Cooperation of BMP and IHH signaling in interdigital cell fate determination.

The elaborate anatomy of hands and feet is shaped by coordinated formation of digits and regression of the interdigital mesenchyme (IM). A failure of this process causes persistence of interdigital webbing and consequently cutaneous syndactyly. Bone morphogenetic proteins (BMPs) are key inductive factors for interdigital cell death (ICD) in vivo. NOGGIN (NOG) is a major BMP antagonist that can interfere with BMP-induced ICD when applied exogenously, but its in vivo role in this process is unknown. We investigated the physiological role of NOG in ICD and found that Noggin null mice display cutaneous syndactyly and impaired interdigital mesenchyme specification. Failure of webbing regression was caused by lack of cell cycle exit and interdigital apoptosis. Unexpectedly, Noggin null mutants also exhibit increased Indian hedgehog (Ihh) expression within cartilage condensations that leads to aberrant extension of IHH downstream signaling into the interdigital mesenchyme. A converse phenotype with increased apoptosis and reduced cell proliferation was found in the interdigital mesenchyme of Ihh mutant embryos. Our data point towards a novel role for NOG in balancing Ihh expression in the digits impinging on digit-interdigit cross talk. This suggests a so far unrecognized physiological role for IHH in interdigital webbing biology.

The expression of NKG2D on porcine IEL and its possible relation to the adaptive intestinal immune system.

The gastrointestinal tract contains a multitude of components which include intraepithelial lymphocytes (IEL). IELs have been reported to express a variety of surface receptors that enable cross talk among various cell populations. The purpose of the reported investigation was to determine which IEL populations express the natural killer cell receptor NKG2D which is an activating receptor that plays a role in cytolytic responses. In a feeding experiment with piglets, IELs were isolated from jejunal tissue at three different stages post weaning. The time dependent development of different cell populations was evaluated and an elevated number of lymphocytes (CD45+) shortly after weaning was observed compared to later time points. The number of T cells (CD3), including cytotoxic T cells (CD8ß/CD16-), appeared to be particularly affected by the weaning period. Correlation analysis revealed an association between the NKG2D expression in jejunal tissue and the frequency of lymphocytes, esp. CD8ß+ cytotoxic T cells. Gene expression analysis of NKG2D were performed on several isolated IEL populations and support the hypothesis that cytotoxic T cells (CD8ß) in the porcine gut epithelium are capable of communicating with the surrounding enterocytes and inducing immune reactions via NKG2D. Unlike previous observations in porcine blood, the γδ T cells of the gut epithelium also showed expression of the stress factor binding NKG2D receptor. Subsequent analysis of the isolated IELs revealed that T cells appear to only express the receptor after isolation with an anti-CD3 mab, indicating that a previous stimulation of the TCR/CD3 complex may reinforce this signal transduction pathway.

Impact of a probiotic Bacillus cereus strain on the jejunal epithelial barrier and on the NKG2D expressing immune cells during the weaning phase of piglets.

In a feeding experiment, the probiotic Bacillus cereus var. Toyoi was fed to sows and piglets in order to test whether it influences the stress response of enterocytes, thereby causing intestinal immune activation, possibly accompanied by an impairment of the epithelial integrity. The impact of B. cereus on the piglets' intestinal enterocytes (EC) and on the communicating intraepithelial lymphocytes (IEL) was investigated during the weaning phase where significant immunological changes might be expected. The expression of the stress-induced MHC class I-related molecule 2 (MIC2) and the UL16 binding protein (ULBP) was measured in jejunal EC and the frequencies of the main present IEL populations in the jejunum were monitored. To find out which of the IEL populations can be activated by the stress-induced molecules the sorted IEL were tested for the expression of the activating natural killer receptor 2D (NKG2D). The piglets fed with B. cereus showed an impaired intestinal barrier function shortly after weaning. However, a significant impact on the expression of stress-induced molecules was not observed. The mRNA expression of NKG2D was confirmed in intraepithelial CD5+ γδ T cells. The ratio of IEL (CD45+) to EC was lower in the B. cereus treated group, which could be explained by lower frequencies of CD8αß+ T cells in the jejunal epithelium (p ≤ 0.005 for ages 32 and 34). Although a consistently increased expression of stress-induced MHC class I-related molecules was not found, this study suggests a negative impact of B. cereus on the intestinal barrier function and supports immune-modulating properties of the probiotic feed supplement.