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There is a need for better understanding of the biocompatibility of alginate-polycation microcapsules based on their physicochemical characteristics. Microcapsules composed of alginate with 44% (IntG) or 71% (HiG) guluronate, gelled with calcium (Ca) or barium (Ba) and coated with poly-L-lysine (PLL) or poly-l-ornithine (PLO), followed by IntG alginate were compared. For microcapsules with an IntG(Ca) gel core, using PLO instead of PLL resulted in less immune cell adhesion after 2 days in C57BL/6J mice. The PLO microcapsules were also characterized by greater hydrophilicity and superior resistance to swelling and damage under osmotic stress. For microcapsules with a PLL membrane, replacing the IntG(Ca) gel core with IntG(Ba) or HiG(Ca) gel resulted in stronger immune responses (p

Alginate purification has been shown to decrease the host immune response to implanted alginate-based microcapsules, but the direct effect of contaminants on islet cell survival remains unknown. Wistar rat islets were immobilized in calcium alginate beads made with crude vs. purified alginate and then incubated in CMRL culture medium. Islet survival was evaluated at 1, 4, 7, 14 and 27 days post-encapsulation. Islet viability was investigated using a dual staining assay (propidium iodide and orange acridine). The islet cell necrosis and the proportion of apoptotic cells were quantified under optical microscopy and with a TUNEL assay, respectively. Islets immobilized in purified alginate were more viable, and had fewer necrotic centers, a smaller area of central necrosis and a lower number of apoptotic cells. At day 14 and 27 post-encapsulation, respectively, 48% and 23% of islets were viable with purified alginate vs. 18% and 8% with crude alginate (p

CD47 is a ubiquitously expressed molecule which has been attributed a role in many cellular processes. Its role in preventing cellular phagocytosis has defined CD47 as an obligatory self-molecule providing a 'don't-eat-me-signal'. Additionally, CD47-CD172a interactions are important for cellular trafficking. Yet, the contribution of CD47 to T cell stimulation remains controversial, acting sometimes as a co-stimulator and sometimes as an inhibitor of TCR signalling or peripheral T cell responses. Most of the experiments leading to this controversy have been carried in in vitro systems. Moreover, the role of CD47 on thymocyte differentiation, which precisely relies on TCR signal strength, has not been evaluated. Here, we examine the in vivo role of CD47 in T cell differentiation using CD47-deficient mice. We find that, in the absence of CD47, thymocyte positive and negative selection processes are not altered. Indeed, our data demonstrate that the absence of CD47 does not influence the strength of TCR signalling in thymocytes. Furthermore, in agreement with a role for CD47-CD172a interactions in CD172a(+) dendritic cell migration, we report a reduced proportion of thymic dendritic cells expressing CD172a in CD47-deficient mice. As the total proportion of dendritic cells is maintained, this creates an imbalance in the proportion of CD172a(+) and CD172a(low) dendritic cells in the thymus. Together, these data indicate that the altered proportion of thymic dendritic cell subsets does not have a primordial influence on thymic selection processes.

233 (score 1.02 ± 0.03). This difference in biocompatibility was significant (p < 0.001). Yet, alginate hydrophilicity was similar, as water droplets on dry films had contact angles of 38.7 ± 1.7° and 39.0 ± 1.3° for Alg I and Alg II, respectively. When PLL was added to the capsule membrane, the immune response was more severe (p < 0.01), as cell adhesion scores increased to 1.11 ± 0.11 for Alg I and to 1.55 ± 0.07 for Alg II. Similarly, the cell adhesion score increased to 0.49 ± 0.06 when PLO was added to Alg I capsules, indicating a non-significant increase in capsule immunogenicity. A comparison of contact angles of water on dry films containing polycations was not possible due to irregular surfaces and complete wetting. We are currently measuring the contact angles of air bubbles on hydrated films. conclusions: The guluronic acid content of alginate has a significant effect on its biocompatibility in vivo. Incorporating polycations into the membranes of alginate microcapsules lowers their biocompatibility. So far, these results cannot be explained by the hydrophilicity of the samples. Transplantation islet and pancreas No conflict of interest

s / Can J Diabetes 37 (2013) S13eS84 S22 lancingwas also higher than the experienced pain (median 26 [IQR 11 to 35] mm versus 18 [IQR 6 to 26] mm; p

Islet transplantation has normalized the blood glucose levels in patients with type 1 diabetes. However, this treatment requires the use of potentially harmful immunosuppressive drugs. An alternative to immunosuppression is the use of semi-permeable microcapsules that allow the diffusion of glucose, nutrients and oxygen but protect the transplanted cells against immune reaction. Another important problem is the limited survival of encapsulated and free islet cells. Pancreatic duct cells have been shown to play an important role in pancreas morphogenesis. The co-incubation of pancreatic duct cells and islets has decreased cell apoptosis and necrosis in the immediate post-isolation period. We have previously shown that incubating islets with IGF-II, the principal peptide that is secreted by duct cells, diminishes apoptosis and necrosis of encapsulated islets and allows the restoration of euglycaemia in diabetic mice using fewer islets. The objective of this study is to investigate the effect of co-encapsulating islets with pancreatic duct cells on islet cell survival. Pancreatic duct cells were isolated from C57BL/6 mice and their identity was confirmed by immunohistochemistry using antibodies against cytokeratin 7 (CK7) and IGF-II. The presence of known contaminants (fibroblasts and mesenchymals cells) was investigated by flow cytometry using their common marker: vimentin. Islets encapsulated alone or co-encapsulated with two different concentrations of duct cells (20 or 100 cells per capsule) were maintained in culture and evaluated at days 1, 7, 14 and 27 postencapsulation. Islet viability was evaluated using fluorescent dyes (acridine orange and propidium iodide), the percentage of necrotic islets by inverted-microscope analysis and their function by an MTS test. Duct cells expressed IGF-II and CK7. The cell preparation was pure at >85%. Islets cell viability was between 60-80% for islets encapsulated alone or with duct cells with no significant difference. This coencapsulation did not have a significant impact on the islets necrosis which remained consistently between 30-40%. Co-encapsulating islets with 100 duct cells had a significant impact on islet function (vs. islets encapsulated alone). This was demonstrated by the MTS test, which showed an absorbance at 492 nm of 0.32 ± 0.06 for co-encapsulated islets (vs 0.09 ± 0.01; p