Prokaryotic expression and characterization of the heterodimeric construction of ZnT8 and its application for autoantibodies detection in diabetes mellitus.

BACKGROUND: In the present work we described the recombinant production and characterization of heterodimeric construction ZnT8-Arg-Trp325 fused to thioredoxin using a high-performance expression system such as Escherichia coli. In addition, we apply this novel recombinant antigen in a non-radiometric method, with high sensitivity, low operational complexity and lower costs. RESULTS: ZnT8 was expressed in E. coli as a fusion protein with thioredoxin (TrxZnT8). After 3 h for induction, recombinant protein was obtained from the intracellular soluble fraction and from inclusion bodies and purified by affinity chromatography. The expression and purification steps, analyzed by SDS-PAGE and western blot, revealed a band compatible with TrxZnT8 expected theoretical molecular weight (≈ 36.8 kDa). The immunochemical ability of TrxZnT8 to compete with [35S]ZnT8 (synthesized with rabbit reticulocyte lysate system) was assessed qualitatively by incubating ZnT8A positive patient sera in the presence of 0.2-0.3 µM TrxZnT8. Results were expressed as standard deviation scores (SDs). All sera became virtually negative under antigen excess (19.26-1.29 for TrxZnT8). Also, radiometric quantitative competition assays with ZnT8A positive patient sera were performed by adding TrxZnT8 (37.0 pM-2.2 µM), using [35S]ZnT8. All dose-response curves showed similar protein concentration that caused 50% inhibition (14.9-0.15 nM for TrxZnT8). On the other hand, preincubated bridge ELISA for ZnT8A detection was developed. This assay showed 51.7% of sensitivity and 97.1% of specificity. CONCLUSIONS: It was possible to obtain with high-yield purified heterodimeric construction of ZnT8 in E. coli and it was applied in cost-effective immunoassay for ZnT8A detection.

Flow cytometric microsphere-based immunoassay as a novel non-radiometric method for the detection of glutamic acid decarboxylase autoantibodies in type 1 diabetes mellitus.

The first measurable sign of arising autoimmunity in type 1 diabetes mellitus is the detection of autoantibodies against beta-cell antigens, such as glutamic acid decarboxylase (GAD65). GAD65 autoantibodies (GADA) are usually measured by the Radioligand Binding Assay (RBA). The aim of this work was to develop protocols of flow cytometric microsphere-based immunoassays (FloCMIA) which involved glutamic acid decarboxylase fused to thioredoxin (TrxGAD65) adsorbed on polystyrene microspheres. Detection of bound GADA was accomplished by the use of anti-human IgG-Alexa Fluor 488 (protocol A), anti-human IgG-biotin and streptavidin-dichlorotriazinyl aminofluorescein (DTAF) (protocol B) or TrxGAD65-biotin and streptavidin-DTAF (protocol C). Serum samples obtained from 46 patients assayed for routine autoantibodies at Servicios Tecnológicos de Alto Nivel (STAN-CONICET) were analyzed by RBA, ELISA and three alternative FloCMIA designs. Protocol C exhibited the highest specificity (97.8%) and sensitivity (97.4%) and a wide dynamic range (1.00-134.40 SDs). Samples obtained from 40 new-onset diabetic patients were also analyzed to further evaluate the performance of protocol C. The latter protocol showed a sensitivity of 58.6% and a prevalence of 47.5%. Two patients resulted positive only by FloCMIA protocol C and its SDs were higher than those of RBA and ELISA, showing a significantly wide dynamic range. In conclusion, FloCMIA proved to be highly sensitive and specific, requiring a low sample volume; it is environmentally adequate, innovative and represents a cost-effective alternative to traditional GADA determination by RBA and/or ELISA, making it applicable to most medium-complexity laboratories.

Expression of recombinant glutamic acid decarboxylase in insect larvae and its application in an immunoassay for the diagnosis of autoimmune diabetes mellitus.

