Comparative efficacy of 5-methoxymethyl-2'-deoxyuridine, 9 beta-D-arabinofuranosyladenine and 5-iodo-2'-deoxyuridine in the treatment of experimental herpes simplex keratitis

The relative efficacy of 5-methoxymethyldeoxyuridine (MMUdR), adenine arabinoside (Ara-A), 5-iododeoxyuridine (IUdR) and the combination of MMUdR and Ara-A in the treatment of experimental herpes simplex keratitis was investigated in rabbits. Treatment was initiated either at 4 or 24 h post virus inoculation. The parameter used to evaluate effectiveness was lesion size. Each eye was graded daily for the first 5 days and on alternate days thereafter to day 11. At concentrations of 2 or 5% both MMUdR and Ara-A were found to have potent antikeratitis activity. At 5% concentration, Ara-A provided essentially the same protection against herpes keratitis as 0.1% IUdR, while MMUdR was slightly less effective. The simultaneous application of 2% MMUdR and 2% Ara-A in combination was more effective than 5% MMUdR alone and was effective as 5% Ara-A or 0.1% IUdR in controlling the viral keratitis.

Immune mechanisms against canine distemper. II. Role of antibody in antigen modulation and prevention of intercellular and extracellular spread of canine distemper virus

Specific antibody was shown to be highly effective in neutralizing extracellular canine distemper virus (CDV) as well as preventing the intercellular spread of this virus. Thus, relatively low levels of antibody neutralized 1 x 10(5) TCID50 of extracellular CDV and the development of plaques or CPE in Hep-2 and Vero cells respectively could be prevented even when up to 5% of the cells were infected. This inhibition of CPE and virus spread was most pronounced when antibody was added early but could still limit the degree of CPE if added as late as 48 h post-infection. This anti-viral activity was observed in different cell types including canine macrophages, cells normally infected with CDV in vivo. Prolonged exposure of infected target cells to high concentrations of antibody led to redistribution of surface viral antigens and their subsequent disappearance. The possible role of antibody in the defence against, and/or recovery from CDV and the mechanism(s) by which antibody may aid in recovery are discussed.

Mechanisms of heterotypic immunity against canine distemper

Hep-2 cells infected with measles virus (MV) for as short as 6 h became refractory to superinfection with canine distemper virus (CDV) but not to vesicular stomatitis virus (VSV). The exact mechanism of such interference is unknown but probably occurs after virus attachment and penetration. These results verify the suggestion that virus interference may be a mechanism of heterotypic protection against canine distemper.

Immunization of calves against enterotoxigenic colibacillosis by vaccinating dams with purified K99 antigen and whole cell bacterins

Pregnant cattle were either vaccinated subcutaneously with (i) a suspension of purified Escherichia coli K99 pili, (ii) a Formalin-killed whole cell bacterin containing enterotoxigenic E. coli strain B44 (O9:K30;K99:H-), or (iii) a bacterin containing six different strains of bovine enterotoxigenic E. coli (multiple-strain bacterin), or were left as nonvaccinated controls. After birth, calves were allowed to nurse their dams and, at 12 to 14 h of age, were challenged orally with 10(11) cells of enterotoxigenic E. coli strain B44. Colostral antibody titers were determined against K99, K30, and O9 antigens of B44. In the nonvaccinated control group, 9 of 10 calves developed diarrhea and died within 24 to 72 h. Similarly, all six calves in the multiple-strain bacterin group developed diarrhea and four died. In contrast to calves in the two groups mentioned above, calves nursing cows vaccinated with either purified K99 or the homologous whole cell bacterin were protected against fatal diarrhea. There was a highly significant correlation (P less than 0.0005) between protection against fatal diarrhea and K99, but not K30 or O9 colostral antibody titers. Vaccination of cows with either purified pili or whole cell preparations containing sufficient K99 antigen may provide a means of preventing enterotoxigenic colibacillosis in calves.

