Disruption of CD47-SIRPα signaling restores inflammatory function in tumor-associated myeloid-derived suppressor cells

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous immune population with diverse immunosuppressive functions in solid tumors. Here, we explored the role of the tumor microenvironment in regulating MDSC differentiation and immunosuppressive properties via signal-regulatory protein alpha (SIRPα)/CD47 signaling. In a murine melanoma model, we observed progressive increases in monocytic MDSCs and monocyte-derived dendritic cells that exhibited potent T cell-suppressive capabilities. These adaptations could be recapitulated in vitro by exposing hematopoietic stem cells to tumor-derived factors. Engagement of CD47 with SIRPα on myeloid cells reduced their phagocytic capability, enhanced expression of immune checkpoints, increased reactive oxygen species production, and suppressed T cell proliferation. Perturbation of SIRPα signaling restored phagocytosis and antigen presentation by MDSCs, which was accompanied by renewed T cell activity and delayed tumor growth in multiple solid cancers. These data highlight that therapeutically targeting myeloid functions in combination with immune checkpoint inhibitors could enhance anti-tumor immunity.

Modelling Structural Elements and Functional Responses to Lymphatic-Delivered Cues in a Murine Lymph Node on a Chip

Lymph nodes (LNs) are organs of the immune system, critical for maintenance of homeostasis and initiation of immune responses, yet there are few models that accurately recapitulate LN functions in vitro. To tackle this issue, an engineered murine LN (eLN) was developed, replicating key cellular components of the mouse LN; incorporating primary murine lymphocytes, fibroblastic reticular cells (FRCs), and lymphatic endothelial cells (LECs). T and B cells compartments are incorporated within the eLN that mimic LN cortex and paracortex architectures. When challenged, the eLN elicits both robust inflammatory responses and antigen-specific immune activation, showing that the system can differentiate between non-specific and antigen-specific responses and can be monitored in real-time. Beyond immune responses, this model also enables interrogation of changes in stromal cells, thus permitting investigations of all LN cellular components in homeostasis and different disease settings, such as cancer. Here, we present how LN behavior can be influenced by murine melanoma-derived factors. In conclusion, the eLN model presents a promising platform for in vitro study of LN biology that will enhance understanding of stromal and immune responses in the murine LN, and in doing so will enable development of novel therapeutic strategies to improve LN responses in disease. This article is protected by copyright. All rights reserved.

Single-cell RNA sequencing unifies developmental programs of Esophageal and Gastric Intestinal Metaplasia

Intestinal metaplasia in the esophagus (Barrett's Esophagus BE-IM) and stomach (GIM) are considered precursors for esophageal and gastric adenocarcinoma, respectively. We hypothesize that BE-IM and GIM follow parallel developmental trajectories in response to differing inflammatory insults. Here, we construct a single-cell RNA-seq atlas, supported by protein expression studies, of the entire gastrointestinal tract spanning physiologically normal and pathological states including gastric metaplasia in the esophagus (E-GM), BE-IM, atrophic gastritis, and GIM. We demonstrate that BE-IM and GIM share molecular features, and individual cells simultaneously possess transcriptional properties of gastric and intestinal epithelia, suggesting phenotypic mosaicism. Transcriptionally E-GM resembles atrophic gastritis; genetically, it is clonal and has a lower mutational burden than BE-IM. Finally, we show that GIM and BE-IM acquire a pro-tumorigenic, activated fibroblast microenvironment. These findings suggest that BE-IM and GIM can be considered molecularly similar entities in adjacent organs, opening the path for shared detection and treatment strategies.

Deployable extrusion bioprinting of compartmental tumoroids with cancer associated fibroblasts for immune cell interactions

Realizing the translational impacts of three-dimensional (3D) bioprinting for cancer research necessitates innovation in bioprinting workflows which integrate affordability, user-friendliness, and biological relevance. Herein, we demonstrate 'BioArm', a simple, yet highly effective extrusion bioprinting platform, which can be folded into a carry-on pack, and rapidly deployed between bio-facilities. BioArm enabled the reconstruction of compartmental tumoroids with cancer-associated fibroblasts (CAFs), forming the shell of each tumoroid. The 3D printed core-shell tumoroids showedde novosynthesized extracellular matrices, and enhanced cellular proliferation compared to the tumour alone 3D printed spheroid culture. Further, thein vivophenotypes of CAFs normally lost after conventional 2D co-culture re-emerged in the bioprinted model. Embedding the 3D printed tumoroids in an immune cell-laden collagen matrix permitted tracking of the interaction between immune cells and tumoroids, and subsequent simulated immunotherapy treatments. Our deployable extrusion bioprinting workflow could significantly widen the accessibility of 3D bioprinting for replicating multi-compartmental architectures of tumour microenvironment, and for developing strategies in cancer drug testing in the future.

Identification of aceNKPs, a committed common progenitor population of the ILC1 and NK cell continuum

The development of innate lymphoid cell (ILC) transcription factor reporter mice has shown a previously unexpected complexity in ILC hematopoiesis. Using novel polychromic mice to achieve higher phenotypic resolution, we have characterized bone marrow progenitors that are committed to the group 1 ILC lineage. These common ILC1/NK cell progenitors (ILC1/NKP), which we call "aceNKPs", are defined as lineage-Id2+IL-7Rα+CD25-α4β7-NKG2A/C/E+Bcl11b-. In vitro, aceNKPs differentiate into group 1 ILCs, including NK-like cells that express Eomes without the requirement for IL-15, and produce IFN-γ and perforin upon IL-15 stimulation. Following reconstitution of Rag2-/-Il2rg-/- hosts, aceNKPs give rise to a spectrum of mature ILC1/NK cells (regardless of their tissue location) that cannot be clearly segregated into the traditional ILC1 and NK subsets, suggesting that group 1 ILCs constitute a dynamic continuum of ILCs that can develop from a common progenitor. In addition, aceNKP-derived ILC1/NK cells effectively ameliorate tumor burden in a model of lung metastasis, where they acquired a cytotoxic NK cell phenotype. Our results identify the primary ILC1/NK progenitor that lacks ILC2 or ILC3 potential and is strictly committed to ILC1/NK cell production irrespective of tissue homing.