Autoimmune Diabetes Mellitus (DM) is a chronic disease caused by the selective destruction of insulin producing beta cells in human pancreas. DM is characterized by the presence of autoantibodies that bind a variety of islet-cell antigens. The 65 kDa isoform of glutamate decarboxylase (GAD65) is a major autoantigen recognized by these autoantibodies. Autoantibodies to GAD65 (GADA) are considered predictive markers of the disease when tested in combination with other specific autoantibodies. In order to produce reliable immunochemical tests for large scale screening of autoimmune DM, large amounts of properly folded GAD65 are needed. Herein, we report the production of human GAD65 using the baculovirus expression system in two species of larvae, Rachiplusia nu and Spodoptera frugiperda. GAD65 was identified at the expected molecular weight, properly expressed with high yield and purity in both larvae species and presenting appropriate enzymatic activity. The immunochemical ability of recombinant GAD65 obtained from both larvae to compete with [35S]GAD65 was assessed qualitatively by incubating GADA-positive patients' sera in the presence of 1 µM of the recombinant enzyme. All sera tested became virtually negative after incubation with antigen excess. Besides, radiometric quantitative competition assays with GADA-positive patients' sera were performed by adding recombinant GAD65 (0.62 nM-1.4 µM). All dose response curves showed immunochemical identity between proteins. In addition, a bridge-ELISA for the detection of GADA was developed using S. frugiperda-GAD65. This assay proved to have 77.3% sensitivity and 98.2% of specificity. GAD65 could be expressed in insect larvae, being S. frugiperda the best choice due to its high yield and purity. The development of a cost effective immunoassay for the detection of GADA was also afforded.

Development of 2 alternative enzyme-linked immunosorbent assays for routine screening of glutamic acid decarboxylase autoantibodies.

BACKGROUND: Antibodies to GAD65 (GADA) are considered highly predictive humoral markers of the type 1 diabetes mellitus and also of the insulin requirement in adult-onset patients presumptively classified as type 2 diabetics or LADA. METHODS: We present 2 methods for GADA assessment. The first one (fluid phase, ELISA Protocol A) is carried out in a 2-step procedure in which serum GADA are first allowed to react with a fixed dose of GAD65-biotin in solution and the residual free antigen is later assayed by a conventional ELISA. In the second test (solid phase, ELISA Protocol B) GADA are measured in an ELISA that depends on the ability of divalent autoantibodies to form a bridge between immobilized TrxGAD65 and liquid-phase biotinylated TrxGAD65. RESULTS: All normal control samples scored negative in both variants of ELISA and RBA, hence specificity was 100% for all methods; the relative sensitivity of ELISA Protocol A respect of the RBA was 94% and that of ELISA Protocol B was 76%. CONCLUSIONS: Although ELISA Protocol A exhibited a better performance in terms of relative sensitivity than ELISA Protocol B, the simplicity of execution and the intended use of the assay must also be taken in consideration for the final choice.

Regional differences in astrocyte activation in HIV-associated dementia.

Since astrogliosis is a histological marker usually observed in HIV-associated dementia (HIV-D), we decided to investigate the potential relationship between the expression of glial fibrillary acidic protein (GFAP) and the regional distribution of cells positive (+) for this specific marker of astrocyte activation. Histological sections of brain tissues obtained at necropsy from 5 HIV-D patients and 5 age-matched controls without history of neuropsychiatric illness were immunostained with peroxidase. Mean numbers of GFAP(+) astrocytes were significantly increased in entorhinal cortex, hippocampus and subcortical white matter of patients, but values in frontal cortex and basal ganglia were similar to those of controls. In contrast, surface density of immunoreactive GFAP was significantly increased in all tested brain areas from all patients, including unusually affected regions such as entorhinal cortex and hippocampus. Therefore, such consistent finding of hypertrophic astrocytes, ranging from highest cell percentajes in subcortical white matter to lowest in basal ganglia indicates that quantification of surface density in GFAP (+) cells appears to be a more reliable approach to score gliosis than the counting of their cell nuclei. Because astrocyte activation involves both protective and detrimental effects on adjacent neuronal subsets, the evidence of regional differences in this reactive potential highlights the importance of accurately defining their contribution to the neuropathogenesis not only of HIV-D, but of a wide range of neurodegenerative disorders.

Characterization of zinc transporter 8 (ZnT8) antibodies in autoimmune diabetic patients from Argentinian population using monomeric, homodimeric, and heterodimeric ZnT8 antigen variants.

