SUMMARYCD14, a GPI-linked membrane protein, is a component of the lipopolysaccharide (LPS) receptor complex, one of the pattern-recognizing receptors (PRR) expressed by myeloid lineage cells. Here we report that CD14, the functionally linked toll-like receptor molecules, TLR2 and TLR4, and the associated molecule MD-2 are expressed in endocrine cells of the human pancreatic islets. CD14 expression in human pancreatic islets was determined by immunofluorescence staining of tissue sections and primary cultures, and confirmed by flow cytometry of dispersed normal islets and SV40-transformed islet cells (HP62). The latter cells synthesized and secreted CD14 in response to lipopolysaccharide (LPS) in a time-and dose-dependent manner. Reverse transcription polymerase chain reaction (RT-PCR)-Southern was positive for CD14, TLR2, TLR4 and MD-2 in human pancreas, purified islets and HP62 cells. In vitro experiments using rat islets (also positive for CD14 by RT-PCR) and HP62 cells showed that LPS regulates glucose-dependent insulin secretion and induces inflammatory cytokines [interleukin (IL)-1 a , IL-6 and tumour necrosis factor (TNF)-a ]. The functional expression of CD14 and associated molecules in islet b cells adds a new pathway that islet cells may follow to adjust their function to endotoxaemia situations and become vulnerable to the inflammatory events that occur during diabetogenic insulitis.

We have used a reverse transcriptase-polymerase chain reaction (RT-PCR) protocol to examine the expression of cytokines in the pancreases and islets of patients with type I diabetes. We detect a significant increase in the level of expression of interferon (IFN)-alpha in the pancreases of the diabetic patients as compared with the control pancreases. In contrast, IFN-beta was detected at comparable levels in both groups, while IFN-gamma was detected in three of four control pancreases and one of four pancreases from the diabetic individuals. The IFN-alpha cDNAs generated by the RT-PCR were cloned and sequenced to determine which alpha-subtypes were being expressed. We found that the repertoire of subtypes was quite limited in any one individual (diabetic or not), although each individual was different with respect to the pattern of subtypes expressed. We also examined these pancreases for the expression of tumor necrosis factor (TNF)-alpha, interleukin (IL)-1 beta, IL-2, IL-4, and IL-6. We found no detectable expression of TNF-alpha or IL-2 in any pancreases, and the expression of the other cytokines was variable, with no pattern emerging from the comparison of the diabetic and nondiabetic individuals. We conclude that, of the cytokines examined, only IFN-alpha was significantly increased in the diabetic patients, a result that is consistent with the possibility that this cytokine is directly involved in the development of type I diabetes.

Clinical transplantation of human islets has a disappointingly low rate of success. We report here the identification of a possible causative factor: endotoxin present in the collagenase preparations used to disperse the pancreatic tissue before islet purification and transplantation. Supporting evidence includes (1) detection of unexpectedly high levels of endotoxin in most collagenase solutions currently used to digest human pancreases; (2) demonstration that supernatants generated during islet separation are able to induce the inflammatory cytokines interleukin (IL)-1, IL-6, and tumor necrosis factor-alpha (TNF-alpha) in macrophages; and (3) induction of IL-1, IL-6, and TNF-alpha in the islets during the separation procedure. Cytokine expression was assessed by reverse transcription-polymerase chain reaction and, for TNF-alpha, confirmed by enzyme-linked immunoabsorbent assay. It is proposed that endotoxin and locally induced cytokines carried over with the graft activate the endothelium and promote lymphomonocytic infiltration of grafted islets and surrounding liver tissue favoring primary nonfunction and early rejection. These results also have implications for the numerous experimental procedures that use collagenase, and they point to possible ways to improve islet preparation and transplantation protocols.

Understanding how T lymphocytes recognize beta-cell autoantigens is essential for the elucidation of the pathogenesis of insulin-dependent diabetes mellitus. The increased and ectopic expression of HLA class I and II molecules detected in human beta-cells may facilitate this interaction. T-lymphocyte recognition of surface antigens also involves adhesion accessory molecules: intercellular adhesion molecule 1 (ICAM-1) and lymphocyte function-associated antigen 3 (LFA-3). These molecules not only allow cell contact but can also provide costimulatory signals for T-lymphocyte activation. Levels of ICAM-1 and LFA-3 expression in normal human islet cells and regulation of their expression by cytokines interferon-gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta), and IL-6 have been studied by two-color immunofluorescence staining of pancreatic cryostat sections and fluorescence-activated cell sorter analysis. Neither ICAM-1 nor LFA-3 could be demonstrated in sections or in fresh cell preparations, but after 18 h of culture, beta-, alpha-, and delta-cells expressed spontaneously moderate levels of ICAM-1 (but not LFA-3). IFN-gamma and TNF-alpha alone or in combination strongly enhanced this spontaneous expression of ICAM-1 in a time- and/or dose-dependent and additive manner but had no effect on LFA-3. An SV40-transformed islet cell line showed high basal levels of both ICAM-1 and LFA-3, but the response to cytokines followed the same pattern as primary cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoimmune thyroid diseases (AITD) and insulin-dependent diabetes mellitus (IDDM) are two autoimmune syndromes of unknown etiology with common immune features. One is that the target cells, thyrocytes and pancreatic islet beta cells respectively, hyperexpress several proteins encoded in the HLA region: HLA class I, HLA class II and transporter associated with antigen processing (TAP-1): the clinical course and many aspects of the immunopathology are, however, quite different. Low-molecular-mass polypeptides 2 and 7 (LMP2 and LMP7) are proteasome subunits that increase the efficiency of endogenous antigen processing and are encoded in close vicinity to the TAP genes. We investigated whether LMP2 and LMP7 are hyperexpressed in thyrocytes and islet cells in AITD and IDDM. Thyroid tissue from Graves' disease patients (GD, n = 8) and Hashimoto thyroiditis (HT, n = 1) and pancreatic tissue from IDDM patients (n = 4) as well as control tissues were examined by the two-color indirect immunofluorescence technique. The results demonstrate that, in normal glands, thyrocytes and pancreatic islet cells express comparable moderate to low levels of LMP2 and LMP7. In AITD and IDDM, expression of LMP2/7 in the endocrine cells was disparate: while in AITD glands there was hyperexpression of LMP2 and 7 parallel to that of HLA class I and TAP-1, in the islet cells of recent onset diabetic pancreases (n = 2) the level of LMP2 and 7 expression was totally normal, including islets that were infiltrated by lymphocytes and hyperexpressed HLA class I and TAP-1. These observations suggest different mechanisms of endogenous peptides generation at the target cells in AITD from IDDM. Since this is a key step for the maintenance of peripheral tolerance, it may help to understand some of the different clinical features of the two autoimmune diseases.