A new plaque system for canine distemper: characteristics of the green strain of canine distemper virus

A Vero cell adapted Green strain of canine distemper virus (CDV) was tested for its plaque-forming capacity in different cell lines. Plaque formation was observed in HEp-2, BS-C-1, and HeLa cells but not in Vero or dog kidney cells even though replication and cytopathology were observed in the latter cell types. In the cells in which the virus was capable of producing plaques, the plaques were observed within 24 h post infection and continued to increase in size with subsequent cellular destruction such that by 72 h postinfection the size of the plaques approached 0.5 mm. With the use of the plaquing technique, it was possible to demonstrate the thermal lability of the virus as well as the kinetics of adsorption. Thus, it was shown that the half-life of the virus was 125 min at 25 degrees C, 75 min at 35 degrees C, and 65 min at 37 degrees C. The rate of adsorption of CDV to HEp-2 cells was 17.2% in 30 min at 37 degrees C and continued slowly for 4 h before completion. Application of this rapid plaque-forming assay to plaque-reduction tests for CDV antibody and for CDV-infected cells by the infectious center assay are described.

Sudden death in young dogs with myocarditis caused by parvovirus

Sudden death of pups in the 4- to 6-week age range has recently been occurring in western Canada as a result of severe, primary, nonsuppurative myocarditis. At necropsy, the prominent macroscopic lesion was pulmonary edema, and microscopically, characteristic intranuclear inclusion bodies were found within cardiac myofibers in association with myocarditis. Ultrastructurally, numerous small particles resembling parvoviruses were found within the intranuclear inclusion bodies, which were positive by direct fluorescent antibody test for canine parvovirus. Of three pups inoculated with homogenate from affected myocardium, one developed lesions resembling canine parvoviral enteritis.

Immune mechanisms against canine distemper. I. Identification of K cell against canine distemper virus infected target cells in vitro

Canine peripheral blood lymphocytes, polymorphonuclear leucocytes (PMN) and monocytes (macrophages) were obtained by various cell separation techniques and were tested for their cytotoxic capacity against antibody-sensitized canine distemper virus (CDV) infected Vero cells by an in vitro chromium release assay. Canine lymphocytes were found to destroy CDV infected target cells effectively, while neither PMN nor monocytes (macrophages) could do so. The active lymphocyte was characterized by various rosetting techniques to be a non-T and a non-B lymphocyte. These cells bear no surface immunoglobulin (SIg-) but possessed both Fc receptors (Fc+) and complement receptors (EAC+) suggesting that these cells are neither classical T nor B cells. The possible roles of this K cell in the resistance against canine distemper are discussed.

Long-term culture of canine peripheral blood monocytes in vitro

Various cultural conditions were assessed for their ability to maintain canine peripheral blood monocytes in vitro. Approximately ten days after incubation of peripheral blood leukocytes in Earle's minimum essential medium supplemented with homologous red cell lysates and normal horse serum, virtually a pure macrophage culture was obtained which could then be maintained for about two months. This culture was judged to be pure by surface marker analysis and their phagocytic activity. The number of monocytes could be increased by injecting the dogs with a chloroform extract from Listeria monocytogenes prior to collection of the blood.

Equine respiratory disease on the Western Canadian racetracks

The serological results from this study clearly show that both equine influenza and equine rhinopneumonitis viruses were present during spring and autumn epidemics of respiratory disease on Western Canadian racetracks. Approximately 11% of the horses showed significant convalescent titres to influenza while 9% showed significant convalescent titres for equine viral pneumonitis. It was noted in our study a positive vaccination history corresponded with a reduction in the severity of the respiratory infection.

Induction, isolation and surface marker studies on bovine eosinophils

A crude extract from Ascaris suum was infused into the teat canal of heifers to serve as an irritant or an antigens. The cells present in the mammary gland following such stimulation were assessed over a period of 2 weeks. Prior to stimulation there were few cells, predominantly macrophages, however, by 12 h post-stimulation a larger number of eosinophils and neutrophils were present. The eosinophils, which represented approximately 50% of the total population, could be purified by Ficoll-Hypaque flotation and nylon or glass wool column filtration to yield a population consisting of over 90% eosinophils. Surface marker studies on the purified eosinophils revealed that they contained both Fc and complement receptors.

Isolation of various canine leucocytes and their characterization by surface marker analysis

Various techniques were used to separate canine peripheral blood leucocytes into populations enriched in lymphocytes, polymorphonuclear leucocytes, phagocytic mononuclear cells (monocytes) and macrophages. Surface markers on each cell population were determined by rosette formation. Fc receptors for IgG and complement receptors (C3b and C3d) were present on PMN, monocytes, macrophages as well as on a sub-population of lymphocytes. Purification of the lymphocytes into T-and B-cell-enriched populations revealed that these receptors were present only on the B lymphocytes and not on the T lymphocytes. In addition, a third lymphocyte population, which did not possess surface immunoglobulin, and Fc receptor but not the complement receptor. None of the cell populations exhibited C4 complement receptors or Fc receptors for IgM. When different cell populations were tested for their ability to form rosettes directly with human type 'O' red blood cells it was found that most populations could rosette, suggesting that this technique could not be used as a specific marker for canine T lymphocytes.

