Immune and autoimmune aspects of diabetes mellitus

The immune and autoimmune aspects of diabetes mellitus are reviewed. Emphasis is given to the clinical association of diabetes with other autoimmune disease; the increased incidence of organ-specific autoimmunity in diabetic patients; the occurrence of humoral and cell-mediated antipancreas (islet) autoimmunity in diabetes; the association of HLA with juvenile-onset, insulin-dependent diabetes mellitus and with certain specific subpopulations of diabetic patients; the possible role of viruses in the etiology of diabetes; and the occurrence of alterations in humoral and cell-mediated immunity, granulocyte function, and the host defense against infectious agents in human diabetics and in animals with experimental diabetes.     

Interleukin-2 inhibits the synthesis and release of prolactin from human decidual cells

PRL is synthesized and released by several extrapituitary tissues, including decidualized endometrial stromal cells. As interleukin-2 (IL-2) stimulates the synthesis and release of pituitary PRL, and decidual stromal cells have receptors for IL-2, we examined whether IL-2 also regulates the release of decidual PRL. Exposure of primary cultures of human decidual cells (10(6) cells/well) from term pregnancies to IL-2 (50 ng/mL) inhibited PRL release beginning 48 h after exposure. The inhibition by IL-2 was dose dependent, and the maximal inhibition of PRL release after 5 days of exposure to IL-2 was 71.0 +/- 0.9% (mean +/- SE). IL-2, however, had no effect on decidual cell viability. The inhibitory effect of IL-2 on PRL release was secondary to inhibition of PRL synthesis. Decidualized human endometrial stromal cells transfected with 3 kb of the extrapituitary PRL (exon 1a) promoter coupled to a luciferase expression vector responded to IL-2 (10 ng/mL) with a significant decrease in luciferase activity. These findings strongly suggest that IL-2 inhibits the synthesis and release of decidual PRL and provide further support for a critical role of cytokines in the regulation of decidual PRL gene expression.     

Cyclic adenosine-3',5'-monophosphate stimulates the acute release of placental lactogen from human trophoblast cells

cAMP has been shown to be a second messenger in the release of many hormones and other secretory products. To determine whether cAMP also plays a role in the mechanism of release of human placental lactogen (hPL), we examined the effects of (Bu)2cAMP, isobutyl methylxanthine, forskolin, and cholera toxin on the acute release of hPL from an enriched fraction of hPL-producing trophoblast cells. Static cultures of trophoblast cells exposed to (Bu)2cAMP (5 mM) for 2 h released 2.6 times as much hPL as control cells (P less than 0.01) during the first 0.5 h of exposure. The increase in hPL release was followed by a decrease rate of release during the subsequent 1.5 h. Perifused trophoblast cells (1.5 X 10(6) exposed to 5 mM cAMP for 20 min released 3.2 times as much hPL as control cells. The rate of hPL increased markedly during the first 10 min of exposure, rapidly decreased toward control values during the remainder of the exposure period, and then declined to a subnormal rate for the next 30 min before returning to normal to control values. (Bu)2cAMP, however, had no acute effects on the release of human CG or the release of the cytosolic enzymes alkaline phosphatase and lactic dehydrogenase. The phosphodiesterase inhibitors theophylline (5 mM) and isobutyl methylxanthine (0.5 mM) and the adenylate cyclase activators forskolin (5 micrograms/ml) and cholera toxin (25 micrograms/ml) stimulated hPL release by 75-95%. These results strongly suggest that cAMP is a second messenger in the acute release of hPL.     

Demonstration that monocytes rather than lymphocytes are the insulin-binding cells in preparations of humah peripheral blood mononuclear leukocytes: implications for studies of insulin-resistant states in man.

Insulin receptors have been demonstrated on mononuclear leukocytes prepared by centrifugation of buffy coats from normal blood donors on Ficoll-Hypaque gradients. The cell type that specifically binds insulin in this mixture of lymphocytes and monocytes has never been clearly identified, although it was assumed to be the lymphocyte since this cell constitutes about 80% of the population. In the present studies, insulin-binding assays were performed on the mononuclear leukocyte preparation before and after selective depletion or enrichment for monocytes using glass wool or Sephadex G-10 adherence columns. The amount of 125-I-labeled insulin specifically bound correlated significantly with the number of monocytes but not with the number of B or T lymphocytes. Approximately 90% of the specific insulin binding of this preparation could be accounted for by its content of monocytes. The amount of binding was unaffected by phagocytosis of latex particles or by metabolic inhibitors added to prevent endocytosis. Autoradiograms made on smears of whole peripheral blood and mononuclear leukocytes demonstrated that all of the cells that bound 125-I-labeled insulin were large mononulcear cells, 85-90% of which could be identified as monocytes by morphological criteria or by the functional criterion of latex particle ingestion. Since insulin receptor concentration may be altered in disease states in man, it is essential, when using this cell population for detecting such changes, to quantitate the number of monocytes in the preparation so that the insulin-binding data can be appropriately interpreted.     