Tumor-Derived Lactic Acid Modulates Activation and Metabolic Status of Draining Lymph Node Stroma

Communication between tumors and the stroma of tumor-draining lymph nodes (TDLN) exists before metastasis arises, altering the structure and function of the TDLN niche. Transcriptional profiling of fibroblastic reticular cells (FRC), the dominant stromal population of lymph nodes, has revealed that FRCs in TDLNs are reprogrammed. However, the tumor-derived factors driving the changes in FRCs remain to be identified. Taking an unbiased approach, we have shown herein that lactic acid (LA), a metabolite released by cancer cells, was not only secreted by B16.F10 and 4T1 tumors in high amounts, but also that it was enriched in TDLNs. LA supported an upregulation of Podoplanin (Pdpn) and Thy1 and downregulation of IL7 in FRCs of TDLNs, making them akin to activated fibroblasts found at the primary tumor site. Furthermore, we found that tumor-derived LA altered mitochondrial function of FRCs in TDLNs. Thus, our results demonstrate a mechanism by which a tumor-derived metabolite connected with a low pH environment modulates the function of fibroblasts in TDLNs. How lymph node function is perturbed to support cancer metastases remains unclear. The authors show that tumor-derived LA drains to lymph nodes where it modulates the function of lymph node stromal cells, prior to metastatic colonization.

Microenvironmental modulation of the developing tumour: an immune-stromal dialogue

Successful establishment of a tumour relies on a cascade of interactions between cancer cells and stromal cells within an evolving microenvironment. Both immune and nonimmune cellular components are key factors in this process, and the individual players may change their role from tumour elimination to tumour promotion as the microenvironment develops. While the tumour-stroma crosstalk present in an established tumour is well-studied, aspects in the early tumour or premalignant microenvironment have received less attention. This is in part due to the challenges in studying this process in the clinic or in mouse models. Here, we review the key anti- and pro-tumour factors in the early microenvironment and discuss how understanding this process may be exploited in the clinic.

Stromal-driven and Amyloid β-dependent induction of neutrophil extracellular traps modulates tumor growth

Tumors consist of cancer cells and a network of non-cancerous stroma. Cancer-associated fibroblasts (CAF) are known to support tumorigenesis, and are emerging as immune modulators. Neutrophils release histone-bound nuclear DNA and cytotoxic granules as extracellular traps (NET). Here we show that CAFs induce NET formation within the tumor and systemically in the blood and bone marrow. These tumor-induced NETs (t-NETs) are driven by a ROS-mediated pathway dependent on CAF-derived Amyloid β, a peptide implicated in both neurodegenerative and inflammatory disorders. Inhibition of NETosis in murine tumors skews neutrophils to an anti-tumor phenotype, preventing tumor growth; reciprocally, t-NETs enhance CAF activation. Mirroring observations in mice, CAFs are detected juxtaposed to NETs in human melanoma and pancreatic adenocarcinoma, and show elevated amyloid and β-Secretase expression which correlates with poor prognosis. In summary, we report that CAFs drive NETosis to support cancer progression, identifying Amyloid β as the protagonist and potential therapeutic target.

ILC2-driven innate immune checkpoint mechanism antagonizes NK cell antimetastatic function in the lung

Metastasis constitutes the primary cause of cancer-related deaths, with the lung being a commonly affected organ. We found that activation of lung-resident group 2 innate lymphoid cells (ILC2s) orchestrated suppression of natural killer (NK) cell-mediated innate antitumor immunity, leading to increased lung metastases and mortality. Using multiple models of lung metastasis, we show that interleukin (IL)-33-dependent ILC2 activation in the lung is involved centrally in promoting tumor burden. ILC2-driven innate type 2 inflammation is accompanied by profound local suppression of interferon-γ production and cytotoxic function of lung NK cells. ILC2-dependent suppression of NK cells is elaborated via an innate regulatory mechanism, which is reliant on IL-5-induced lung eosinophilia, ultimately limiting the metabolic fitness of NK cells. Therapeutic targeting of IL-33 or IL-5 reversed NK cell suppression and alleviated cancer burden. Thus, we reveal an important function of IL-33 and ILC2s in promoting tumor metastasis via their capacity to suppress innate type 1 immunity.

Stromal regulation of tumor-associated lymphatics

Recent advances have identified a growing array of roles played by lymphatics in the tumor microenvironment, from providing a route of metastasis to immune modulation. The tumor microenvironment represents an exceptionally complex, dynamic niche comprised of a diverse mixture of cancer cells and normal host cells termed the stroma. This review discusses our current understanding of stromal elements and how they regulate lymphatic growth and functional properties in the tumor context.

Tumors induce de novo steroid biosynthesis in T cells to evade immunity

Tumors subvert immune cell function to evade immune responses, yet the complex mechanisms driving immune evasion remain poorly understood. Here we show that tumors induce de novo steroidogenesis in T lymphocytes to evade anti-tumor immunity. Using a transgenic steroidogenesis-reporter mouse line we identify and characterize de novo steroidogenic immune cells, defining the global gene expression identity of these steroid-producing immune cells and gene regulatory networks by using single-cell transcriptomics. Genetic ablation of T cell steroidogenesis restricts primary tumor growth and metastatic dissemination in mouse models. Steroidogenic T cells dysregulate anti-tumor immunity, and inhibition of the steroidogenesis pathway is sufficient to restore anti-tumor immunity. This study demonstrates T cell de novo steroidogenesis as a mechanism of anti-tumor immunosuppression and a potential druggable target.

Single-Cell RNA Sequencing Reveals a Dynamic Stromal Niche That Supports Tumor Growth

Here, using single-cell RNA sequencing, we examine the stromal compartment in murine melanoma and draining lymph nodes (LNs) at points across tumor development, providing data at http://www.teichlab.org/data/. Naive lymphocytes from LNs undergo activation and clonal expansion within the tumor, before PD1 and Lag3 expression, while tumor-associated myeloid cells promote the formation of a suppressive niche. We identify three temporally distinct stromal populations displaying unique functional signatures, conserved across mouse and human tumors. Whereas "immune" stromal cells are observed in early tumors, "contractile" cells become more prevalent at later time points. Complement component C3 is specifically expressed in the immune population. Its cleavage product C3a supports the recruitment of C3aR+ macrophages, and perturbation of C3a and C3aR disrupts immune infiltration, slowing tumor growth. Our results highlight the power of scRNA-seq to identify complex interplays and increase stromal diversity as a tumor develops, revealing that stromal cells acquire the capacity to modulate immune landscapes from early disease.