Mechanisms of recovery from Herpesvirus infections -a review

A variety of specific immunological mechanisms have been shown to be effective at neutralizing herpesviruses or destroying herpesvirus infected cells. These include both humoral and cell mediated immune responses or combinations thereof. Thus, it is genarlly accepted that humoral immunity is probably responsible for preventing reinfection whereas cellular immunity, mediated by T lymphocytes or by the interaction of antibody and Fc receptor bearing cells, is more important in recovery from infections. In addition to these specific responses to herpesvirus infection, a number of nonspecific cellular and humoral components have been shown to inhibit the progression of virus replication and therefore, have been implicated in assisting the host in the recovery process. The various interactions and counteractions between the various nonspecific and specific components of the immune response are discussed with respect to their role in recovery from both primary and recurrent disease as well as how they may eventually be manipulated so as to control herpesvirus recrudescent disease.

Direct lymphocytotoxicity against herpes simplex virus infected cells

This study was undertaken to determine if direct cytotoxicity (DC) against herpes simplex virus infected cells, perhaps mediated by T cells, could be demonstrated in individuals subject to recurrent herpes labialis. The mononuclear cells from 7 out of 17 individuals with recurrent herpes expressed DC whereas no DC was ever exhibited by 7 individuals without a previous history of herpes infections. Several approaches were used to show that the cytotoxicity being detected was predominately of the direct type rather than antibody-dependent cell cytotoxicity (ADCC). Since the effector cells of the DC were sensitive to trypsin treatment and behaved as do natural killer (NK) cells upon cell fractionation, the results were taken to imply that the DC was attributable to a NK-effector cell type rather than a classical T lymphocyte.

Identification of Trypanosoma theileri as a contaminant in primary cultures of bovine retina

T. theileri has been isolated from primary cultures of bovine retina and subcultered successfully for 2 passages in sub-confluent cultures. When cultures reached confluency no trypomastigotes or epimastigotes could be detected and attempts to recover trypanosomes from these cultures were unsuccessful. The presence of intracellular forms could not formally be excluded.

Comparison of rotavirus strains by hemagglutination inhibition

Rotaviruses have been shown to be of importance as aetiologic agents of gastroenteritis in infants and in domestic animals of several species. Hemagglutinins were prepared from two Canadian isolates of bovine rotavirus and from one isolate of a simian rotavirus. A United Kingdon isolate of bovine rotavirus was shown not to possess hemagglutinating activity, indicating a strain difference between a Canadian and United Kingdom bovine rotavirus. In hemagglutination-inhibition (HAI) tests a rabbit hyperimmune (two injections) serum, prepared to one of the bovine rotaviruses, was not helpful in distinguishing the two bovine viruses because of cross-reactions between the viruses. However, it was possible to distinguish the bovine viruses from the simian virus with this serum. When guinea pig immune sera were prepared to the four rotavirus strains and tested with the three hemagglutinins in the HAI test, antigenic differences between the four strains of rotavirus were demonstrated. Hyperimmune guinea pig serum prepared to a strain of human rotavirus did not inhibit any of three hemagglutinins indicating that the human strain is different from the three rotavirus strains which gave hemagglutinins.

Studies on the occurrence and significance of bovine respiratory syncytial virus in Saskatchewan

Seventy-six percent of 49 blood samples from Saskatchewan cattle had serum antibodies against bovine respiratory syncytial virus. Experimental infection of one week and seven month old calves with bovine respiratory syncytial virus (Iowa strain) caused transient fever, mucopurulent nasal discharge and coughing but no macroscopic or microscopic lesions attributable to bovine respiratory syncytial virus.

Neutrophils are mediators of antiviral immunity

The paper presents evidence that polymorphonuclear neutrophils upon stimulation with herpesvirus-induced antigens release a material inhibitory to virus infection. The material does not appear to be identical to type I or II interferon.

