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Serological responses of Icelandic sheep experimentally infected with visna virus (vv) were contrasted with responses in American Targhee sheep naturally infected with progressive pneumonia virus (ppv). Precipitating antibodies assayed by immunodiffusion were compared with the neutralising and complementing fixing antibody response. In experimental infections with vv, complement fixing and neutralising antibodies appeared early after infection and rose to high levels in all sheep, while precipitating antibodies were detected only at minimal titre. In natural infections with ppv, immune responses were less consistent and precipitating antibodies were detected more frequently than complement fixing or neutralising antibodies against ppv. These results may suggest important biological differences between the lytic fibroblast-tropic virus strains used for experimental infection of Icelandic sheep and the nonlytic macrophage-tropic strains of ppv circulating in nature. Lytic strains evoke a brisk response against the viral glycoprotein with high titre neutralising antibody while nonlytic strains induce a less consistent response to the glycoprotein.

A small set of concanavalin A (Con A)-binding glycoproteins was isolated from the surface membrane of cloned cytotoxic T lymphocytes (CTL) and partly identified using monoclonal antibodies. The binding of Con A by these glycoproteins on the CTL surface results in the secretion of gamma-interferon and in blocking the effector functions of the cells-namely, antigen-specific and lectin-dependent cytotoxicity. The Con A is evidently bound tightly to some surface structures ("Con A-receptors") that are required for the activation and cytotoxic activity of CTL. To isolate and identify these receptors, antibodies to Con A were used. After Con A was allowed to bind to radiolabeled cloned CTL (labeled with 125I or [35S]methionine or 3H-labeled amino acids), the cells were washed thoroughly, lysed in detergents and anti-Con A antibodies were added to bind to the Con A-receptor complexes. The resulting aggregates were adsorbed with protein A-bearing Staphylococci and the receptors were then specifically released from the pelleted bacteria by alpha-methyl-D-mannoside and analyzed by polyacrylamide gel electrophoresis under reducing conditions. Eight to nine labeled components were seen by autoradiography and with the aid of monoclonal antibodies to known T-cell surface molecules, four were identified as T200, lymphocyte function-associated antigen (LFA)-1, alpha- and beta-chains, and (on some clones) Lyt-2. Other components with Mr congruent to 160,000, 120,000, 46,000, 42,000, and 23,000 have not been identified. The procedures described here may have general application in the studies of the functional properties of other cell surface molecules.

Interferon (IFN) was found to be secreted by cloned lines of murine cytotoxic T lymphocytes in response to mitogenic or antigen specific stimulation. The IFN produced was shown to be of the immune type based on its sensitivity to pH 2.0 and on the ability of an antiserum to immune IFN to neutralize the antiviral activity.

A specimen of brain from a patient with fatal encephalitis was prepared for inoculation into tissue-culture monolayer systems by dispersal of cells with trypsin diluted in saline and by homogenization with mortar and pestle. In primary isolations and in reisolations from the original materials, Herpesvirus hominis (HVH) was recovered from 24 of 31 cell cultures inoculated with trypsindispersed brain cells and from none of 32 cultures inoculated with brain homogenate. Inoculation of tissue-culture systems with intact, infected cells appears to be a more sensitive method of recovering the agent from patients with HVH encephalitis than inoculation of homogenized tissue; thus this method should be evaluated further.

Persistent virus, infections present a paradox; there exists a potent array of antiviral immune defenses, and yet there are many naturally occurring instances of persistent virus infection in animals and in humans. In this short review we will examine the diverse strategies whereby persistent viruses escape immune surveillance, and illustrate these mechanisms by reference to a few selected examples. More detailed information is available in a number of symposia and compendia (1–5).