Characterization of microsporidian Ameson herrnkindi sp. nov. infecting Caribbean spiny lobsters Panulirus argus

The Caribbean spiny lobster Panulirus argus supports a large and valuable fishery in the Caribbean Sea. In 2007-2008, a rare microsporidian parasite with spore characteristics typical of the Ameson genus was detected in 2 spiny lobsters from southeast Florida (FL). However, the parasite species was not confirmed by molecular analyses. To address this deficiency, reported here are structural and molecular data on single lobsters displaying comparable 'cotton-like' abdominal muscle containing ovoid microsporidian spores found at different locations in FL in 2014 and 2018 and in Saint Kitts and Nevis Islands in 2017. In the lobster from 2014, multiple life stages consistent with an Ameson-like monokaryotic microsporidian were detected by transmission electron microscopy. A partial (1228 bp) small subunit (SSU) rRNA gene sequence showed each microsporidia to be identical and positioned it closest phylogenetically to Ameson pulvis in a highly supported clade also containing A. michaelis, A. metacarcini, A. portunus, and Nadelspora canceri. Using ecological, pathological, ultrastructural, and molecular data, the P. argus microsporidian has been assigned to a distinct species: Ameson herrnkindi.

Parasitic dinoflagellate Hematodinium perezi prevalence in larval and juvenile blue crabs Callinectes sapidus from coastal bays of Virginia

The parasitic dinoflagellate Hematodinium perezi infects the American blue crab Callinectes sapidus and other decapods along the Eastern seaboard and Gulf of Mexico coast of the USA. Large juvenile and adult blue crabs experience high mortality during seasonal outbreaks of H. perezi, but less is known about its presence in the early life history stages of this host. We determined the prevalence of H. perezi in megalopae and early benthic juvenile crabs from multiple locations along the Virginia portion of the Delmarva Peninsula. The DNA of H. perezi was not detected in any megalopae collected from several locations within the oceanic coastal bay complex in which H. perezi is found at high prevalence levels. However, prevalence levels were high in early benthic juveniles from 2 oceanic coastal embayments: South Bay and Cobb Bay. Prevalence levels were lower at locations within Chesapeake Bay, including Cherrystone Creek, Hungars Creek, and Pungoteague Creek. Sampling over different seasons and several consecutive years indicates that disease transmission occurs rapidly after megalopae settle in high-salinity bays along the Delmarva Peninsula during the late summer and fall. Infected juvenile crabs can overwinter with the parasite and, when subjected to increasing water temperatures in spring, infections progress rapidly, culminating in transmission to other crabs in late spring and early summer. In high-salinity embayments, H. perezi can reach high prevalence levels and may significantly affect recruitment of juvenile blue crabs into the adult fishery.

Impact of Locally Administered Carboxydextran-Coated Super-Paramagnetic Iron Nanoparticles on Cellular Immune Function

Interstitially administered iron oxide particles are currently used for interoperative localization of sentinel lymph nodes (LNs) in cancer staging. Several studies have described concerns regarding the cellular accumulation of iron oxide nanoparticles relating them to phenotype and function deregulation of macrophages, impairing their ability to mount an appropriate immune response once an insult is present. This study aims to address what phenotypic and functional changes occur during lymphatic transit and accumulation of these particles. Data show that 60 nm carboxydextran-coated iron nanoparticles use a noncellular mechanism to reach the draining LNs and that their accumulation in macrophages induces transient phenotypic and functional changes. Nevertheless, macrophages recover their baseline levels of response within 7 days, and are still able to mount an appropriate response to bacterially induced inflammation.

Macrophages are exploited from an innate wound healing response to facilitate cancer metastasis

Tumour-associated macrophages (TAMs) play an important role in tumour progression, which is facilitated by their ability to respond to environmental cues. Here we report, using murine models of breast cancer, that TAMs expressing fibroblast activation protein alpha (FAP) and haem oxygenase-1 (HO-1), which are also found in human breast cancer, represent a macrophage phenotype similar to that observed during the wound healing response. Importantly, the expression of a wound-like cytokine response within the tumour is clinically associated with poor prognosis in a variety of cancers. We show that co-expression of FAP and HO-1 in macrophages results from an innate early regenerative response driven by IL-6, which both directly regulates HO-1 expression and licenses FAP expression in a skin-like collagen-rich environment. We show that tumours can exploit this response to facilitate transendothelial migration and metastatic spread of the disease, which can be pharmacologically targeted using a clinically relevant HO-1 inhibitor.

Cancer-associated fibroblasts induce antigen-specific deletion of CD8 + T Cells to protect tumour cells

Tumours have developed strategies to interfere with most steps required for anti-tumour immune responses. Although many populations contribute to anti-tumour responses, tumour-infiltrating cytotoxic T cells dominate, hence, many suppressive strategies act to inhibit these. Tumour-associated T cells are frequently restricted to stromal zones rather than tumour islands, raising the possibility that the tumour microenvironment, where crosstalk between malignant and "normal" stromal cells exists, may be critical for T cell suppression. We provide evidence of direct interactions between stroma and T cells driving suppression, showing that cancer-associated fibroblasts (CAFs) sample, process and cross-present antigen, killing CD8+ T cells in an antigen-specific, antigen-dependent manner via PD-L2 and FASL. Inhibitory ligand expression is observed in CAFs from human tumours, and neutralisation of PD-L2 or FASL reactivates T cell cytotoxic capacity in vitro and in vivo. Thus, CAFs support T cell suppression within the tumour microenvironment by a mechanism dependent on immune checkpoint activation.

Abstract 298: Tumor-associated lymphatic vessels: Hijacking mechanisms of peripheral tolerance

Lymphatic vessels drain fluid, antigens, and immune cells from the periphery to the lymph nodes (LNs). In addition to transporting activated dendritic cells to mount adaptive immune responses in the LN, lymphatic drainage is brings soluble antigens from the periphery to LN-resident immature dendritic cells and B cells. It is also the most common site for cancer metastasis. Despite its importance, the role of tumor-associated lymphatic vessels and their drainage to the LN in regulating host immune responses to the tumor is poorly understood. We show that tumor expression of VEGF-C, the most potent lymphatic growth factor, promotes pro-tumor immune tolerance by several mechanisms. For one, it enhances drainage to the draining LN, where tumor antigens along with suppressive cytokines bathe the LN and could affect B and T cell education there. Second, tumor VEGF-C upregulates CCL21 in the tumor stroma and surrounding lymphatic vessels, which itself promotes T cell infiltration and suppression. Third, VEGF-C drives peritumoral and LN lymphangiogenesis, which can modulate the myeloid cell repertoire towards more suppressive phenotypes. These changes resulted in increased infiltrations of regulatory T cells and myeloid-derived suppressor cells, and increased levels of regulatory cytokines. Interestingly, VEGF-C-expressing tumors were impervious to prior immunization against tumor antigen, unlike control-transfected tumors, which were hindered by the vaccine-induced immune response. Together, these findings suggest that lymphatic drainage serves to maintain peripheral tolerance and that tumors may hijack such mechanisms to escape host immunity.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 298. doi:1538-7445.AM2012-298