OBJECTIVE: In order to gain further knowledge of the structure of zinc transporter 8 (ZnT8) epitopes, we studied the role of the amino acid at position 325 in the antigen and its dimeric conformation for autoantibodies to ZnT8 (ZnT8A) recognition. METHODS: For this purpose, several ZnT8 C-terminal domain variants were designed: monomer carrying Arg325 or Trp325, homo-dimers ZnT8-Arg-Arg325 and ZnT8-Trp-Trp325, and hetero-dimer ZnT8-Arg-Trp325. Two groups of Argentinian diabetic patients were subjected to analysis using [(35)S]-ZnT8 variants by radioligand binding assay (RBA): i) 100 new-onset, insulin-dependent, type 1 diabetic patients and ii) 282 slowly progressing to insulin requirement, non-obese adult-onset diabetic patients. In addition, 50 type 1 diabetic patients and 100 normal control sera provided by the American Diabetes Association (ADA) were evaluated in order to calculate the sensitivity and specificity of ZnT8A assays for each antigenic variant. Other routine ß-cell autoantibodies were also tested by RBA. RESULTS: Of the 100 Argentinian type 1 diabetic patients, 65 were ZnT8A+. Out of them, 8 patients recognized all recombinant forms of ZnT8 and most patients (56) reacted against the heterodimer. Additionally, out of 282 non-obese adult-onset diabetic patients 46 were ZnT8A+, whereas 29 patients recognized only dimers. Besides, exclusive reactivity against ZnT8A was found in 9.0% for type 1 diabetes mellitus and 10.3% for non-obese adult-onset diabetic patients. CONCLUSIONS: Significantly higher signal values in RBA were obtained with the heterodimeric variant. An increased detection of humoral autoimmunity was found in both groups when ZnT8A was employed in combination with the other ß-cell autoantibodies. The inclusion of homodimeric immunoreactive peptides revealed the existence of quaternary structure-defined epitopes probably resembling the actual state of the autoantigen in vivo. Finally, the differential profiles of ZnT8A exhibited by type 1 and non-obese adult-onset diabetic patients suggest the different nature of autoimmune processes underlying both pathologies.

Immunochemical and morphometric features of astrocyte reactivity vs. plaque location in Alzheimer's disease.

The quantitative relationship between glial fibrillary acidic protein (GFAP) hyper-reactivity and beta-amyloid protein (betaAP) deposition was investigated by double immunoperoxidase labeling of hippocampal and entorhinal cortex sections from five Alzheimer's disease (AD) cases and five age-matched controls. betaAP plaques, which were absent in controls, were found in all AD samples, without significant differences in number or perimeter according to their location among the regions studied. In contrast, the mean number of GFAP (+) cells was significantly greater in the hippocampus than in the entorhinal cortex from AD cases (49 vs.39). Although at lower values (30 vs. 20), predominance of astrocyte hyperplasia in hippocampus as compared with entorhinal cortex was also found in control samples. Concomitant astrocyte hypertrophy, as defined by surface density (Sv) values of GFAP-immunoreactive material exceeding those of control means, affected a similar proportion of cells in the hippocampus (73%) and the entorhinal cortex (74%) from AD cases. Since an increased number of GFAP (+) cells in the hippocampus was not accompanied by an increased number and/or perimeter of neighbouring plaques, such differential hyper-reactivity in samples from AD patients, as well as in those with normal aging, seems to depend partially on the regional location of the involved astrocyte.

A radioligand-binding assay for detecting antibodies specific for proinsulin and insulin using 35S-proinsulin.

A new radioligand-binding assay (RBA) is described for the detection of insulin/proinsulin-specific antibodies using 35S-labeled proinsulin produced by a cell-free reticulocyte extract. Direct use of the crude expression product in the RBA was not feasible because the protein failed to fold properly (or had incorrectly paired disulphide bridges) and purification was hindered by interfering by-products. A refolding protocol and a chromatographic procedure were devised that readily allowed production of purified and immunochemically competent 35S-labeled proinsulin. The new RBA was compared with the reference test, in which the tracer was standard 125I-insulin. The analysis included sera from 41 diabetic patients and 25 healthy controls. Twenty-six (63.4%) and 29 (70.7%) patients scored positive by RBA using 35S-PI and 125I-insulin, respectively. The methods showed a satisfactory correlation with r(2)=0.77 and a slope not significantly different from unity (m=1.16+/-0.10; 95% confidence interval). Since the nuclide used in the assay is 35S, the procedure is compatible with standard assays for GADA and IA-2A, and thus may permit combined assays for the major early markers of autoimmune diabetes.

Immunochemical expression of proliferative cell nuclear antigen in aging cultured astrocytes.

