Medición de 25-hidroxivitamina D sérica: comparación de dos inmunoensayos / Measurement of 25-hydroxyvitamin D in serum: comparison of two immunoassays

La concentración sérica de 25-hidroxivitamina D (25-OHD) es utilizada como indicador del estado nutricional de Vitamina D (VD). El método más utilizado para medirla es el RIA. El desarrollo reciente de métodos automatizados no radiactivos facilitaría la práctica diaria de laboratorio y el diagnóstico de necesidad de suplementación. Objetivos: Comparar los datos de 25-OHD obtenidos usando un RIA y un método de quimioluminiscencia (QLIA) automatizado disponible en nuestro medio. Materiales y métodos: Concentraciones de 25-OHD se midieron en suero de 45 pacientes: 8 hombres y 37 mujeres; 18 no suplementados y 27 suplementados con VD (n=5 con VD2 y n=22 con VD3). Las mediciones de 25-OHD se realizaron con un RIA y un QLIA automatizado (LIAISON), ambos DiaSorin. Se calcularon los coeficientes de variación intraensayo (CV intra) e interensayo (CV inter) para ambos métodos. Análisis estadístico: la comparación entre métodos se realizó con los programas Analyse-it y Med Calc Se consideró significativa una p<0.05. Resultados: Los CV% intra e inter fueron: para RIA menores de 10,6 y 19,9 vs QLIA menores de 8,0 y 13.2, respectivamente. En la población total y en el subgrupo no suplementado con VD los datos de RIA vs QLIA fueron: coeficiente de correlación de Pearson (0,9259 vs 0,9412), Bias%: (6.1 vs 2.7), coeficiente de concordancia (0,9244 vs 0,9329). Conclusiones: 1) Ambas metodologías son adecuadas para mediciones de 25OHD, especialmente en casos no medicados con VD, 2) La tendencia hacia un mayor bias% observado en pacientes suplementados con VD no parecería ser atribuible a variabilidad metodológica, y sugeriría que la VD exógena o alguno de sus metabolitos interactuaría en forma diferente en la medición de 25-OHD por cada una de las metodologías utilizadas. Mayor número de casos es necesario a fin de confirmar esta hipótesis.

Serum concentration of 25-hydroxyvitamin D (25OHD) is used as an indicator of nutritional status of Vitamin D (VD). The methodolgy more frequently used for its measurement is RIA. The recent development of automated non-radioactive methodologies would help the laboratory daily practice to diagnose the need for supplementation. Objectives: To compare the data of 25-OHD obtained using a RIA and an automated chemiluminescence method (CLIA) automated available in our country. Materials and methods: Concentrations of 25-OHD were measured in serum of 45 patients: 8 men and 37 women, 18 unsupplemented and 27 supplemented with VD (n=5 with VD2 and n=22 with VD3). For 25-OHD measurements we used a RIA and a QLIA under an automated platform (LIAISON), both DiaSorin. We calculated intra-assay (intra) and interassay (inter) coefficients of variation (CV%) for both methods. Statistical analysis: comparison between methods was conducted with Analyse-it and Med Calc softwares; p <0.05 was considered significant. Results: The intra and inter CV% were below 19.9 and 10.6 for RIA vs 8.0 and 13.2 for CLIA, respectively. In the overall population and in the subgroup never supplemented with VD, data for RIA vs CLIA were: Pearson correlation coefficient (0.9259 vs 0.9412), Bias% (6.1 vs. 2.7), concordance coefficient (0.9244 vs 0.9329). Conclusions: 1) Both methods are suitable for measurements of 25OHD, particularly in cases not medicated with VD, 2) The trend toward greater bias% observed in patients supplemented with VD does not appear to be attributable to methodological variability, and suggests that exogenous VD or its metabolites interact differently in the measurement of 25-OHD by each of the methodologies used. A higher number of cases is needed to confirm this hypothesis.