Human neutrophil--mediated destruction of antibody sensitized herpes simplex virus type I infected cells

Human peripheral blood polymorphonuclear neutrophils (PMN) were tested for their ability to act as effector cells in antibody-dependent cell cytotoxicity (ADCC) against Herpes simplex virus (HSV) infected target cells sensitized with anti-HSV serum. The PMN from all 29 individuals tested could mediate ADCC in the presence of a standard human anit-HSV serum. Since PMN are prominent cells early in herpes lesions, it was hypothesized that because ADCC could represent an in vitro model for antiviral recovery, perhaps the efficacy of PMN at mediating ADCC might be impaired in those subjects to frequent recrudescent herpes. However, evidence for the hypothesis was not obtained since the PMN from individuals with frequent, infrequent, or unrecorded herpes labialis all showed approximately the same activity at mediating ADCC. Alternative ways in which PMN could be involved in antiviral recovery were discussed.

Hemagglutination and hemagglutination-inhibition studies with a strain of Nebraska calf diarrhea virus (bovine rotavirus)

A hemagglutinin has been prepared from Nebraska calf diarrhea virus (NCDV) propagated in BS-C-1 cell line. After cesium chloride centrifugation, the hemagglutinin of the bovine rotavirus was found to be associated with intact virions (density 1.355 g/ml) but not with virions lacking an outer capsid layer (density 1.375 g/ml). In hemagglutination-inhibition (HAI) tests, the hemagglutinin reacted specifically with NCDV serum, and HAI seroconversions were detected in some sera tested. Cross-reactions were observed in complement fixation tests between the human and bovine rotaviruses but were not demonstrated by HAI, suggesting that the hemagglutinin detects a specific rather than a group antibody response.

Immune effector cell activity in canines: failure to demonstrate genetic restriction in direct antiviral cytotoxicity

Experiments were undertaken to establish whether the cytotoxic activity of canine immune effector cells against viral antigens was affected by the genotype of the target cell (genetic restriction). Puppies from three different breeds were infected with vaccinia virus, and the peripheral blood leukocytes were collected at various times for measurement of their cytotoxicity against autologous and heterologous vaccinia virus-infected and uninfected skin fibroblasts. In all cases cytotoxicity only occurred against virus-infected targets, and there was no consistent evidence of preferential killing of autologous targets. Several indirect approaches were used to demonstrate that direct, presumably T cell, cytotoxicity was being measured rather than antibody-dependent cell cytotoxicity. On the basis of the evidence from cross mixed-lymphocyte assays and cell-mediated lympholysis assays, the dogs were shown not be be identical with respect to their histocompatibility antigens. The significance of our findings to the phenomenon of genetic restriction as observed for mouse-derived immune effector cells is briefly discussed.

Characterization of surface receptors on bovine leukocytes

Three bovine leukocyte populations--peripheral blood lymphocytes (PBL), mammary gland polymorphonuclear neutrophils (PMN) and macrophages (Mo)--were characterized with respect to five surface markers: surface immunoglobulin (SIg), sheep erythrocyte receptor, complement (C) receptor and Fc receptors for both IgG and IgM. The majority of PMN and Mo possessed C and Fc receptors for IgG, but lacked SIg and the erythrocyte receptor. The PMN, but not Mo, also expressed a Fc receptor for IgM. The PBL were heterogeneous with respect to their surface characteristics and evidence was presented for the following subtypes: (a) cells with the E receptor alone; (b) cells with E receptor plus the Fc(IgG) receptor; (c) cells with SIg plus the C receptor but minus the Fc(IgG) receptor; (d) lymphocytes with SIg plus the C receptor and the Fc(IgG) receptor, and (e) cells lacking E receptors and SIg but bearing Fc(IgG). It was assumed, but not proven, that some of these latter cells must also bear the C receptor. The significance of the various cell types in antiviral defense is briefly discussed.

Interactions between effector cell activity and lymphokines: implications for recovery from herpesvirus infections

The destruction of herpesvirus-infected target cells by antibody-dependent and direct cell cytotoxicity was enhanced by the presence of bovine lymphokine-containing preparations. To relate these effects to possible in vivo mechanisms of recovery, several in vitro approaches were used to measure the effects of lymphokine-containing preparations on controlling viral spread. In the first approach it was shown that in the presence of lymphokines, virus-infected cells could be killed earlier in the replication cycle by the mechanism of antibody-dependent cell cytotoxicity, thus possibly limiting spread of virus. That this was indeed the case was demonstrated by a decrease in the area of viral-induced cytopathology as well as in the total number of infected cells present. Secondly, the amount of infectious virus released was also markedly reduced in cultures incubated with lymphokines and immune peripheral blood lymphocytes as compared to cultures treated with either component alone. Finally, lymphokines caused the activation of macrophages. These results are discussed in terms of how various immune parameters may interact in a positive way so as to aid in the recovery from virus infection.