Cell differentiation degree and mitotic activity were sequentially assessed by immunoperoxidase labeling of glial fibrillary acidic protein (GFAP) and proliferative cell nuclear antigen (PCNA), respectively, in rat brain cultured astrocytes maintained up to 60 days in vitro (DIV) of first subculture, or weekly passaged until their 12th subculture. Cell count was performed through a 0.01 mm2 section reticule and morphometric analysis with a stereological grid. The number of double immunoreactive cells peaked by 2 DIV to achieve its lowest value at 60 DIV. At 24 hs of cell seeding of successive passages, such values peaked by the 6th subculture to gradually decrease thereafter. Increasing cell hypertrophy was found during the long-term first subculture but not after passaging. At the end of the observation period, doubly immunolabeled astrocytes were still recorded, thus evidencing retention of proliferative potential despite aging.

Characterization of insulin antibodies by Surface Plasmon Resonance in two clinical cases: brittle diabetes and insulin autoimmune syndrome.

In this study, the characterization of insulin (auto)antibodies has been described, mainly in terms of concentration (q), affinity (Ka) and Ig (sub)isotypes by Surface Plasmon Resonance (SPR) in two particular clinical cases of individuals with severe episodes of impaired glycemia. Subject 1 suffers from brittle diabetes associated with circulating insulin antibodies (IA) due to insulin treatment. Subject 2 has insulin autoantibodies (IAA) associated with hypoglycemia in spite of not being diabetic and not having ever received exogenous insulin therapy. After conventional screening for IA/IAA by radioligand binding assay (RBA), we further characterized IA/IAA in sera of both patients in terms of concentration (q), affinity (Ka) and Ig (sub)isotypes by means of SPR technology. In both cases, q values were higher and Ka values were lower than those obtained in type 1 diabetic patients, suggesting that IA/IAA:insulin immunocomplexes could be responsible for the uncontrolled glycemia. Moreover, subject 1 had a predominat IgG1 response and subject 2 had an IgG3 response. In conclusion, SPR technology is useful for the complete characterization of IA/IAA which can be used in special cases where the simple positive/negative determination is not enough to achieve a detailed description of the disease fisiopathology.

Surface plasmon resonance reveals a different pattern of proinsulin autoantibodies concentration and affinity in diabetic patients.

Type 1 diabetes mellitus (DM) is characterized by autoimmune aggression against pancreatic beta cells resulting in absolute deficiency of insulin secretion. The first detectable sign of emerging autoimmunity during the preclinical asymptomatic period is the appearance of diabetes-related autoantibodies. In children at risk for type 1 DM, high-affinity Insulin autoantibodies reactive to proinsulin, are associated with diabetes risk. Autoantibodies are usually measured by radioligand binding assay (RBA) that provides quasi-quantitative values reflecting potency (product between concentration and affinity) of specific autoantibodies. Aiming to improve the characterization of the specific humoral immune response, we selected surface plasmon resonance (SPR) as an alternative method to measure proinsulin autoantibodies (PAA). This novel technology has allowed real time detection of antibodies interaction and kinetic analysis. Herein, we have employed SPR to characterize the PAA present in sera from 28 childhood-onset (mean age 8.31±4.20) and 23 adult-onset diabetic patients (≥65 years old, BMI<30) in terms of concentration and affinity. When evaluating comparatively samples from both groups, childhood-onset diabetic patients presented lower PAA concentrations and higher affinities (median 67.12×10(-9) M and 3.50×10(7) M(-1), respectively) than the adults (median 167.4×10(-9) M and 0.84×10(7) M(-1), respectively). These results are consistent with those from the reference method RBA (Standard Deviation score median 9.49 for childhood-onset group and 5.04 for adult-onset group) where the binding can be directly related to the intrinsic affinity of the antibody, suggesting that there is a different etiopathogenic pathway between both types of clinical presentation of the disease. This technology has shown to be a useful tool for the characterization of PAAs parameters as an alternative to radioimmunoassay, with high versatility and reproducibility associated to low occupational and environmental risk. However, this technology is not eligible for routine marker screening, but this is a powerful technique for a fine description of the thermodynamic parameters of antigen-antibody interaction.

Detection and immunochemical characterization of glutamic acid decarboxylase autoantibodies in patients with autoimmune diabetes mellitus.

