance to devise effective therapeutics including DC vaccines. The Src-like adapter protein (SLAP) has been shown to dampen the signaling downstream of receptor tyrosine kinases including FLT3, cKit, and immune cell receptors including T cell receptor, B cell receptor, and Granulocyte-monocyte colony stimulating factor receptor via by recruiting c-Cbl, an ubiquitin ligase. Here, we report that SLAP deficient mice (KO) have reduced numbers of CD103+DC in lung while equal numbers in liver and kidney compared to control mice. To further confirm reduced CD103+DC in the lung, efferocytosis assays that are dependent upon CD+103 DC in lung epithelium to cleanse the apoptotic cells were performed. Flow cytometric quantification of CD103+DCs that uptake fluorescently labeled apoptotic cells administered via intranasal route and migrate to mediastinal lymph nodes confirmed reduced number of CD103+DCs in SLAP KO mice. Further analysis of DC progenitor populations showed reduced pre-DC progenitor in the lung in SLAP KO mice while bone marrow compartment showed equal progenitor populations including pre-DC and common dendritic progenitors suggesting the role of SLAP in localized FLT3 signaling in the lung. Consistently, DCs in lymphoid compartment including spleen, thymus, inguinal and popliteal lymph node did not show any defects. Upon further dissecting the cellular mechanism, SLAP KO DCs showed increased apoptosis while having similar proliferation potential in vivo at steady state.Bone marrow progenitors from SLAP KO mice failed to generate mature DCs in the presence of FLT3 ligand in vitrodue to enhanced apoptosis at early time points. Also, submaximal inhibition of FLT3 with an inhibitor, quizartinib partially rescues the apoptotic phenotype of SLAP KO bone marrow progenitors suggesting a cell-intrinsic role of SLAP in the survival of DCs. Biochemical analysis revealed that SLAP is directly recruited to the juxta-membrane residues of the FLT3 receptor in an inducible manner suggesting a direct role of SLAP in the regulation of FLT3 signaling. Phosphoflow analysis of DCs generated in the combined presence of GMCSF and FLT3 ligands showed that SLAP promotes the signaling to SHP2 while perturbs signaling to the mTOR pathway. Together these results suggest that SLAP is a critical regulator of CD103+DCs homeostasis in selective peripheral organs including the lung. Disclosures No relevant conflicts of interest to declare.

scholarly journals Dendritic cell entry to lymphatic capillaries is orchestrated by CD44 and the hyaluronan glycocalyx

2021 ◽  
Vol 4 (5) ◽  
pp. e202000908
Author(s):  
Louise A Johnson ◽  
Suneale Banerji ◽  
B Christoffer Lagerholm ◽  
David G Jackson
Keyword(s):  
Lymph Nodes ◽  
Gene Knockout ◽  
Lymphatic Vessels ◽  
Skin Inflammation ◽  
Vital Role ◽  
Cell Entry ◽  
Peripheral Tissues ◽  
Weak Binding ◽  
Endothelial Receptor

DCs play a vital role in immunity by conveying antigens from peripheral tissues to draining lymph nodes, through afferent lymphatic vessels. Critical to the process is initial docking to the lymphatic endothelial receptor LYVE-1 via its ligand hyaluronan on the DC surface. How this relatively weak binding polymer is configured for specific adhesion to LYVE-1, however, is unknown. Here, we show that hyaluronan is anchored and spatially organized into a 400–500 nm dense glycocalyx by the leukocyte receptor CD44. Using gene knockout and by modulating CD44-hyaluronan interactions with monoclonal antibodies in vitro and in a mouse model of oxazolone-induced skin inflammation, we demonstrate that CD44 is required for DC adhesion and transmigration across lymphatic endothelium. In addition, we present evidence that CD44 can dynamically control the density of the hyaluronan glycocalyx, regulating the efficiency of DC trafficking to lymph nodes. Our findings define a previously unrecognized role for CD44 in lymphatic trafficking and highlight the importance of the CD44:HA:LYVE-1 axis in its regulation.

