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Downregulation of MHC class I molecules is a strategy developed by some viruses to escape cellular immune responses. Myxoma virus (MV), a poxvirus causing rabbit myxomatosis, encodes MV-LAP that is known to increase MHC-I endocytosis and degradation through a C(4)HC(3) motif critical for an E3 ubiquitin ligase activity. Here, we performed a functional mapping of MV-LAP and showed that not only the C(4)HC(3) motif is necessary for a marked downregulation of MHC-I but also a conserved region in the C-terminal part of the protein. We also showed that the putative transmembrane domains are responsible for a specific subcellular localization of the protein: they retain MV-LAP in the ER in transfected cells and in the endolysosomal compartments in infected cells. We observed that a specific MV infection context is necessary for a fully efficient downregulation of MHC-I. Our data suggest that the functionality of viral LAP factors, inherited by herpes- and poxviruses from mammalian cells, is more complex than anticipated.

Allergy to Hymenoptera venom (VH) effects more and more patients in France. It is manifest in two main forms, which are Loco-regional (RLR) and Systemic reactions (SR). This allergy is detectable amongst others by the techniques of histamine release (HR) and release of leucotrienes C4 (LTC4). The aim of this work has been to fix a threshold that gives differentiation of RLR ad RS by the two techniques. We found in a positive population a threshold histamine release (HR) value of 25% and a concentration of LTC4 of 600 ng/ml. These are the thresholds above which a patient would be at around 70% risk of RS. This study has a predictive value for patients who are suspected of allergy of VH or who have already had clinical reactions and risk sensitization.

The haemolytic activity of Streptococcus equi, the cause of equine strangles, was characterized. Production of haemolysin in Todd Hewitt broth was dependent on an equine serum supplement and the logarithmic phase of growth after which activity declined sharply. RNA core also induced haemolysin production from cells harvested at the end of the logarithmic phase of growth. Haemolysis was not affected by cholesterol, was only slightly increased in reducing conditions and was completely inactivated by trypan blue, identifying the haemolytic activity as streptolysin S-like (SLS-like). Purification by hydroxyapatite and Sephacryl column chromatography yielded proteins of molecular weights of approximately 6000 and 17 000-22 000 Da with a 64-fold increase in specific activity. Low molecular weight proteins from the RNA core were still present in the purified toxin. Two non-haemolytic mutants were derived by conjugation with an Enterococcus faecalis-carrying transposon Tn916. Southern blots of HindIII digests of DNA revealed that one of the mutants contained three transposon insertions and the other just one. A lambda phage library of S. equi contained plaques whose haemolytic activity was enhanced by reducing conditions and inhibited by cholesterol, suggesting a streptolysin O-like (SLO-like) activity. However, haemolysin in culture sonicates of host E. coli in which the lambda phage insert was subcloned into plasmid (pUC18), was not affected by these conditions. Seven isolates of S. equi in medium without SLS-like inducers showed no SLO-like activity and no evidence for an SLO-like toxin could be found by immunoblotting with pneumolysin antiserum and monoclonal antibodies or by polymerase chain reaction with primers derived from sequences conserved between the SLO genes of Lancefield group A, C and G streptococci. S. equi does not appear to possess a streptolysin O but does make a streptolysin S-like toxin whose production can be interrupted at just one genetic locus., (Copyright 1998 Academic Press Limited.)

Rhesus monkeys were tested on a visual search task in which they had to find and retrieve a peanut from a display of visually similar but inedible objects. The speed with which they did so was measured. Animals in which the superior colliculi or frontal eye-fields had been removed took longer to find the peanut than two operated control groups. Animals with collicular lesions had longer latencies than those with frontal eye-fields removed. These two groups were also tested on a second task, non-visual search, in which a peanut was concealed in each of 25 identical holes. The animals' task was to retrieve all 25 peanuts as quickly as possible. The group with frontal eye-fields removed made significantly more return errors, i.e. returning to a hole already sampled, than the control group but, in contrast to the first task, the animals with collicular lesions were not impaired. The results are related to the physiological properties of frontal eye-fields and superior colliculi and to the effects of frontal cortical brain damage in man. It is suggested that the frontal eye-fields are concerned with internally organized, i.e. voluntary, eye scanning whereas the superior colliculi are concerned with the detection and location of targets which are then fixated involuntarily.