Disease will limit future food supply from the global crustacean fishery and aquaculture sectors

Seafood is a highly traded food commodity. Farmed and captured crustaceans contribute a significant proportion with annual production exceeding 10 M metric tonnes with first sale value of $40bn. The sector is dominated by farmed tropical marine shrimp, the fastest growing sector of the global aquaculture industry. It is significant in supporting rural livelihoods and alleviating poverty in producing nations within Asia and Latin America while forming an increasing contribution to aquatic food supply in more developed countries. Nations with marine borders often also support important marine fisheries for crustaceans that are regionally traded as live animals and commodity products. A general separation of net producing and net consuming nations for crustacean seafood has created a truly globalised food industry. Projections for increasing global demand for seafood in the face of level or declining fisheries requires continued expansion and intensification of aquaculture while ensuring best utilisation of captured stocks. Furthermore, continued pressure from consuming nations to ensure safe products for human consumption are being augmented by additional legislative requirements for animals (and their products) to be of low disease status. As a consequence, increasing emphasis is being placed on enforcement of regulations and better governance of the sector; currently this is a challenge in light of a fragmented industry and less stringent regulations associated with animal disease within producer nations. Current estimates predict that up to 40% of tropical shrimp production (>$3bn) is lost annually, mainly due to viral pathogens for which standard preventative measures (e.g. such as vaccination) are not feasible. In light of this problem, new approaches are urgently required to enhance yield by improving broodstock and larval sourcing, promoting best management practices by farmer outreach and supporting cutting-edge research that aims to harness the natural abilities of invertebrates to mitigate assault from pathogens (e.g. the use of RNA interference therapeutics). In terms of fisheries losses associated with disease, key issues are centred on mortality and quality degradation in the post-capture phase, largely due to poor grading and handling by fishers and the industry chain. Occurrence of disease in wild crustaceans is also widely reported, with some indications that climatic changes may be increasing susceptibility to important pathogens (e.g. the parasite Hematodinium). However, despite improvements in field and laboratory diagnostics, defining population-level effects of disease in these fisheries remains elusive. Coordination of disease specialists with fisheries scientists will be required to understand current and future impacts of existing and emergent diseases on wild stocks. Overall, the increasing demand for crustacean seafood in light of these issues signals a clear warning for the future sustainability of this global industry. The linking together of global experts in the culture, capture and trading of crustaceans with pathologists, epidemiologists, ecologists, therapeutics specialists and policy makers in the field of food security will allow these issues to be better identified and addressed.

Lymphatics: at the interface of immunity, tolerance, and tumor metastasis

The lymphatic system has long been accepted as a passive escape route for metastasizing tumor cells. The classic view that lymphatics solely regulate fluid balance, lipid metabolism, and immune cell trafficking to the LN is now being challenged. Research in the field is entering a new phase with increasing evidence suggesting that lymphatics play an active role modulating inflammation, autoimmune disease, and the anti-tumor immune response. Evidence exists to suggest that the lymphatics and chemokines guide LN bi-functionally, driving immunity vs. tolerance according to demand. At sites of chronic inflammation, autoimmunity, and tumors, however, the same chemokines and aberrant lymphangiogenesis foster disease progression. These caveats point to the existence of a complex, finely balanced relationship between lymphatics and the immune system in health and disease. This review discusses emerging concepts in the fields of immunology, tumor biology, and lymphatic physiology, identifying critical, overlapping functions of lymphatics, the LN and lymphoid factors in tipping the balance of immunity vs. tolerance in favor of a growing tumor.

Diseases of spiny lobsters: a review

Spiny lobsters have few reported pathogens, parasites and symbionts. However, they do have a diverse fauna comprised of a pathogenic virus, several bacteria, protozoans, helminths and even symbiotic crustaceans. A few idiopathic syndromes have also been reported, but these appear correlated with lobsters held in poor conditions. Fungal and bacterial pathogens present significant threats for rearing spiny lobsters in aquaculture settings, but only one pathogen, Panulirus argus virus 1, is thought to have damaged a fishery for a spiny lobster. No doubt others will emerge as lobsters are brought into aquaculture setting and as fishing pressure intensifies with stocks become more susceptible to anthropogenic stressors.

Induction of lymphoidlike stroma and immune escape by tumors that express the chemokine CCL21

Tumor manipulation of host immunity is important for tumor survival and invasion. Many cancers secrete CCL21, a chemoattractant for various leukocytes and lymphoid tissue inducer cells, which drive lymphoid neogenesis. CCL21 expression by melanoma tumors in mice was associated with an immunotolerant microenvironment, which included the induction of lymphoid-like reticular stromal networks, an altered cytokine milieu, and the recruitment of regulatory leukocyte populations. In contrast, CCL21-deficient tumors induced antigen-specific immunity. CCL21-mediated immune tolerance was dependent on host rather than tumor expression of the CCL21 receptor, CCR7, and could protect distant, coimplanted CCL21-deficient tumors and even nonsyngeneic allografts from rejection. We suggest that by altering the tumor microenvironment, CCL21-secreting tumors shift the host immune response from immunogenic to tolerogenic, which facilitates tumor progression.

Transmural flow modulates cell and fluid transport functions of lymphatic endothelium

RATIONALE

Lymphatic transport of peripheral interstitial fluid and dendritic cells (DCs) is important for both adaptive immunity and maintenance of tolerance to self-antigens. Lymphatic drainage can change rapidly and dramatically on tissue injury or inflammation, and therefore increased fluid flow may serve as an important early cue for inflammation; however, the effects of transmural flow on lymphatic function are unknown.

OBJECTIVE

Here we tested the hypothesis that lymph drainage regulates the fluid and cell transport functions of lymphatic endothelium.