Abstract MP52: Hypertensive Stimuli Indirectly Stimulate Mouse Mesometrial Lymphangiogenesis Through Immune Cells

Hypertension ◽  
2021 ◽  
Vol 78 (Suppl_1) ◽  
Author(s):  
Brooke K Wilcox ◽  
Shobana Navaneethabalakrishnan ◽  
Karina A Martinez ◽  
Anil Pournouri ◽  
Marissa R Henley ◽  
...  
Keyword(s):  
Immune Cell ◽  
Lymphatic Vessels ◽  
Lymphatic Endothelial Cell ◽  
Conditioned Media ◽  
Murine Splenocytes ◽  
Sprout Length ◽  
Lymphatic Density ◽  
Fetal Bovine ◽  
Vascular Beds

We previously reported increased renal lymphatic density in multiple mouse models of hypertension, and further augmenting renal lymphatics lowers blood pressure. However, whether interstitial levels of hypertensive stimuli have a direct effect on lymphatics or an indirect effect through secreted immune cell factors has not been examined. We hypothesized that hypertensive stimuli directly increases lymphatic endothelial cell (LEC) proliferation and increases sprouting of mouse mesometrial lymphatic vessels. Murine LECs were cultured and treated with angiotensin II (angII), salt, and asymmetric dimethylarginine (ADMA) for 24 hours. To mimic the in vivo environment, a lymphatic-specific reporter mouse (Prox1-tdTomato) mesometrium tissue explant was treated with either the same hypertensive stimuli or with hypertensive conditioned media for 8 days. Mesometrial vascular beds were cultured in DMEM supplemented with 20% fetal bovine serum to induce lymphatic sprouting and this was replenished every day. The conditioned media was made by treating murine splenocytes for 24 hours with the same hypertensive stimuli. These stimuli had no effect on murine LEC proliferation. Hypertensive stimuli significantly decreased mesometrial lymphatic vessel sprout length (SL) and sprout number (SN) compared to controls (control SL in pixels by ImageJ analysis: 34.0 ± 2.6, angII: 3.7 ± 2.6, salt: 2.67 ± 2.18, ADMA: 9.06 ± 5.12, all p<0.05; control SN: 7 ± 3, angII: 0 ± 0, salt: 0 ± 0, ADMA: 1 ± 1, all p<0.05). Conditioned media treatment normalized SL and SN by day 8 for all hypertensive stimuli except salt. In conclusion, hypertensive stimuli directly inhibit mesometrial lymphangiogenesis, but this was mitigated by hypertensive stimuli induced immune cell secreted factors.

scholarly journals Neutrophils rapidly migrate via lymphatics after Mycobacterium bovis BCG intradermal vaccination and shuttle live bacilli to the draining lymph nodes

Blood ◽  
2005 ◽  
Vol 106 (5) ◽  
pp. 1843-1850 ◽  
Author(s):  
Valérie Abadie ◽  
Edgar Badell ◽  
Patrice Douillard ◽  
Danielle Ensergueix ◽  
Pieter J. M. Leenen ◽  
...  
Keyword(s):  
Lymph Nodes ◽  
Mycobacterium Bovis ◽  
Lymphatic Vessels ◽  
Lymphoid Organ ◽  
Host Cells ◽  
Intradermal Vaccination ◽  
Bcg Vaccination ◽  
Inflammatory Monocytes ◽  
Draining Lymph Nodes