Since GAD65 undergoes post-translational processing and targeting to subcellular compartments and membranes, it may exhibit different immunochemical properties in the cell context compared with the soluble protein expressed in the cell-free eukaryotic system used in the reference method for GADA assessment (radioligand binding assay (RBA)). In the present work, we detected and characterized GADA in 72 sera from patients with type 1 diabetes mellitus (DM) and 14 sera from adult-onset diabetes patients using analytical systems in which GAD65 is expressed in a cellular context: confocal indirect immunofluorescence (IIF) and electron microscopy after immunogold labeling on monolayers of transfected Chinese hamster ovary (CHO) cells, and immunoprecipitation (IP) of metabolically labeled GAD65. Eighteen serum samples, 16 from type 1 diabetes patients and two from adult-onset diabetes patients, were positive by confocal IIF but scored negative by RBA. All of these 18 sera immunoprecipitated a 65 kDa protein, supporting the existence of the GADA marker in such patients. It may be concluded that GADA negativity by the conventional RBA method using the soluble antigen, as well as negativity for other common markers measured by similar methods, is not enough to rule out the existence of the specific autoimmune component in childhood or adult-onset diabetes. Other analytical methods based in a more physiological presentation of the autoantigen structure, as confocal IIF and IP, bring an extra support to assess the complete repertoire of specific autoantibodies to native-like and membrane-bound, or denatured, beta-cell antigens.

Single-tube test for autoantibodies to glutamic acid decarboxylase and proinsulin as first-line screening for autoimmunity in adult-onset diabetic patients.

The aim of this work was develop a new combined radioligand-binding assay (RBA-combi) for the rapid and simultaneous determination of two autoimmunity markers, GADA and PAA, known to be differentially distributed in young and in some adult diabetic patients. The methodology was applied to sera from 85 young type 1 and 98 adult-onset diabetic patients with different marker profiles and insulin requirements, and to 53 normal control sera. Among type 1 diabetes sera used as autoimmunity controls, 100% of those with at least one positive marker by single methods and 17.7% of those with double negative markers were positive by RBA-combi (RBA-combi+). Among sera from adult-onset diabetes, 100% of those PAA+ (GADA+ or GADA-), 92.3% of GADA+/PAA-, and 1.3% of GADA-/PAA- were RBA-combi+. In conclusion, the new RBA-combi allowed the simultaneous detection of GADA and PAA markers with acceptable performance. Moreover, 16 out of 18 (88.9%) of adult patients RBA-combi+ evolved to insulin requirement, suggesting that this test is a valuable tool for assessing autoimmune processes associated to future impairment of insulin secretion.

Regional differences in astrocyte activation in HIV-associated dementia

Since astrogliosis is a histological marker usually observed in HIV-associated dementia (HIV-D),we decided to investigate the potential relationship between the expression of glial fibrillary acidicprotein (GFAP) and the regional distribution of cells positive (+) for this specific marker of astrocyte activation.Histological sections of brain tissues obtained at necropsy from 5 HIV-D patients and 5 age-matched controlswithout history of neuropsychiatric illness were immunostained with peroxidase. Mean numbers of GFAP(+)astrocytes were significantly increased in entorhinal cortex, hippocampus and subcortical white matter of patients,but values in frontal cortex and basal ganglia were similar to those of controls. In contrast, surface density ofimmunoreactive GFAP was significantly increased in all tested brain areas from all patients, including unusuallyaffected regions such as entorhinal cortex and hippocampus. Therefore, such consistent finding of hypertrophicastrocytes, ranging from highest cell percentajes in subcortical white matter to lowest in basal ganglia indicatesthat quantification of surface density in GFAP (+) cells appears to be a more reliable approach to score gliosisthan the counting of their cell nuclei. Because astrocyte activation involves both protective and detrimental effectson adjacent neuronal subsets, the evidence of regional differences in this reactive potential highlights theimportance of accurately defining their contribution to the neuropathogenesis not only of HIV-D, but of a widerange of neurodegenerative disorders.