Rotavirus isolation and cultivation in the presence of trypsin

Rotaviruses are generally difficult to isolate and culture in vitro; therefore, virus isolation has not been used as a method of diagnosing this group of agents. The present report describes a simple procedure for isolating bovine rotaviruses directly from feces after pretreatment of fecal samples with trypsin. This procedure resulted in virus isolation from five of five samples that contained virus particles, as demonstrated by electron microscopy, and four of seven samples where virus particles could not be observed but were considered positive by the presence of immunofluorescent-staining cells in feces. Virus could not be isolated from "normal" feces. If the virus was not passaged in the presence of trypsin, the infectivity was gradually lost, but infectivity could be restored again if trypsin was added, resulting in increased virus spread and concomitant increase in virus yield. The application of this technique as a diagnostic tool for bovine and other rotaviruses is briefly discussed.

Enhancement of antibody-dependent cell-mediated cytotoxicity of herpesvirus-infected cells by complement

An investigation was made of the effects of complement on the levels of antibody-dependence cytotoxicity (ADCC) mediated by bovine leukocytes against herpesvirus-infected target cells. Neutrophil-mediated ADCC was considerably enhanced upon the addition of low levels of complement that alone failed to induce lysis of antibody-sensitized target cells. This enhancement was most apparent under suboptimum conditions such as at low effector-to-target cell ratios, low levels of sensitizing antiserum, and short-duration assays. Furthermore, cells and classes of immunoglobulin unable to induce ADCC could do so in the presence of complement. The action of complement is considered in terms of a more tenacious bond formed between effector and target cells. The implications of the results are discussed in terms of the part that complement might play in enhancing antiviral recovery processes.

The effect of the antiherpesvirus drug 5-methoxymethyl-2'-deoxyuridine on the humoral immune response in vivo

5-Methoxymethyl-2'-deoxyuridine (MMUdR), a drug with potent antiviral activity in vitro against Herpes simplex virus, was investigated for its immunosuppressive effects. Doses as high as 2000mg/kg given daily for 9 days were not immunosupporessive as judged by the fact that treated animals produced normal immune responses to sheep erythrocytes, Brucella bacteria, and Herpes simplex virus.

Solid-phase radioimmunoassay for detecting bovine (neonatal calf diarrhea) rotavirus antibody

An indirect solid-phase microradioimmunoassay is described for detecting antibodies against rotaviruses. The test involved ethanol fixation of microcultures of bovine rotavirus-infected BSC-1 cells and reacetion with bovine antirotavirus serum, followed by 125I-labeled rabbit anti-bovine immunoglobulin G. The technique was shown to be virus specific and highly sensitive. The fixed microcultures could be stored at 4 degrees C for at least 2 months without affecting the sensitivity of the test. The application of this system for the detection of rotavirus antibodies in humans is briefly discussed.

The role of neutrophils in antiviral defense--in vitro studies on the mechanism of antiviral inhibition

Highly enriched populations of bovine neutrophils were added, in the presence of antiviral antibody, to herpesvirus-infected bovine cell cultures. A cell dose-dependent reduction in virus-induced cytopathology was observed. The mechanism of inhibition was presumed to be mediated by a subcellular neutrophil product and not the result of either direct cytotoxicity or antibody-dependent cell-mediated cytotoxicity (ADCC). Thus, inhibition of comparable magnitude was observed when neutrophils and virus-infected cells were separated by cell impermeable membranes. In addition, plaque reduction occurred when antiviral immunoglobulins or fragments unable to mediate ADCC were used in the assays. Killed neutrophils and sonicates were unable to mediate plaque inhibition. Speculations were made as to the origin of the virus-inhibitory substances and the role that neutrophils might assume in mediating recovery from virus infection.