METHODS AND RESULTS

Using in vitro and in vivo models, we demonstrated that lymphatic endothelium is sensitive to low levels of transmural flow. Basal-to-luminal flow (0.1 and 1 mum/sec) increased lymphatic permeability, dextran transport, and aquaporin-2 expression, as well as DC transmigration into lymphatics. The latter was associated with increased lymphatic expression of the DC homing chemokine CCL21 and the adhesion molecules intercellular adhesion molecule-1 and E-selectin. In addition, transmural flow induced delocalization and downregulation of vascular endothelial cadherin and PECAM-1 (platelet/endothelial cell adhesion molecule-1). Flow-enhanced DC transmigration could be reversed by blocking CCR7, intercellular adhesion molecule-1, or E-selectin. In an experimental model of lymphedema, where lymphatic drainage is greatly reduced or absent, lymphatic endothelial expression of CCL21 was nearly absent.

CONCLUSIONS

These findings introduce transmural flow as an important regulator of lymphatic endothelial function and suggest that flow might serve as an early inflammatory signal for lymphatics, causing them to regulate transport functions to facilitate the delivery of soluble antigens and DCs to lymph nodes.

Vascular endothelial growth factor-C and C-C chemokine receptor 7 in tumor cell-lymphatic cross-talk promote invasive phenotype

Most carcinomas spread to distant sites through lymphatic vessels. Several preclinical and clinical studies have shown a positive correlation between the incidence of lymph node metastasis and secretion of the lymphatic growth factor vascular endothelial growth factor-C (VEGF-C) by tumor cells, suggesting tumor lymphangiogenesis as an escape mechanism. However, recent evidence has shown VEGF receptor-3 (VEGFR-3) expression on tumor cells and autocrine signaling, which increase metastatic potential. Furthermore, there is growing evidence implicating lymphatic-homing chemokine receptors, particularly C-C chemokine receptor 7 (CCR7), in lymph node metastasis. We report here that expressions of VEGF-C and CCR7 by tumor cells act synergistically to promote their invasion toward lymphatics. First, VEGF-C acts to increase lymphatic secretion of CCL21, which in turn drives CCR7-dependent tumor chemoinvasion toward lymphatics. Second, VEGF-C acts in an autocrine fashion to increase tumor invasiveness by increasing the proteolytic activity and motility of tumor cells in a three-dimensional matrix. Both of these effects are VEGFR-3 dependent and evident only in three-dimensional environments. We further verified that VEGF-C induces lymphatic CCL21 up-regulation in vivo by direct injection of VEGF-C protein intradermally in the mouse. Taken together, these results bridge the prometastatic functions of CCR7 and VEGF-C in tumors and show that, beyond lymphangiogenesis, VEGF-C promotes tumor invasion toward lymphatics by both autocrine and CCR7-dependent paracrine signaling mechanisms, which may be a significant cause of lymph node metastasis.

Autologous chemotaxis as a mechanism of tumor cell homing to lymphatics via interstitial flow and autocrine CCR7 signaling

CCR7 is implicated in lymph node metastasis of cancer, but its role is obscure. We report a mechanism explaining how interstitial flow caused by lymphatic drainage directs tumor cell migration by autocrine CCR7 signaling. Under static conditions, lymphatic endothelium induced CCR7-dependent chemotaxis of tumor cells through 3D matrices. However, interstitial flow induced strong increases in tumor cell migration that were also CCR7 dependent, but lymphatic independent. This autologous chemotaxis correlated with metastatic potential in four cell lines and was verified by visualizing directional polarization of cells in the flow direction. Computational modeling revealed that transcellular gradients of CCR7 ligand were created under flow to drive this response. This illustrates how tumor cells may be guided to lymphatics during metastasis.

Conservation in the first internal transcribed spacer region (ITS1) in Hematodinium species infecting crustacean hosts found in the UK and Newfoundland

Parasitic dinoflagellates in the genus Hematodinium infect a number of decapod crustaceans in waters off the UK, including the Norway lobster Nephrops norvegicus and the edible crab Cancer pagurus. This study investigated sequence variability in the first internal transcribed spacer (ITS1) region of the ribosomal RNA complex of Hematodinium spp. infecting N. norvegicus, C. pagurus, and Pagurus bernhardus from 4 locations in the UK and from the Hematodinium sp. infecting Chionoecetes opilio from the province of Newfoundland and Labrador, Canada. Phylogenetic analysis of the Hematodinium ITS1 sequences from N. norvegicus, C. pagurus, P. bernhardus and C. opilio suggest that these crustaceans are infected with the same species of Hematodinium. Length variability of the ITS1 region was observed (324 to 345 bp) and attributed to 4 variable microsatellite regions (CATG)n' (GCC)nTCCGC(TG)n' (TA)n' and (GAA)n(GGA)n within the sequenced ITS1 fragment. The observed variation may be due to co-infection of the host crustacean with several different strains of Hematodinium or differences among copies of ITS1 region within the genome of a single parasite cell. The Hematodinium ITS1 sequence from N. norvegicus, C. pagurus, P. bernhardus and C. opilio isolates was sufficiently conserved in primer binding regions targeted by previous molecular diagnostic assays; therefore, we suggest that this assay could be used to screen for Hematodinium infections in these crustacean hosts.

Differences in enzyme activities between two species of Hematodinium, parasitic dinoflagellates of crustaceans

Parasitic dinoflagellates of the genus Hematodinium infect several commercially important decapod crustaceans. Different species of Hematodinium have different levels of virulence in their respective hosts. Enzyme activities were studied from two species of Hematodinium, one isolated from the Norway lobster (Nephrops norvegicus) and the other from the American blue crab (Callinectes sapidus). We report the identification of differences in secretion of acid phosphatase (AP) and leucine arylamidase from two parasite species. Leucine arylamidase was only contained and secreted by the species infecting the blue crab. Both parasite species contained AP, but only the species infecting the Norway lobster secreted this enzyme. In this species, AP activity was predominantly in the soluble fraction (69.5%). AP activity was localized to cytoplasmic granules and on the membranes surrounding the cell nucleus. In addition to providing information on the cellular metabolism of the parasite, the pattern of activities of these enzymes may also be useful in distinguishing among different species of Hematodinium.