Abstract The early innate response after Mycobacterium bovis bacille Calmette-Guérin (BCG) vaccination is poorly characterized but probably decisive for subsequent protective immunity against tuberculosis. Therefore, we vaccinated mice with fluorescent BCG strains in the ear dorsum, as a surrogate of intradermal vaccination in humans. During the first 3 days, we tracked BCG host cells migrating out of the dermis to the auricular draining lymph nodes (ADLNs). Resident skin dendritic cells (DCs) or macrophages did not play a predominant role in early BCG capture and transport to ADLNs. The main BCG host cells rapidly recruited both in the dermis and ADLNs were neutrophils. Fluorescent green or red BCG strains injected into nonoverlapping sites were essentially sheltered by distinct neutrophils in the ADLN capsule, indicating that neutrophils had captured bacilli in peripheral tissue and transported them to the lymphoid organ. Strikingly, we observed BCG-infected neutrophils in the lumen of lymphatic vessels by confocal microscopy on ear dermis. Fluorescence-labeled neutrophils injected into the ears accumulated exclusively into the ipsilateral ADLN capsule after BCG vaccination. Thus, we provide in vivo evidence that neutrophils, like DCs or inflammatory monocytes, migrate via afferent lymphatics to lymphoid tissue and can shuttle live microorganisms. (Blood. 2005;106: 1843-1850)

Transgenic overexpression of human IL-17E results in eosinophilia, B-lymphocyte hyperplasia, and altered antibody production

Blood ◽  
2002 ◽  
Vol 100 (7) ◽  
pp. 2330-2340 ◽  
Author(s):  
Mee Rhan Kim ◽  
Raffi Manoukian ◽  
Richard Yeh ◽  
Scott M. Silbiger ◽  
Dimitry M. Danilenko ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Transgenic Mice ◽  
Lymph Nodes ◽  
Peripheral Blood ◽  
B Lymphocyte ◽  
Fold Increase ◽  
High Serum ◽  
Interleukin 17 ◽  
Immune Functions

We have identified and cloned a novel human cytokine with homology to cytokines of the interleukin-17 (IL-17) family, which we have termed human IL-17E (hIL-17E). With the identification of several IL-17 family members, it is critical to understand the in vivo function of these molecules. We have generated transgenic mice overexpressing hIL-17E using an apolipoprotein E (ApoE) hepatic promoter. These mice displayed changes in the peripheral blood, particularly, a 3-fold increase in total leukocytes consisting of increases in eosinophils, lymphocytes, and neutrophils. Splenomegaly and lymphoadenopathy were predominant and included marked eosinophil infiltrates and lymphoid hyperplasia. CCR3+ eosinophils increased in the blood and lymph nodes of the transgenic mice by 50- and 300-fold, respectively. Eosinophils also increased 8- to 18-fold in the bone marrow and spleen, respectively. In the bone marrow, most of the eosinophils had an immature appearance. CD19+ B cells increased 2- to 5-fold in the peripheral blood, 2-fold in the spleen, and 10-fold in the lymph nodes of transgenic mice, whereas CD4+ T lymphocytes increased 2-fold in both blood and spleen. High serum levels of the cytokines IL-2, IL-4, IL-5, granulocyte colony-stimulating factor, eotaxin, and interferon γ were observed. Consistent with B-lymphocyte increases, serum immunoglobulin (Ig) M, IgG, and IgE were significantly elevated. Antigenic challenge of the transgenic mice with keyhole limpet hemocyanin (KLH) resulted in a decrease in anti-KLH IgG accompanied by increases of anti-KLH IgA and IgE. In situ hybridization of transgenic tissues revealed that IL-17Rh1 (IL-17BR/Evi27), a receptor that binds IL-17E, is up-regulated. Taken together, these data indicate that IL-17E regulates hematopoietic and immune functions, stimulating the development of eosinophils and B lymphocytes. The fact that hIL-17E overexpression results in high levels of circulating eosinophils, IL-4, IL-5, eotaxin, and IgE suggests that IL-17E may be a proinflammatory cytokine favoring Th2-type immune responses.

scholarly journals Dense poly(ethylene glycol) coatings maximize nanoparticle transport across lymphatic endothelial cells

2020 ◽  
Author(s):  
Jacob McCright ◽  
Colin Skeen ◽  
Jenny Yarmovsky ◽  
Katharina Maisel
Keyword(s):  
Endothelial Cells ◽  
Ethylene Glycol ◽  
Lymph Nodes ◽  
Lymphatic Vessels ◽  
Lymphatic Endothelial Cells ◽  
Poly Ethylene Glycol ◽  
Nanoparticle Transport ◽  
Peripheral Tissues ◽  
Transport Efficiency ◽  
Poly Ethylene

