Islets of Langerhans isolated from the pancreas and encapsulated in alginate-polylysine-alginate micro-spheres can potentially serve as a self-regulating supply of insulin in response to glucose loads. A longitudinal ultrastructural and immunohistochemical study of encapsulated rat islets cultured in CMRL-1969 media at a constant glucose concentration of 5.5 mmol/L (100 mg%) allowed several observations. First, acinar cells, which remain attached to isolated islets, disappeared within 1 wk in tissue culture. Damaged endocrine cells also disappeared at this time. Phagocytic cells having ultrastructural features suggesting that they are macrophages emerged from the islets within about a week and ingested portions of the inner layer of capsule polymer. These macrophage-like cells retained these polymers until their death which occurred at around 1-2 mo after isolation; at no time did we observe phagocytic cells actually breaching the microsphere capsules. Beta cells remained well-granulated over 90 days of culture but accumulated lipofuscin-like residual bodies. Under these conditions, these bodies began to accumulate appreciably after about one week in culture.

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PubMedDate not supplied

Islet allograft rejection in rats: a time course study characterizing adhesion molecule expression, MHC expression, and infiltrate immunophenotypes.

Wistar Furth (RT1u) islets transplanted under the renal capsules of streptozotocin-diabetic Lewis (RT1l) rats reject after 5-6 days of normoglycemia. Hand-picked WF islets (1500-2000) were transplanted under the kidney capsules of diabetic Lew or WF rats. Rats bearing iso- or allografts were killed on posttransplant days 2, 4, and 6. Serial frozen sections of grafts and controls were stained by immunoperoxidase for rat MAC-1, class II MHC, CD2, CD4, CD8, B-cells, VLA-4, LFA-1, L-selectin, ICAM-1, and VCAM-1. Infiltrating cells, parenchymal cells, and endothelial cells in five distinct compartments (i.e., peritoneal reflection, subcapsular perivascular space, islet grafts, graft-kidney interface, and kidney) were evaluated for expression of the various markers at each interval. Significant infiltrates arrived in three distinct waves in both iso- and allografts. First, macrophages blanketed the peritoneal capsular reflection and infiltrated by day 2. Second, the first wave of lymphocytes arrived in the edematous subcapsular soft tissue via capsular vessels by day 2 (allo > iso). Third, the second wave of lymphocytes arrived from the renal parenchyma to form a dense band at the graft-kidney interface and around grafts by days 4 and 6 (allo >>> iso); CD4+ cells vastly outnumbered CD8+ cells, with CD4+ cells being mobilized first and from interstitial vessels throughout the entire kidney. CD8+ cells emigrated only from renal interstitial vessels adjacent to the graft. Large numbers of L-selectin+, VLA-4+, and LFA-1+ cells were seen in the infiltrates with the most intensely staining cells being intravascular. B-cells composed a very small proportion of infiltrating cells in both allo- and isografts. Endothelial staining for ICAM-1 and VCAM-1 was prominent throughout. Both class II MHC and ICAM-1 expression were induced on renal tubular epithelial cells, but neither was found on islet parenchymal cells. In conclusion, this study shows that islet allograft rejection is more complex than previously realized.

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