Icelandic sheep were injected intracerebrally with visna virus, which produces a persistent infection of the CNS accompanied by encephalomyelitis and focal demyelinating lesions. Studies were conducted on two groups of sheep, with short-term infections (25 sheep sampled 1–3 months after infection) and long-term infections (14 sheep sampled 5–6 years after infection). Quantitative determination of CSF immunoglobulin levels 5 years after infection indicated that IgM concentrations was usually elevated, IgG2 was occasionally elevated and IgG1 was rarely elevated. CSF oligoclonal bands were seen in about half the sheep examined 5 years after infection. There was a correlation between high titers of CSF antiviral antibody and both elevated CSF IgM concentration and CSF oligoclonal bands. Serum/CSF IgG1 ratios indicated that the blood-brain barrier was apparently intact in long-term visna infection, consistent with intrathecal synthesis of IgM and of antiviral antibody. The alterations in CSF immunoglobulins in visna resemble those found in other persistent CNS virus infections and in multiple sclerosis.

Two Icelandic sheep with clinical signs of visna appearing 6-7 years after intracerebral infection with visna virus were killed, fixed by perfusion and the central nervous system lesions examined by light and electron microscopy. Both sheep showed similar pathological changes. In the brain there was a severe periventricular inflammatory process with small foci of liquefaction necrosis and scattered small granulomas. In some areas of inflammation there was evidence of primary demyelination but it was not prominent. In the spinal cord there were focal plaques of primary demyelination. At the ultrastructural level the spinal cord lesions showed unambiguous primary demyelination with many naked axons; various stages of remyelination with peripheral type of myelin were also common. These observations indicate that the CNS lesions of visna, as seen in Icelandic sheep, fall into two categories: (a) an inflammatory process which often begins within weeks of infection and which occurs in the majority of infected animals in the absence of clinical paresis; and (b) focal demyelinating lesions of the spinal cord which are seen in sheep with clinical paresis but are uncommon in animals prior to onset of clinical signs. Both types of lesions may coexist.

This screening model framework is intended to provide a preliminary assessment of hydrodynamic and/or water quality behavior within an estuary. Since the model is diagnostically designed, it can readily incorporate available information; its generic structure allows application to any system. Another characteristic, the kinematic formulation of current fields, provides an alternative to the formidable task of solving a full set of geophysical, fluid-dynamics equations. Hydrodynamic features, either known or postulated, can thus be incorporated through appropriate boundary conditions. The model is steady-state, two-dimensional, depth-averaged and uses a finite element solution technique. The model was applied to Breton Sound (Louisiana) to investigate the significance of gross circulation features and the possible effects of a proposed fresh water diversion on salinity distributions. The results contributed to the formulation of a field monitoring program to support the development of an eventual real-time modeling application that will be used in determining an operating schedule for the diversion structure. The results, as presented, demonstrate the utility of the modeling framework for identifying processes, controlling circulation, future research needs, and appropriate follow-up modeling approaches.

A case is presented of mitral and aortic valvular insufficiency due to myxomatous valvular transformation. Unusually long chordae tendineae were found to be inserted either directly into the endocardium or into flattened papillary muscle. In addition, a thin "sail"-shaped subaortic membrane was present. Myxomatous valvular degeneration should be considered in the differential diagnosis of valvular insufficiency, even in the absence of stigmata of other disease processes.

Experiments to heat a simulated propellant to high bulk temperatures by the absorption of thermal radiation are discussed. Argon seeded with micron-sized carbon particles was used as the simulated propellant; a 500 kw d-c arc was used as the radiant energy source. Bulk temperatures up to 3860 K were obtained with greater than 95% of the incident radiation absorbed. The arc radiation source, seed dispersal equipment, techniques used to prevent transparent wall coating by the seeds, and calorimetric measurement of bulk temperature are also discussed.

The progress in steganography is hampered by a gap between non-additive distortion functions, which capture well complex dependencies in natural images, and their additive counterparts, which are efficient for data embedding. This paper proposes a theoretically justified method to approximate the former by the latter. The proposed method, called Backpack (for BACKPropagable AttaCK), combines new results in the approximation of gradients of discrete distributions with a gradient of implicit functions in order to derive a gradient w.r.t. the distortion of each JPEG coefficient. Backpack combined with the min max iterative protocol leads to a very secure steganographic algorithm. For example, the error rate of XuNet on 512 X 512 JPEG images, compressed with quality factor 100 and a payload of 0.4 bits per non-zero AC coefficient is 37.3% with Backpack, compared to a 26.5% error rate using ADV-EMB with minmax (considered state of the art in this work) and a 16.9% error rate with J-UNIWARD.