AbstractLymphatic vessels have received considerable attention in recent years as delivery route for immune modulatory therapies to the lymph nodes. Lymph node targeting of immunotherapies and vaccines has been shown to significantly enhance their therapeutic efficacy. Lymphatics transport functions materials from peripheral tissues to the lymph nodes, including small 10 – 250 nm therapeutic nanoparticles. While size required to enter lymphatic vessels, surface chemistry is more poorly studied. Here, we probed the effects of surface poly(ethylene glycol) (PEG) density on nanoparticle transport across lymphatic endothelial cells (LECs). We differentially PEGylated model carboxylate-modified polystyrene nanoparticles to form either a brush or dense brush PEG conformation on the nanoparticle surfaces. Using an established in-vitro lymphatic transport model, we found that the addition of any PEG improved the transport of nanoparticles through lymphatic endothelial cells (2.5 - 2.6 ± 0.9% transport efficiency at 24 hours) compared to the unmodified PS-COOH nanoparticles (0.05 ± 0.05% transport efficiency at 24 hours). Additionally, we found that transcellular transport is maximized (4.2 ± 0.7% transport efficiency at 24 hours) when the PEG is in a dense brush conformation on nanoparticle surfaces, corresponding with a high grafting density (Rf/D = 4.9). These results suggest that PEG conformation has a crucial role in determining translocation of nanoparticles across LECs and into lymphatic vessels. Thus, we identified PEG density as a major design criteria for maximizing lymphatic targeting of therapeutic nanoparticle formulations that can be widely applied to enhance immunotherapeutic and vaccine outcomes in future studies.

scholarly journals Ex vivo Demonstration of Functional Deficiencies in Popliteal Lymphatic Vessels from TNF-Tg Mice with Inflammatory Arthritis

2020 ◽  
Author(s):  
Joshua P. Scallan ◽  
Echoe M. Bouta ◽  
Homaira Rahimi ◽  
H. Mark Kenney ◽  
Christopher T. Ritchlin ◽  
...  
Keyword(s):  
Lymph Nodes ◽  
Repeated Measures ◽  
Inflammatory Arthritis ◽  
Ex Vivo ◽  
Lymphatic Vessels ◽  
Chronic Inflammatory Arthritis ◽  
Wide Range ◽  
Nos Inhibitors ◽  
Draining Lymph Nodes

AbstractBackgroundRheumatoid arthritis (RA) is a progressive immune-mediated inflammatory disease characterized by intermittent episodes of pain and inflammation in affected joints, or flares. Recent studies demonstrated lymphangiogenesis and expansion of draining lymph nodes during chronic inflammatory arthritis, and lymphatic dysfunction associated with collapse of draining lymph nodes in RA patients and TNF-transgenic (TNF-Tg) mice experiencing arthritic flare. As the intrinsic differences between lymphatic vessels afferent to healthy, expanding, and collapsed draining lymph nodes are unknown, we characterized the ex vivo behavior of popliteal lymphatic vessels (PLVs) from WT and TNF-Tg mice. We also interrogated the mechanisms of lymphatic dysfunction through inhibition of nitric oxide synthase (NOS).MethodsPopliteal lymph nodes (PLNs) in TNF-Tg mice were phenotyped as Expanding or Collapsed by in vivo ultrasound and age-matched to WT littermate controls. The PLVs were harvested and cannulated for ex vivo functional analysis over a relatively wide range of hydrostatic pressures (0.5 to 10 cmH2O) to quantify the end diastolic diameter (EDD), tone, amplitude (AMP), ejection fraction (EF), contraction frequency (FREQ) and fractional pump flow (FPF) with or without NOS inhibitors Data was analyzed using repeated measures two-way ANOVA with Bonferroni’s post hoc test.ResultsReal time videos of the cannulated PLVs demonstrated the predicted phenotypes of robust versus weak contractions of the WT versus TNF-Tg PLV, respectively. Quantitative analyses confirmed that TNF-Tg PLVs had significantly decreased AMP, EF and FPF versus WT (p<0.05). EF and FPF were recovered by NOS inhibition, while the reduction in AMP was NOS independent. No differences in EDD, tone, or FREQ were observed between WT and TNF-Tg PLVs, nor between Expanding versus Collapsed PLVs.ConclusionThese findings support the concept that chronic inflammatory arthritis leads to NOS dependent and independent draining lymphatic vessel dysfunction that exacerbates disease, and may trigger arthritic flare due to decreased egress of inflammatory cells and soluble factors from affected joints.

