Aims/hypothesis Alginate-encapsulated human islet cell grafts have not been able to correct diabetes in humans, whereas free grafts have. This study examined in immunodeficient mice whether alginate-encapsulated graft function was inferior to that of free grafts of the same size and composition. Methods Cultured human islet cells were equally distributed over free and alginate-encapsulated grafts before implantation in, respectively, the kidney capsule and the peritoneal cavity of non-obese diabetic mice with severe combined immunodeficiency and alloxan-induced diabetes. Implants were followed for in vivo function and retrieved for analysis of cellular composition (all) and insulin secretory responsiveness (capsules). Results Free implants with low beta cell purity (19±1%) were non-functional and underwent 90% beta cell loss. At medium purity (50±1%), they were functional at post-transplant week 1, evolving to normoglycaemia (4/8) or to C-peptide negativity (4/8) depending on the degree of beta cell-specific losses. Encapsulated implants immediately and sustainably corrected diabetes, irrespective of beta cell purity (16/16). Most capsules were retrievable as single units, enriched in endocrine cells that exhibited rapid secretory responses to glucose and glucagon. Single capsules with similar properties were also retrieved from a type 1 diabetic recipient at post-transplant month 3. However, the vast majority were clustered and contained debris, explaining the poor rise in plasma C-peptide. Conclusions/interpretation In immunodeficient mice, i.p. implanted alginate-encapsulated human islet cells exhibited a better outcome than free implants under the kidney capsule. They did not show primary non-function at low beta cell purity and avoided beta cell-specific losses by rapidly establishing normoglycaemia. Retrieved capsules presented secretory responses to glucose, which was also observed in a type 1 diabetic recipient.

Aims/hypothesis Neogenesis of beta cells and their clustering to small aggregates is a key process in prenatal development of beta cell mass. We investigated the contribution of postnatally formed small aggregates to functional beta cell mass in adult rats. Methods Conditions were defined for (1) counting total beta cell number in pancreases with relative error of <10% and (2) determining their distribution over aggregates of different size and over functionally different subpopulations. Results Pancreases of 10-week-old male Wistar rats contained 2.8±0.2×10 6 beta cells, of which >90% was generated postnatally, involving: (1) neo-formation of 30,000 aggregates with diameter <50 μm including single cells; and (2) growth of 5,500 aggregates to larger sizes, accounting for 90% of the increase in cell number, with number of growing aggregates in the tail 50% greater than elsewhere. At 10 weeks, 86% of aggregates were <50 μm; compared with aggregates >200 μm, their beta cells exhibited a higher basal insulin content that was also resistant to glibenclamide-induced degranulation. The pool of Ki67-positive beta cells was sixfold larger than at birth and distributed over all aggregate sizes. Conclusions/interpretation We describe a method for in situ counting of beta cell numbers and subpopulations with low relative error. In adult rats, >90% of beta cells and beta cell aggregates are formed after birth. Aggregates <50 μm are more than 100-fold more abundant than aggregates >200 μm, which are selected for isolated islet studies. Their topographic and functional properties contribute to the functional heterogeneity of the beta cell population; their growth to larger aggregates with characteristic beta cell functions may serve future metabolic needs.

Type 1 and type 2 diabetes have often been presented as disease forms that profoundly differ in the presence and pathogenic significance of a reduced b-cell mass. We review evidence indicating that the b-cell mass in type 1 diabetes is usually not decreased by at least 90% at clinical onset, and remains often detectable for years after diagnosis at age above 15 years. Clinical and experimental evidence also exists for a reduced b-cell mass in type 2 diabetes where it can be the cause for and/or the consequence of dysregulated b-cell functions. With b-cell mass defined as number of b-cells, these views face the limitation of insufficient data and methods for human organs. Because b-cells can occur under different phenotypes that vary with age and with environmental conditions, we propose to use the term functional b-cell mass as an assessment of a b-cell population by the number of b-cells and their phenotype or functional state. Assays exist to measure functional b-cell mass in isolated preparations. We selected a glucose-clamp test to evaluate functional b-cell mass in type 1 patients at clinical onset and in type 1 recipients following intraportal islet cell transplantation. Comparison of the data with those in non-diabetic controls helps targeting and monitoring of therapeutic interventions.

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Interleukin-8 (IL-8) is a chemokine that belongs to the α-chemokine or CXC subfamily and is produced by a wide variety of human cells, including monocytes and polymorphonuclear cells (PMN). IL-8 is secreted in response to inflammatory stimuli, notably bacterial products such as lipopolysaccharide (LPS), but little is known about the mechanisms by which these agents mediate IL-8 induction. In this report, we show that Mycoplasma fermentans lipid-associated membrane proteins (LAMPf) induce the production of high levels of IL-8 by THP-1 (human monocyte) cells and PMN at the same extent as LPS. It was previously demonstrated that stimulation of monocytic cells with either LPS or LAMPf led to a series of common downstream signaling events, including the activation of protein tyrosine kinase and of mitogen-activated protein kinase cascades. By using PD-98059 and SB203580, two potent and selective inhibitors of MEK1 (a kinase upstream of ERK1/2) and p38, respectively, we have demonstrated that both ERK1/2 and p38 cascades play a key role in the production of IL-8 by monocytes and PMN stimulated with bacterial fractions.