Cooperative and redundant roles of VEGFR-2 and VEGFR-3 signaling in adult lymphangiogenesis

Activation of vascular endothelial growth factor (VEGF) receptor-3 (VEGFR-3) by VEGF-C initiates lymphangiogenesis by promoting lymphatic proliferation and migration. However, it is unclear whether VEGFR-3 signaling is required beyond these initial stages, namely during the organization of new lymphatic endothelial cells (LECs) into functional capillaries. Furthermore, the role of VEGFR-2, which is also expressed on LECs and binds VEGF-C, is unclear. We addressed these questions by selectively neutralizing VEGFR-3 and/or VEGFR-2 for various time periods in an adult model of lymphangiogenesis in regenerating skin. While blocking either VEGFR-2 or VEGFR-3 with specific antagonist mAbs (DC101 and mF4-31C1, respectively) prior to lymphatic migration prevented lymphangiogenesis, blocking VEGFR-3 subsequent to migration did not affect organization into functional capillaries, and VEGFR-2 blocking had only a small hindrance on organization. These findings were confirmed in vitro using human LECs and anti-human antagonist mAbs (IMC-1121a and hF4-3C5): both VEGFR-2 and -3 signaling were required for migration and proliferation, but tubulogenesis in 3D cultures was unaffected by VEGFR-3 blocking and partially hindered by VEGFR-2 blocking. Furthermore, both in vitro and in vivo, while VEGFR-3 blocking had no effect on LEC organization, coneutralization of VEGFR-2, and VEGFR-3 completely prevented lymphatic organization. Our findings demonstrate that cooperative signaling of VEGFR-2 and -3 is necessary for lymphatic migration and proliferation, but VEGFR-3 is redundant with VEGFR-2 for LEC organization into functional capillaries.

Chemokine-mediated migration of melanoma cells towards lymphatics--a mechanism contributing to metastasis

The mechanisms that cause tumors such as melanomas to metastasize into peripheral lymphatic capillaries are poorly defined. Non-mutually-exclusive mechanisms are lymphatic endothelial cell (LEC) chemotaxis and proliferation in response to tumor cells (chemotaxis-lymphangiogenesis hypothesis) or LECs may secrete chemotactic agents that attract cancer cells (chemotactic metastasis hypothesis). Using migration assays, we found evidence supporting both hypotheses. Conditioned medium (CM) from metastatic malignant melanoma (MMM) cell lines attracted LEC migration, consistent with the lymphangiogenesis hypothesis. Conversely, CM from mixed endothelial cells or LECs, but not blood endothelial cells, attracted MMM cells but not non-metastatic melanoma cells, consistent with the chemotactic metastasis hypothesis. MMM cell lines expressed CCR7 receptors for the lymphatic chemokine CCL21 and CCL21 neutralizing antibodies prevented MMM chemotaxis in vitro. To test for chemotactic metastasis in vivo tumor cells were xenotransplanted into nude mice approximately 1 cm from an injected LEC depot. Two different MMM grew directionally towards the LECs, whereas non-metastatic melanomas did not. These observations support the hypothesis that MMM cells grow towards regions of high LEC density owing to chemotactic LEC secretions, including CCL21. This chemotactic metastasis may contribute to the close association between metastasizing tumor cells and peri-tumor lymphatic density and promote lymphatic invasion.

VEGF165b, an inhibitory vascular endothelial growth factor splice variant: mechanism of action, in vivo effect on angiogenesis and endogenous protein expression

Growth of new blood vessels (angiogenesis), required for all tumor growth, is stimulated by the expression of vascular endothelial growth factor (VEGF). VEGF is up-regulated in all known solid tumors but also in atherosclerosis, diabetic retinopathy, arthritis, and many other conditions. Conventional VEGF isoforms have been universally described as proangiogenic cytokines. Here, we show that an endogenous splice variant, VEGF(165)b, is expressed as protein in normal cells and tissues and is circulating in human plasma. We also present evidence for a sister family of presumably inhibitory splice variants. Moreover, these isoforms are down-regulated in prostate cancer. We also show that VEGF(165)b binds VEGF receptor 2 with the same affinity as VEGF(165) but does not activate it or stimulate downstream signaling pathways. Moreover, it prevents VEGF(165)-mediated VEGF receptor 2 phosphorylation and signaling in cultured cells. Furthermore, we show, with two different in vivo angiogenesis models, that VEGF(165)b is not angiogenic and that it inhibits VEGF(165)-mediated angiogenesis in rabbit cornea and rat mesentery. Finally, we show that VEGF(165)b expressing tumors grow significantly more slowly than VEGF(165)-expressing tumors, indicating that a switch in splicing from VEGF(165) to VEGF(165)b can inhibit tumor growth. These results suggest that regulation of VEGF splicing may be a critical switch from an antiangiogenic to a proangiogenic phenotype.

Infection experiments with Aphanomyces invadans in four species of estuarine fish

Along the eastern seaboard of the US, Atlantic menhaden, Brevoortia tyrannus, develop characteristic ulcerative lesions, a condition termed ulcerative mycosis. These lesions are identical to those seen across Asia in fish affected by epizootic ulcerative syndrome, a condition caused by the fungus-like oomycete Aphanomyces invadans. Young-of-the-year menhaden inhabiting estuarine environments are the primary species affected in the USA and little is known about the factors involved in the initiation of the lesions, or why menhaden are predominantly infected. Atlantic menhaden, hogchoker, Trinectus maculatus, striped killifish, Fundulus majalis, and mummichog, Fundulus heteroclitus, were inoculated with A. invadans (80 zoospores per fish) to explore species differences in infection and lesion development. All four species developed lesions. Killifish developed frank lesions similar to those observed in menhaden but the gross lesions occurred later, approximately 5-10 days after those on menhaden. Hogchoker and mummichog did not develop gross skin ulcers; rather, their lesions appeared as reddened areas under the epidermis. Mummichogs also showed evidence of significant healing with a well-developed granuloma and significant myocyte regeneration. These experiments show that species barriers as well as ecological barriers can explain some of the factors involved in the development of lesions in, and specificity of the water mould for, menhaden.