Mechanisms of resistant of herpesviruses: comparison of the effectiveness of different cell types in mediating antibody-dependent cell-mediated cytotoxicity

Enriched populations of polymorphonuclear leukocytes (PMN) and macrophages obtained from the mammary gland and of granulocytes (PBG) and lymphocytes (PBL) prepared from peripheral blood of the same animal were compared for their ability to mediate antibody-dependent cell cytotoxocity against antibody-sensitized infectious bovine rhinotracheitis virus-infected target cells (IBR-GBK) and antibody-sensitized chicken erythrocyte targest (CRBC). The order of effectiveness was PMN leads to macrophages leads to PBG leads to PBL. The reason why PBG (86% PMN) were less than 50% as active as mammary PMN (99% PMN) was explored and discussed. The findings that PMN were more effective on a cell-to-cell basis, required less antiserum to sensitize for cytotoxicity, and destroyed IBR-GBK cells faster and more completely than other cell types could mean that PMN may be the cell type most importnat in causing early recovery from herpesvirus infections.

The direct antiviral cytotoxicity by bovine lymphocytes is not restricted by genetic incompatibility of lymphocytes and target cells

Experiments were designed to determine if in the ox a requirement for genetic compatibility between antiviral cytotoxic cells and target cells was needed for cytotoxicity to occur. Unrelated bovine animals were immunized with vaccinia or IBR virus (a herpesvirus), and PBL were collected at various times for measurement of their cytotoxicity against autologous or heterologous uninfected or virus-infected fibroblasts. In all instances, cytotoxicity was expressed against heterologous as well as autologous targets and in most cases there was no evidence of enhanced killing of autologous cells. The cytotoxicity was shown to be direct, presumably T cell mediated, and was not attributable to ADCC. The likelihood of the animals under investigation sharing histocompatibility antigens was considered extremely remote but was not formally excluded.

Bovine type II interferon: activity in heterologous cells

The antiviral and cell growth inhibition spectra of bovine and human interferons are described. The antiviral activity of type II interferon in heterologous cells far exceeded that of the corresponding type I interferon. Antiviral activity of bovine type II interferon parallels cell growth inhibition activity both in thermal inactivation kinetics as well as in the rate of synthesis. Furthermore, the spectrum of antiviral activity against heterologous cells was the same as that seen for cell growth inhibition suggesting that one molecule may mediate both effects. The therapeutic implications of type II interferon prepared in animals for use in human medicine are discussed briefly.

Polymorph-mediated antibody-dependent cytoxicity--modulation of activity by drugs and immune interferon

Bovine polymorphonuclear leukocytes (PMN) mediated antibody-dependent cell cytotoxicity (ADCC) against erythrocyte and herpes virus-infected target cells. The extent of cytotoxicity was not affected by drugs that inhibited DNA, RNA, or protein synthesis. The effect did not occur in the absence of divalent cations, was suppressed by pretreatment of PMN with silica and cytochalasin B, and was subject to the bidirectional control by cyclic nucleotides; drugs decreasing cyclic AMP or elevating cyclic GMP levels enhanced ADCC. The ADCC phenomena was also enhanced by supernates containing immune interferon activity from antigen-stimulated-immune lymphocyte-macrophage cultures. The possibility that immune interferon(s) might be causing the elevation of ADCC and the relevance of this observation in terms of the part interferon might play in modulating recovery from herpes virus infections was discussed.

Erythrocyte rosettes--a marker for bovine T cells

Many species of erythrocytes were investigated for their ability to form spontaneous rosette with bovine peripheral blood leukocytes and fetal thymocytes. Only sheep and chicken red blood cells gave rosettes. Using conditions shown optimum for the demonstration of human rosette forming cells, only low numbers of bovine rosettes were demonstrable. By changing culture conditions to include 100% fetal calf serum, neuraminidase treated erythrocytes and/or lymphocytes and optimizing the incubation times and temperature, up to 38% of peripheral blood leukocytes and 52% of thymocytes formed rosettes. A thymic origin of rosetting cells was ascribed to T cells for the following reasons: 1) thymocytes gave higher numbers than did peripheral blood leukocytes, 2) rosette forming cell numbers were increased in peripheral blood leukocyte subpopulations enriched in T cells by nylon column separation and 3) only very few rosette forming cells had surface immunoglobulin, a marker of B lymphocytes. The reasons why all T cells were not detected by the technique were discussed.

Observations on recovery mechanisms from feline viral rhinotracheitis

Experiments were designed to determine immunological mechanisms responsible for controlling dissemination of feline rhinotracheitis virus in feline cell cultures. Virus infected cells could be destroyed by three mechanisms--antibody and complement mediated lysis, direct lymphocyte cytotoxicity and antibody dependent cell-mediated cytotoxicity. This latter immune parameter was mediated by both lymphocytes and macrophages and varied in extent in different cats. To ascertain the potential importance of the immunological parameters in curtailing viral spread, the time when virus infected cells could be destroyed by each component was related to the chronological events of viral replication and dissemination. Intracellular infectious virus and intracellular spread occurred at six to seven hours postinfection and extracellular spread at nine to ten hours postinfection. Antibody complement lysis and antibody dependent cell-mediated cytotoxicity occurred at six hours postinfection and direct cytotoxicity at eight hours postinfection. The relevance that these findings might have in relation to the occurrence and frequency of recrudescent disease is discussed.