Interaction of bifidobacteria with the gut and their influence in the immune function

Bifidobacteria are predominant in the lumen of the large intestine and confer various health benefits on the host. They are also used in the preparation of new fermented milks (bioyogurts) or added to conventional yogurt to generate probiotic effects. The colonization of the gut by bacteria tends to be host specific due partly to the way in which bacteria adhere to the intestinal wall. Using a homologous strain of Bifidobacterium animalis in an experimental mouse model, we analyzed by immunofluorescence labelled-bacteria and transmission electronic microscopy the importance of the bacterial interaction with epithelial an immune cells associated to the gut, and the effect of feeding of B. animalis in the immune response. It was able to adhere and interact with both small and large intestine. In spite of this interaction with the gut, no modifications in the immune state (secretory or systemic response) were observed. A heterologous strain of Bifidobacterium adolescentis from human faeces, was neither incapable of binding to the intestine, nor influence the immune system activation, when it was administered during 2, 5 or 7 consecutive days; we believe that using a homologous strain, oral tolerance is developed even when the microorganism interacts with the immune cells associated with the intestine. However, we cannot ignore the beneficial effect of these microorganisms, especially in the prevention of intestinal infections. We think that this property exerted by bifidobacteria is more related to other mechanisms such as competitive inhibition, acid production or others, than enhancement of the immune state.

Infección por citomegalovirus en el adulto sano: ¿tiene mi paciente una infección activa? ¿es ésta responsable de su cuadro clínico? / Cytomegalovirus infection in healthy adults: does my patient have an active infection? Is that infection the cause of the patient's clinical pattern?

La infección por citomegalovirus (CMV) tiene una alta incidencia aunque generalmente cursa en forma asintomática, siendo el síndrome mononucleósido el cuadro clínico que más frecuentemente se observa en la enfermedad sintomática del adulto sano. Ocasionalmente se observan otras manifestaciones que son raras en el adulto sano y menos expresiva clínicamente que en el inmunodeprimido, por lo que deben llevar a la búsqueda de un factor de inmunodepresión, y a ser cuidadoso en concluir la relación causal. La interpretación de la serología clásica ofrece dificultades por lo que proponemos un algoritmo que permita salvarlas, y analizaremos el concepto de avidez, que si bien esta técnica aún no está disponible en nuestro medio , permitirá resolver la mayoría de estos problemas. También analizamos el rol diagnóstico de la técnica de PCR en el inmunocompetente. Finalmente, dada la alta incidencia de la infección por CMV, aunque la serología muestra evidencias de infección activa, esta no necesariamente es responsable del cuadro clínico en curso, pudiendo ser un hecho concomitante a otra enfermedad, incluso una reactivación debida a la inmunodepresión causada por esa otra enfermedad. La certeza diagnóstica la brinda la demostración histológica de la infección. Dado que la enfermedad por CMV en el adulto sano tiene habitualmente una evolución benigna, no requiriendo un tratamiento antiviral específico, generalmente no es necesaria la demostración histológica. En los cuadros atípicos se plantean diagnósticos diferenciales que tienen implicancia pronósticas y terapéuticas, por lo que en algunos casos se debe recurrir a técnicas diagnósticas invasivas para obtener muestras histológicas

Gut mucosal immunostimulation by lactic acid bacteria

The beneficial properties of lactic acid bacteria (LAB) on human health have been frequently demonstrated. The interaction of LAB with the lymphoid cells associated to the gut to activate the mucosal immune system and the mechanisms by which they can exert an adjuvant effect is still unclear, as well as if this property is common for all the LAB. We studied the influence of the oral administration of different geneous of LAB such as Lactobacillus casei, L. acidophilus, L. rhamnosus, L. delbrueckii subsp. bulgaricus, L. plantarum, Lactococcus lactis and Streptococcus thermophilus. We determined if the LAB assayed were able to stimulate the specific, the non-specific immune response (inflammatory response), or both. We demonstrated that all the bacteria assayed were able to increase the number of IgA producing cells associated to the lamina propria of small intestine. This effect was dose dependent. The increase in IgA+ producing cells was not always correlated with an increase in the CD4+ T cell number, indicating that some LAB assayed only induced clonal expansion of B cells triggered to produce IgA. Most of them, induced an increase in the number of cells involved in the inflammatory immune response. CD8+ T cell were diminished or not affected, with exception of L. plantarum that induced an increase at low dose. This fact would mean that LAB are unable to induce cytotoxicity mechanisms. We demonstrated the importance in the selection of LAB to be used as gut mucosal adjuvant. The different behaviours observed among them on the gut mucosal immune response, specially those that induce inflammatory immune response, show that not all the LAB can be used as oral adjuvant and that the beneficial effect of them can not generalized to genous or specie. The immunoadjuvant capacity would be a property of the strain assayed.