Spontaneous formation of germinal centers in autoimmune mice

The mechanisms of autoantibody production are not well understood. Germinal centers (GC) may be important sites of immune disregulation in autoimmune diseases. In this study, we document the presence of spontaneous GC formation in the spleens of several autoimmune mouse strains that spontaneously develop autoimmune Type I diabetes and a lupus-like disease. In contrast, mouse strains that do not develop lupus did not exhibit spontaneous formation of GC. In all of the autoimmune strains studied, GC were present at 1-2 months of age, a time that closely parallels the appearance of autoantibodies. Like the GC that develop after purposeful immunization, GC in autoimmune mice contained B220(+), PNA(+), and GL-7(+) B cells, and FDC-M1(+) follicular dendritic cells. In addition, spontaneously formed GC in autoimmunity and those caused by immunization were abrogated in a similar way by a short-term treatment with anti-CD40 ligand antibody. These data indicate that spontaneously forming GC in autoimmunity are similar to those appearing after purposeful immunization.     

Relaxin stimulates the synthesis and release of prorenin from human decidual cells: evidence for autocrine/paracrine regulation

Porcine relaxin caused a time- and concentration-dependent increase in the release of renin from decidual cells cultured over a 96 h period. The increase in renin release occurred 24-48 h after exposure and was maximal at 48-72 h. Half-maximal stimulation occurred at a relaxin concentration of 5 ng/ml, and maximal stimulation (250-270%) occurred at concentrations greater than or equal to 10 ng/ml. At each time, greater than 95% of the renin released into the medium was in the form of prorenin. The stimulation of renin release was paralleled by a stimulation of cellular renin content and was completely inhibited by cycloheximide, indicating that relaxin also stimulated renin synthesis. Since renin is present in both cytotrophoblast and decidual cells, these results suggest a paracrine and/or autocrine relationship between relaxin- and prorenin-secreting cells.     

Penicillin-binding proteins of penicillin-susceptible and -resistant pneumococci: immunological relatedness of altered proteins and changes in peptides carrying the beta-lactam binding site

There are several major differences between the penicillin-binding proteins (PBPs) of highly penicillin-resistant and -susceptible strains of pneumococci. The highest-molecular-size PBP 1a (98 kilodaltons [kDa]) of susceptible pneumococci is not detectable in resistant bacteria. Instead, resistant strains contain a PBP of smaller size: 92 and 94 kDa in South African strains 8249 and A95210, respectively, and 96 kDa in New Guinea strain 2955 (S. Zighelboim and A. Tomasz, Antimicrob. Agents Chemother. 17:434-442, 1980). Using antibodies prepared against PBP 1a of penicillin-susceptible pneumococci, we demonstrated that these anomalous-sized proteins in the resistant strains are immunologically related to PBP 1a of penicillin-susceptible bacteria. A second difference between the PBP patterns of strain 8249 and the susceptible pneumococci is that the 78-kDa PBP 2b is not detectable by the radioactive penicillin binding assay in the resistant strain. Using antibodies prepared against PBP 2b of susceptible cells, we demonstrated the presence of PBP 2b in membrane preparations from strain 8249 cells. Thus, the poor detection of this PBP appears to be related to its greatly decreased affinity for the antibiotic molecule. We also compared the patterns of penicillin-labeled peptides derived from PBPs of resistant and susceptible cells during partial proteolysis by V8 protease. Several changes were observable in small peptides carrying the beta-lactam binding site generated from the high Mr (PBP 1a-related) binding proteins. In contrast, no differences in the pattern of penicillin-labeled peptides were seen when the pattern of PBP 2a of susceptible pneumococci was compared with the peptide pattern of PBP 2a from resistant strains. One of the resistant isolates (strain 2955) also had a PBP 3 with a higher-than-normal molecular weight. This protein gave strong positive reaction with antibodies against PBP 3 of susceptible cells. Examination of the pattern of penicilloyl peptides generated from the susceptible and resistant PBP 3s during partial proteolysis revealed only differences which seem to reside distant from the beta-lactam binding site.     

Stimulation of resting normal human peripheral blood mononuclear cells by fetal calf sera. Activation to an interleukin-2 responsive state

Normal adult human peripheral blood mononuclear cells which are negative for interleukin-2 (IL-2) receptors as assessed by flow cytofluorometry, acquire IL-2 receptors and IL-2 responsiveness after culture in media supplemented with fetal calf sera. Thus, in the absence of any known external stimuli, fetal calf sera used to supplement culture media can induce the transformation of resting (G0) peripheral blood mononuclear cells to an activated (G1) state. The activated (G1) cells are able to progress through the rest of the cell cycle (S, G2, M) in the presence of IL-2. As a result, studies of human peripheral blood mononuclear cells in fetal calf serum-supplemented culture media should be interpreted with appropriate caution.