Diferencias regionales en la activación astrocitaria en demencia asociada a HIV. Siendo laastrogliosis un signo histológico habitualmente presente en demencia asociada a HIV, se investigóla eventual relación entre expresión de proteína gliofibrilar ácida (GFAP) y localización regional de células positivaspara ese marcador específico de la activación astrocitaria. Por inmunoperoxidasa, se procesaron cortes histológicosde tejidos cerebrales obtenidos por necropsia de 5 pacientes y 5 controles de edades similares pero sin antecedentesneuropsiquiátricos. Según los valores de las medias registrados por conteo de astrocitos GFAP(+) en pacientes,el número fue significativamente mayor en corteza entorrinal, hipocampo y sustancia blanca subcortical, mientrasque en corteza frontal y ganglios basales no se encontraron diferencias con controles. En cambio, la densidad desuperficie del material GFAP inmunorreactivo en pacientes estuvo significativamente aumentada en todas las áreascerebrales analizadas, incluso en regiones inusualmente afectadas, como corteza entorrinal e hipocampo. Entreesos astrocitos hipertróficos, el mayor porcentaje correspondió a sustancia blanca subcortical, y el menor a gangliosbasales. Cabe concluir que el constante hallazgo de agrandamiento astrocitario señala a la medida de la superficieinmuno-reactiva como mejor índice de activación celular que el conteo de núcleos de las células marcadas. Dadoslos reconocidos efectos de la astrogliosis sobre las subpoblaciones neuronales vecinas, la comprobadaregionalización de ese potencial reactivo destaca el interés de precisar su contribución en la neuropatogenia, tantode demencia asociada a HIV como de otras enfermedades neurodegenerativas.

Immunochemical expression of proliferative cell nuclear antigen in aging cultured astrocytes

Cell differentiation degree and mitotic activity were sequentially assessed by immunoperoxidase labeling of glial fibrillary acidic protein (GFAP) and proliferative cell nuclear antigen (PCNA), respectively, in rat brain cultured astrocytes maintained up to 60 days in vitro (DIV) of first subculture, or weekly passaged until their 12th subculture. Cell count was performed through a 0.01 mm2 section reticule and morphometric analysis with a stereological grid. The number of double immunoreactive cells peaked by 2 DIV to achieve its lowest value at 60 DIV. At 24 hs of cell seeding of successive passages, such values peaked by the 6th subculture to gradually decrease thereafter. Increasing cell hypertrophy was found during the long-term first subculture but not after passaging. At the end of the observation period, doubly immunolabeled astrocytes were still recorded, thus evidencing retention of proliferative potential despite aging

Immunologic and genetic markers in insulin-dependent diabetes mellitus (Type 1) in a argentine population

The objective was to evaluate the prevalence and association of several markers (islet cell antibodies: ICA, ainsulin autoantibodies: IAA, glutamic acid decarboxylase antibodies: GADA and ICA512 antibodies: ICA512A) along with HLA DQB1 genotype in type 1 diabetes mellitus of recent onset, including siblings and individuals without any history of this disease, in an Argentine population. A total of 79 children with type 1 diabetes mellitus of recent onset were studied, as well as 79 control children, and 68 healthy siblings of type 1 diabetic cases. IAA, ICA, GADA, ICA512A and HLA DQB1 alleles were determined. Sensitivity was 67.1 por ciento for ICA, 36.7 percent for IAA, 74.6 por ciento for GADA and 63.4 por ciento ICA512A. None of the control subjects was positive for the immunological markers. Combined sensitivity of ICA-IAA-GADA was 89.8 por ciento, similar to the ICA512A- GADA (87.3 percent) or ICA512A-GADA-IAA combination (91.1 por ciento ). GADA correlated positively with ICA, but no such correlation was found between IAA, ICA512A and ICA. IAA correlated negatively and GADA positively with age. IAA was associated to DQB1*0201, whereas ICA and ICA512A associated to DQB1*0302. Among siblings, 3/68 (4.4 percent) were positive for IAA and a single case (1.5 percent) was positive for GADA and one for ICA512A. Our findings show that the combination of multiple tests increases the sensitivity for prediction, with the ICA512A-GADA combination proving highly sensitive and equivalent to other proposed combinations, such as ICA-IAA-GADA.

A quantitative approach to correlate astrocyte differentiation and phagocytic activity

A triple staining procedure (PAP labeling for GFAP, PAS reaction for added yeast cells and hematoxylin for nuclear staining of the whole cell monolayer) had disclosed that Junin virus infection enhanced phagocytic activity by inducing greater astrocyte differentiation. Here, we resorted to a mathematical approach for simultaneous evaluation of astrocyte differentiation and potential phagocytosis. At light microscopy level, the total number of: a) PAS-stained yeast cells, b) PAS-stained yeast cells associated to GFAP-positive astrocytes, c) GFAP-positive astrocytes, and d) total number of GFAP-labeled and non-labeled astrocytes, were counted within the monolayer area delimited by a grid with a total area of 0.01 mm2. As the percentage of PAS-stained yeast cells associated to GFAP-positive astrocytes correlated significantly with the percentage of GFAP-positive astrocytes for the three yeast cell incubation times (24, 48 and 72 h), a mathematical approach involving a so-called beta parameter representing the percentage of differentiated astrocytes capable of taking up 50 of added yeast cells, was developed. Since beta value dropped along yeast cell incubation time, and more markedly in Junin-virus infected samples, a numerical value was thus available to assess enhanced phagocytic activity in astrocytes undergoing differentiation. Therefore, the application of a mathematical approach to cell monolayers subjected to current staining techniques, allows more objective analysis of data provided by cursory visualization at light microscopy level.