scholarly journals TLR-9 and IL-15-Driven Clonal Expansion of B-CLL Cells

Blood ◽  
2014 ◽  
Vol 124 (21) ◽  
pp. 1937-1937
Author(s):  
Patricia K. A. Mongini ◽  
Rashmi Gupta ◽  
Charles C. Chu ◽  
Joanna Stein ◽  
Tatjana Stankovic ◽  
...  
Keyword(s):  
Bone Marrow ◽  
Cell Growth ◽  
Lymph Nodes ◽  
Conflicts Of Interest ◽  
Leukemic Cell ◽  
Clonal Expansion ◽  
Lymphocytic Leukemia ◽  
Clinical Progression

Abstract Clinical progression of B cell chronic lymphocytic leukemia (B-CLL) is linked to clonal growth within pseudo-follicles, typically within lymph nodes, bone marrow and spleen, and occasionally lungs and skin. Both the clone’s antigen receptor and stromal milieu appear to influence its growth rate. An involvement of TLR signals seems probable based on atypically elevated TLR-9 expression within B-CLL cells and the likelihood that the specificity of B-CLL antigen receptors (BCR) facilitates the internalization of molecules from apoptotic cells and/or microbes that are physically linked to CpG DNA. Nevertheless, recent findings that a large subset of B-CLL undergoes in vitro apoptosis upon stimulation with CpG-rich oligodeoxynucleotides (ODN) raised questions about a central role for TLR-9 signaling. Using a CFSE-based model for examining in vitro B-CLL clonal expansion/viability and a cohort consisting of 19 IGHV mutated (M) and 19 unmutated (U) B-CLL, we report that TLR-9 signaling is uniformly stimulatory when accompanied by signals from IL-15. Importantly, this cytokine is known to be constitutively produced by stromal cells in normal bone marrow, lymph nodes, and spleen and in a constitutive/inducible manner within skin and lungs. We show that B-CLL display reproducible inter-clonal differences in the number of division cycles attained and/or lymphoblast survival that were not linked to IGHV mutation status, but were statistically linked to whether the patient leukemic population contained subclones with trisomy-12 (p=0.0003) or contained subclones with both an ATM anomaly (11q22 del and/or ATM mutation) and 13q14 del (p=0.009). When all B-CLL clones were assessed, in vitro high-division or high-viability status in response to ODN + IL-15 was not statistically linked to clinical progression as determined by time to first treatment (TFT). Nonetheless, in vitro high-division status showed a statistically-significant direct linkage to patient survival (OS) (p=0.019 for OS within B-CLL manifesting > 50% cells with > 2 divisions versus B-CLL with < 50% cells with > 2 divisions). Subdivision of the total cohort into U-CLL and M-CLL subsets revealed that the link of high division status with overall survival is most characteristic of U-CLL. Immunohistological evidence of IL-15-producing cells within or proximal to Ki-67-positive pseudo-follicles in B-CLL-infiltrated spleen is consistent with a role for ODN + IL-15 signaling in promoting in vivo leukemic cell growth. Taken together, the findings from this study support the concept that in vivo B-CLL clonal expansion is dependent upon leukemic B-CLL homing to tissue sites where IL-15 is typically sequestered along with intrinsic properties of the B-CLL clone, e.g. cytogenetic anomalies within members of a B-CLL clone that heighten leukemic cell growth and/or survival and an expression of U-BCRs specific for apoptotic cell debris that increase the opportunity for TLR-9 signaling. Disclosures No relevant conflicts of interest to declare.

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