Lymphatic density and metastatic spread in human malignant melanoma

Malignant melanoma (MM), the most common cause of skin cancer deaths, metastasises to regional lymph nodes. In animal models of other cancers, lymphatic growth is associated with metastasis. To assess if lymphatic density (LD) was increased in human MM, and its association with metastasis, we measured LD inside and around archival MM samples (MM, n=21), and compared them with normal dermis (n=11), basal cell carcinoma (BCC, n=6) and Merkel cell carcinoma (MCC), a skin tumour thought to metastasise through a vascular route (MCC, n=6). Lymphatic capillary density (mm⁻²), as determined by immunohistochemical staining with the lymphatic specific marker LYVE-1, was significantly increased around MM (10.0±2.5 mm⁻²) compared with normal dermis (2.4±0.9 mm⁻²), BCC (3.0±0.9 mm⁻²) and MCC (2.4±1.4 mm⁻²) (P<0.0001). There was a small decrease in LD inside MM (1.1±0.7 mm⁻²) compared with normal dermis, but a highly significant decrease in BCC (0.14±0.13) and MCC (0.12±2.4) (P<0.01 Kruskal–Wallis). Astonishingly, LD discriminated between melanomas that subsequently metastasised (12.8±1.6 mm⁻²) and those that did not (5.4±1.1 mm⁻², P<0.01, Mann–Whitney). Lymphatic invasion by tumour cells was seen mainly in MM that metastasised (70% compared with 12% not metastasising, P<0.05 Fisher's Exact test). The results show that LD was increased around MMs, and that LD and tumour cell invasion of lymphatics may help to predict metastasis. To this end, a prognostic index was calculated using LD, lymphatic invasion and thickness that clearly discriminated metastatic from nonmetastatic tumours.

Functional significance of MMP-2 and MMP-9 expression by human malignant oral keratinocyte cell lines

This study examined the expression of MMP-2 and MMP-9 in normal and human malignant oral keratinocytes. The expression of pro-MMP-2 and pro-MMP-9 was heterogeneous in the malignant cell lines. Normal oral keratinocytes expressed less pro-MMP-2 and more pro-MMP-9 than their malignant counterparts. Cells that expressed high levels of both MMP-2 and MMP-9 showed the greatest degree of invasion through Matrigel in vitro compared to cells with either low or variable levels of these enzymes; normal keratinocytes were non-invasive in these conditions. The degree to which the cells invaded through Matrigel was similar to their motility in the absence of Matrigel and was not influenced by the activation of the pro-enzymes or the inhibition of enzyme activity using a chemical inhibitor of gelatinases. Cells were transplanted orthotopically to athymic mice and demonstrated a variable capacity not only to form tumours at the site of inoculation but, also, to metastasise; normal oral keratinocytes were non-tumorigenic. There was no correlation between the expression of either MMP-2 or MMP-9 and the tumorigenic/metastatic phenotype. The results emphasise the limitations of correlating in vitro and in vivo assays of tumour cell behaviour and suggest that invasion/motility in vitro may be a distinct phenotype from tumorigenicity/metastasis in vivo.

Are Pfiesteria species toxicogenic? Evidence against production of ichthyotoxins by Pfiesteria shumwayae

The estuarine genus Pfiesteria has received considerable attention since it was first identified and proposed to be the causative agent of fish kills along the mid-Atlantic coast in 1992. The presumption has been that the mechanism of fish death is by release of one or more toxins by the dinoflagellate. In this report, we challenge the notion that Pfiesteria species produce ichthyotoxins. Specifically, we show that (i) simple centrifugation, with and without ultrasonication, is sufficient to "detoxify" water of actively fish-killing cultures of Pfiesteria shumwayae, (ii) organic extracts of lyophilized cultures are not toxic to fish, (iii) degenerate primers that amplify PKS genes from several polyketide-producing dinoflagellates failed to yield a product with P. shumwayae DNA or cDNA, and (iv) degenerate primers for NRPS genes failed to amplify any NRPS genes but (unexpectedly) yielded a band (among several) that corresponded to known or putative PKSs and fatty acid synthases. We conclude that P. shumwayae is able to kill fish by means other than releasing a toxin into bulk water. Alternative explanations of the effects attributed to Pfiesteria are suggested.

VEGF165b, an inhibitory splice variant of vascular endothelial growth factor, is down-regulated in renal cell carcinoma

Angiogenesis is essential for tumor growth. Vascular endothelial growth factor (VEGF) is the most potent growth factor of tumor neovasculature, has been shown to be up-regulated in every tumor studied thus far, and is correlated with tumor stage and progression. To determine whether specific VEGF splice variants were differentially expressed in renal cell carcinomas, 18 polar tumor samples were analyzed by reverse transcription-PCR using primers designed to differentiate between VEGF splice variants. Control tissue was derived from the opposite normal pole. An amplicon of length consistent with the previously described variant VEGF(148) was found in normal kidney tissue. Subsequent sequencing revealed a new VEGF isoform formed by differential splicing from the end of exon 7 into the 3' untranslated region of the mRNA. Cloning of this transcript showed that translation would result in a 165-amino acid peptide with an alternative terminal 6 amino acids, followed by a stop codon. We have termed this new isoform VEGF165b. This isoform was present in 17 of 18 normal kidney samples but only 4 of 18 cases from matched malignant tissue. VEGF165b was therefore expressed in a significantly higher proportion of normal tissue than malignant tissue from the same patients (P < 0.001). To determine the functional significance of this new isoform, we expressed the full-length protein in a heterologous expression system. Conditioned medium containing this isoform significantly and dose dependently inhibited VEGF165-mediated proliferation, migration of endothelial cells, and vasodilatation of mesenteric arteries. This novel isoform VEGF165b is therefore an endogenous inhibitory form of VEGF that is down-regulated in renal tumors and, therefore, may be anti-angiogenesis.

Skin ulcers in estuarine fishes: a comparative pathological evaluation of wild and laboratory-exposed fish