Cell differentiation increases astrocyte phagocytic activity: a quantitative analysis of both GFAP labeling and pas-stained yeast cells

Since efficiency of phagocytic potential in activated astrocytes is still a subject of controversy, an attempt was made to quantify simultaneously phagocytic activity and astrocyte differentiation. Resorting to Junin virus, known to induce astrocyte activation, infected vs control samples of cultured rat astroglial cells were serially harvested up to day 12 post-inoculation (pi), and subjected to a triple staining procedure consisting in immunoperoxidase labeling of GFAP, periodic acid-Schiff (PAS) reaction in added baker's yeast cells and hematoxylin for nuclear staining of the whole cell monolayer. Adopting GFAP labeling as a specific marker of astrocyte differentiation, the immunoprecipitate development over time was measured. Direct calculation of the initial reaction rate was feasible given its linear behavior during the first 10 min, so that GFAP amount was regarded proportional to peroxidase activity. As determined by digital image analysis, mean optical density (MOD) values of GFAP in infected samples increased from 0.618 + 0.082 at day 1 pi to 0.825 + 0.125 at day 3, leveling off at 1.010 + 0.101 as from day 9, while control unifected samples remained unchanged at roughly 0.6 during the entire observation period. In turn, phagocytosis was quantified by PAS staing densitometry, whose intensity varied according to wall degradation of yeast cells. MOD levels of PAS-stained phagocytized yeast cells were significantly lower (p <0.05) in efected vs control cultures at 48 and 72 h following their addition to the astroglial monolayer. According to simultaneous quantification of two components of astrocyte response to viral infection, it is concluded that phagocytic activity increases with astrocyte differentiation.

Marcadores inmunológicos y genéticos en diabetes mellitus tipo 1 en Argentina / Immunologic and genetic markers in type 1 diabetes mellitus in Argentina

El objetivo del trabajo fue evaluar la prevalencia y asociación de los marcadores inmunológicos (anticuerpo anti-islote pancreático: ICA, autoanticuerpo anti-insulina: IAA, anticuerpo antidecarboxilasa del ácido glutámico: GADA y anticuerpo anti ICA512) y con el genotipo HLA DQBl en pacientes con diabetes tipo 1 de reciente debut, hermanos de diabéticos y personas sin historia de enfermedad autoinmune en población argentina. Se estudiaron 79 niños con diabetes tipo 1 de reciente debut, 79 niños controles y 68 hermanos sanos de niños con diabetes 1. En todos ellos se determinó IAA, GADA, ICA, ICA512 y alelos HLA DQB1. La sensibilidad para ICA fue de 67.1 por ciento; para IAA de 36,7 por ciento; para GADA de 74,6 por ciento, y para ICA512 de 63,4 por ciento. Ninguno de los niños control presentó marcadores inmunológicos positivos. La sensibilidad combinada de ICA-IAA-GADA fue de 89,8 por ciento, similar a la de ICA512-GADA (87.3 por ciento) o la combinación de ICA512-GADA-IAA (91.1 por ciento). El valor de GADA presentó correlación positiva con el de ICA, no encontrándose correlación alguna entre los valores de IAA, ICA512 e ICA. El valor de IAA presentó correlación negativa y el de GADA positiva con la edad de los pacientes. La presencia de IAA se asoció con DQB1 *0201, mientras que la de ICA e ICA512 con DQB1 *0302. Entre los hermanos, 3/68 (4,4 por ciento) fueron positivos para IAA, uno (1,5 por ciento) lo fue para GADA y otro (1.5 por ciento) para ICA512. Nuestros resultados muestran que la combinación de múltiples marcadores incrementa la sensibilidad predictiva, siendo la asociación ICA512-GADA altamente sensible y equivalente a otras combinaciones propuestas como ICA-IAA-GADA