Immune interferon production by lymphoid cells: role in the inhibition of herpesviruses

Bovine peripheral blood lymphocytes (PBL) obtained from infectious bovine rhinotracheitis (IBR) virus- and tuberculin-immunized animals produced large quantities of interferon within 24 h of in vitro stimulation by IBR and purified protein derivative antigens. Separation of PBL into populations enriched in T lymphocytes or B lymphocyte provided the antigen-specific step for immune interferon production. A 2- to 10-fold increase in interferon occurred when lymphocytes were combined with autologous macrophages. Although macrophages, even if treated with antilymphocyte serum to remove any contaminating lymphocytes, could produce some interferon, the augmented interferon produced by macrophage-lypmhocyte cultures was not dmpocytes. Direct physical contact between macrophages and lymphocytes was required for the production of enhanced levels of interferon. Antigen-antibody complexes of irradiated virus-infected cells in the presence of antibody were as efficient or better at stimulating interferon than was free antigen. Because IBR virus was inhibited by interferon levels stimulated in cultures by IBR antigen, it was suggested that the local production of interferon by immune cells might play a similar role in curtailing virus dissemination in vivo, thus leading to recovery from disease.

Ribonucleotides in infectious bovine rhinotracheitis virus DNA

Infectious bovine rhinotracheitis (IBR) virus was grown in the presence of 5-3H-uridine in a continuous line of bovine kidney cells. 5-3H-uridine was found to be associated with viral nucleocapsids. Furthermore, purification of the viral nucleic acid present in nucleocapsids illustrated that 5-3H-uridine was part of the viral nucleic acid. Purification of viral DNA from infected cells also indicated that 5-3H-uridine was associated with viral nucleic acid possibly as ribonucleotides. The label was identified as RNA by measuring its susceptibility to RNase and analysis of the bases. Short pulses with 5-3H-uridine, resulted in labelled nucleic acid which was extremely sensitive to RNase and alkali but resistant to DNase. Nucleotide analysis indicated that after short pulses all the radioactivity was associated with the base uracil whereas upon longer labelling periods a large percentage of the label was associated with cytosine. However even if viral DNA was isolated from nucleocapsids there was still some radioactivity associated with uracil. Sedimentation of heat denatured 5-3H-uridine label viral nucleic acid in CS2SO4 indicated that the label sedimented at a density of single stranded DNA suggesting that the ribonucleotides are covalently linked to the viral DNA.

Antibody-dependent cell-mediated cytotoxicity in cows: comparison of effector cell activity against heterologous erthrocyte and herpesvirus-infected bovine target cells

Bovine peripheral blood leukocytes (PBL) and cells collected from the bovine mammary gland were assayed for antibody-dependent cell-mediated cytotoxicity (ADCC) against chicken erythrocyte (CRBC) and bovine herpesvirus-infected bovine kidney cell targets. Bovine antisera were used to sensitize target cells. Both PBL and mammary leukocytes expressed ADCC, with the latter cell population having greater activity against both target cells. Only the CRBC target cells were killed by nonadherent PBL and phagocyte-depleted PBL. Nonadherent mammary leukocytes, rich in monocytes and macrophages, did kill virus-infected target cells. Carbonyl iron-treated mammary leukocytes failed to kill virus-infected targets but could destroy CRBC targets. Antimacrophage serum inhibited lysis of both CRBC and virus-infected targets, but antilymphocyte serum only inhibited CRBC killing. These observations indicated that at least two kinds of cells could mediate ADCC against CRBC but only cells of the mononuclear phagocytic series could kill virus-infected target cells. The herpesvirus-infected target cells became susceptible to ADCC 9 h after virus infection. A case is made for investigating the phenomenon of ADCC using in vitro systems that closely mimic the in vivo situation. The possible role of the ADCC mechanism as instrumental in causing recovery from herpesvirus infections is discussed.