The toxic dinoflagellate Pfiesteria piscicida Steidinger & Burkholder has recently been implicated as the etiologic agent of acute mass mortalities and skin ulcers in menhaden, Brevoortia tyrannus, and other fishes from mid-Atlantic U.S. estuaries. However, evidence for this association is largely circumstantial and controversial. We exposed tilapia (Oreochromis spp.) to Pfiesteria shumwayae Glasgow & Burkholder (identification based on scanning electron microscopy and molecular analyses) and compared the resulting pathology to the so-called Pfiesteria-specific lesions occurring in wild menhaden. The tilapia challenged by high concentrations (2,000-12,000 cells/mL) of P. shumwayaeexhibited loss of mucus coat and scales plus mild petecchial hemorrhage, but no deeply penetrating chronic ulcers like those in wild menhaden. Histologically, fish exhibited epidermal erosion with bacterial colonization but minimal associated inflammation. In moribund fish, loss of epidermis was widespread over large portions of the body. Similar erosion occurred in the mucosa lining the oral and branchial cavities. Gills exhibited epithelial lifting, loss of secondary lamellar structure, and infiltration by lymphoid cells. Epithelial lining of the lateral line canal (LLC) and olfactory organs exhibited severe necrosis. Visceral organs, kidney, and neural tissues (brain, spinal cord, ganglia, peripheral nerves) were histologically normal. An unexpected finding was the numerous P. shumwayae cells adhering to damaged skin, skin folds, scale pockets, LLC, and olfactory tissues. In contrast, histologic evaluation of skin ulcers in over 200 wild menhaden from Virginia and Maryland portions of the Chesapeake Bay and the Pamlico Estuary, North Carolina, revealed that all ulcers harbored a deeply invasive, highly pathogenic fungus now known to be Aphanomyces invadans. In menhaden the infection always elicited severe myonecrosis and intense granulomatous myositis. The consistent occurrence of this fungus and the nature and severity of the resulting inflammatory response indicate that these ulcers are chronic (age >1 week) and of an infectious etiology, not the direct result of an acute toxicosis initiated by Pfiesteria toxin(s) as recently hypothesized. The disease therefore is best called ulcerative mycosis (UM). This study indicates that the pathology of Pfiesteria laboratory exposure is fundamentally different from that of UM in menhaden; however, we cannot rule out Pfiesteria as one of many possible early initiators predisposing wild fishes to fungal infection in some circumstances.

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.

'Candidatus Xenohaliotis californiensis', a newly described pathogen of abalone, Haliotis spp., along the west coast of North America

Withering syndrome is a fatal disease of wild and cultured abalone, Haliotis spp., that inhabit the west coast of North America. The aetiological agent of withering syndrome has recently been identified as a member of the family Rickettsiaceae in the order Rickettsiales. Using a combination of morphological, serological, life history and genomic (16S rDNA) characterization, we have identified this bacterium as a unique taxon and propose the provisional status of 'Candidatus Xenohaliotis californiensis'. The Gram-negative, obligate intracellular pleomorphic bacterium is found within membrane-bound vacuoles in the cytoplasm of abalone gastrointestinal epithelial cells. The bacterium is not cultivable on synthetic media or in fish cell lines (e.g. CHSE-214) and may be controlled by tetracyclines (oxytetracycline) but not by chloramphenicol, clarithromycin or sarafloxicin. Phylogenetic analysis based on the 16S rDNA of 'Candidatus Xenohaliotis californiensis' places it in the alpha-subclass of the class Proteobacteria but not to the four recognized subtaxa of the alpha-Proteobacteria (alpha-1, alpha-2, alpha-3 and alpha-4). The bacterium can be detected in tissue squashes stained with propidium iodide, microscopic examination of stained tissue sections, PCR or in situ hybridization. 'Candidatus Xenohaliotis californiensis' can be differentiated from other closely related alpha-Proteobacteria by its unique 16S rDNA sequence.

Oculophryxus bicaulis, a new genus and species of dajid isopod parasitic on the euphausiid Stylocheiron affine Hansen

A new genus and species of dajid isopod is described from the euphausiid Stylocheiron affine Hansen. The isopod is a member of the Dajidae Krøyer, 1842, which are ectoparasites of shrimp, mysids, and krill. The female of the new genus and species is unique in its attachment to the eyestalk of its euphausiid host. The well-developed antennae encircle the eye peduncles of the host. The parasite presumably feeds by sucking blood directly from the head of the euphausiid. The new genus can be distinguished from other genera by the elongate, spoon-shaped antennae, the number of pereopods, and the indistinct abdomen. The male parasite attaches to the posterior of the female near the margin of the marsupium. The male can be distinguished from other genera by the rudimentary 7th pereopod. Epicaridia, microniscus and cryptoniscus larvae were not observed. The parasite was found in samples taken during 7 oceanographic surveys made along the west coast of Baja California. The parasite was found on the furciliae, juveniles, and immature males and females of S. affine. Female isopods may castrate their hosts as none of the infected hosts (n = 27) had reached maturity. Of the 3 eco-phenotypes of S. affine that are found in the region, the isopod apparently prefers the California Current morph. However, in the Gulf of Mexico, a similar parasite was found on S. longicorne Sars.

The impact of adults' communication clarity versus communication deviance on adolescents with learning disabilities

Research has demonstrated that confusing styles of parental communication--"communication deviances" (CD)--are associated with cognitive disorder in offspring. The present study examined the immediate effects of adult communication clarity versus deviance on sixty-one 11- to 15-year-old male and female adolescents with learning disabilities (LD). Subjects were randomly assigned to complete the Rorschach Arrangement Task (RorAT) under conditions of either clear (n = 30) or unclear (n = 31) instructions from an adult. Immediately thereafter, the adolescents were administered a test of abstract thinking--The Twenty Questions Task (TQT). Strategies used to solve the task were assessed. As hypothesized, adolescents in the clear communication condition performed significantly better on the RorAT and used more efficient cognitive strategies on the TQT than did adolescents in the unclear communication condition. A new theory with implications for teaching and parenting is proposed for understanding the influence of adult communication on students with LD.

The parallel process of resistance by clients and therapists to starting groups: a guide for nurses

Group psychotherapy is well recognized as a treatment modality with a powerful healing capacity. Yet, as experienced group therapists will attest, it is immensely difficult to begin a group. Assembling clients who have sufficiently dealt with their resistance to join a psychotherapy group is a painstaking process. Students in group psychotherapy training programs also find beginning a new group an arduous and frustrating task. The authors have had the benefit of postgraduate group psychotherapy training program to build on the expertise and skills already familiar to the Clinical Nurse Specialist. Our understanding of the parallel process in the resistance to beginning a group grew out of our training experience. We will explore within the parallel process framework some of the factors that make the development of a group psychotherapy practice as complex. Parallels will be drawn between clinician resistance to beginning a new group and client resistance to joining a group.

Rhizophydium littoreum on the Eggs of Cancer anthonyi: Parasite or Saprobe?

The relationship between host and symbiont is often difficult to assess and quantify. A novel technique that may help assess the host-symbiont relationship of organisms found in crab egg masses is described. This technique may have application in determining the relationship of other host-symbiont associations. Crab eggs were killed cryogenically and exposed in combinations with live eggs to a previously unreported symbiont of crab egg masses. The results indicated that the chytrid Rhizophydium littoreum is primarily a saprobe that attacks dead eggs; yet at high zoospore densities, it attacks and kills live eggs. Furthermore, R. littoreum is the first chytridiomycete to be reported from a marine crustacean host. It was highly prevalent on the eggs of its host and was found throughout the year.