Innate recognition of bacteria: engagement of multiple receptors

Until recently, consensus was that the mechanism of action of the innate immune system was a simplified one. Current research findings in the field of innate recognition of bacteria suggest that it involves complex associations of receptors depending on cell type and bacterial stimuli, CD14, integrins, Toll-like receptors (TLRs), CD55, ion channels, and activation clusters containing heat shock proteins, chemokine receptor 4 and a plethora of other molecules have been shown to serve as key molecules in bacterial recognition. In this article, we review all the advances in the field and discuss the possibility that the repertoire for recognition of pathogens is defined by the combinational engagement of multiple receptors.     

Activation of mouse complement by different classes of mouse antibody.

The capacity of mouse IgM, IgGl, IgG2 and IgA anti-dinitrophenyl (DNP) antibodies to activate mouse or guinea-pig complement was studied, using a sensitive haemolytic assay and two-dimensional immunoelectrophoresis to detect cleavage of mouse C3. Three monoclonal IgM antibodies, and a heterogeneous IgM fraction, lysed trinitrophenylated erythrocytes in the presence of guinea-pig C, but failed to produce lysis in the presence of mouse C. and only activated mouse C3 very inefficiently. A monoclonal IgGl antibody did not produce haemolysis in the presence of guinea-pig or mouse C, but cleaved mouse C3 via the alternative pathway. Two IgA myeloma proteins (M315 and M460) had similar properties. A heterogeneous IgG2 antibody fraction produced haemolysis in the presence of both mouse and guinea-pig C, and was shown to activate both the classical and alternative pathways of mouse C.     

Interaction of PSD-95 with potassium channels visualized by fluorescence lifetime-based resonance energy transfer imaging

Resonance energy transfer (RET) has been extensively used to estimate the distance between two different fluorophores. This study demonstrates how protein-protein interactions can be visualized and quantified in living cells by time-correlated single-photon counting (TCSPC) imaging techniques that exploit the RET between appropriate fluorescent labels. We used this method to investigate the association of the potassium inward rectifier channel Kir2.1 and the neuronal PDZ protein PSD-95, which has been implicated in subcellular targeting and clustering of ion channels. Our data show that the two proteins not only colocalize within clusters but also interact with each other. Moreover, the data allow a spatially resolved quantification of this protein-protein interaction with respect to the relative number and the proximity between interacting molecules. Depending on the subcellular localization, a fraction of 20 to 60% of PSD-95 molecules interacted with Kir2.1 channels, approximating their fluorescent labels by less than 5 nm.     

Blinded, Externally Controlled Multicenter Evaluation of Light Microscopy and PCR for Detection of Microsporidia in Stool Specimens

The quality parameters for the detection of microsporidia in identical sets of 50 stool samples were determined for six laboratories where technicians used light microscopy and for six laboratories where technicians used PCR. The average overall sensitivities were 67% (89% for patient samples only) for the PCR laboratories and 54% (80% for patient samples only) for the light microscopy laboratories. Specificities were 98 and 95%, respectively. Differences in results were most apparent between the individual laboratories rather than between the two major methods used.