Lymphocyte activation by cell separation procedures

Cell separation techniques normally used to obtain subpopulations of lymphocytes were shown, under certain conditions, to render the cells cytotoxic towards a number of target-cells including autologous lymphocytes. To cause cytotoxicity, it was necessary to pass cells through glass wool and/or nylon wool columns equilibrated with media containing fresh plasma or serum. Cells lost activation upon overnight in vitro culture or treatment with trypsin. In addition to direct cell cytotoxicity, cells released heat labile cytotoxic factors and antibody during the separation procedures. The implications of the results for the interpretation of cell separation studies designed to attribute immunological effects to one or another cell type were discussed.

Comparison of the antiviral effects of 5-methoxymethyl-deoxyuridine with 5-iododeoxyuridine, cytosine arabinoside, and adenine arabinoside

The antiviral activity of 5-methoxymethyl-2'-deoxyuridine (MMUdR) was compared with that of 5-iodo-2'-deoxyuridine (IUdR), cytosine arabinoside (Ara-C), and adenine arabinoside (Ara-A). At concentrations of 2 to 4 mug/ml, MMUdR was inhibitory to herpes simplex virus type 1, but concentrations as high as 128 mug/ml were not inhibitory to three other herpesviruses tested (equine rhinopneumonitis virus, murine cytomegalovirus, and feline rhinopneumonitis virus) or to vaccinia virus. The other nucleosides, in contrast, were inhibitory at similar concentrations (1 to 8 mug/ml) against all viruses tested. The inhibition of HSV-1 by MMUdR appeared to be the result of interference with virus replication rather than the result of drug toxicity to host cells. The drug was not toxic to host cells at 100 times the antiviral concentrations, and pretreatment of host cells with high concentrations of MMUdR had no effect on subsequent virus replication. Combination of MMUdR with either IUdR, Ara-A, or Ara-C gave an enhanced antiviral effect, suggesting that the mechanism of action of MMUdR is different from that of the other three drugs. Antiviral indexes were calculated for each compound and were found to be >250, 80, 40, and 8 for MMUdR, IUdR, Ara-A, and Ara-C, respectively. These were defined as the minimum dose at which toxicity was observed microscopically divided by the dose which reduced plaque numbers by 50%.

Effect of anti-herpesvirus drugs on human and bovine lymphoid function in vitro

Lymphocyte proliferative responses to phytohemagglutinin, pokeweed mitogen, and herpesvirus (herpes simplex virus and infectious bovine rhinotracheitis virus) antigens were evaluated in the presence of various concentrations of the anti-herpesvirus drugs, methylmethoxydeoxyuridine (OCH3CH2UdR), cytosine arabinoside was inhibitory at 25 mug/ml and cytosine arabinoside was inhibitory OCH3CH2UdR per ml, lymphocyte proliferative responses were unaffected and were not abolished even by concentrations of 2,500 mug/ml. In contrast, adenine arabinocide was inhibitory at 25 mug/ml and cytosine was inhibitory at 5 mug/ml. Both direct and antibody-dependent lymphocyte cytotoxicity of herpesvirus-infected target cells were highly resistant to OCH3CH2UdR; concentrations of 1,000 mug/ml were only marginally inhibitory. The anti-herpesvirus activity of all three drugs is similar (0.5 to 8 mug/ml) (L.A. Babiuk, B. Meldrum, V.S. Gupta, and B. T. Rouse, submitted for publication). The drug OCH3CH2UdR should be given a careful, well-controlled evaluation of its effectiveness in the treatment of herpes simplex infections in animals, perhaps including humans, since our results using in vitro models show that cellular responses important for recovery from herpesvirus infections are unaffected by doses far in excess of those found be be antiviral.

Defense mechanisms against bovine herpesvirus: relationship of virus-host cell events to susceptibility to antibody-complement cell lysis

The interaction of infectious bovine rhinotracheitis virus and susceptible host cells was examined to determine whether an infected cell could be destroyed by humoral immune mechanisms before or after the transmission of virus to susceptible adjacent cells. Viral antigens were detectable on cell membranes at 6 h postinfection, but cells were not susceptible to antibody-complement lysis until 10 h postinfection. Intracellular infectious virus was also detectable at 10 h postinfection, and transmission to adjacent cells by the intracellular route began at this time. Extracellular virus was not detectable until 12 to 13 h postinfection. By the continual addition of antibody and complement, virus dissemination could be reduced more than 50-fold. These results support the hypothesis that the humoral immune mechanism may be involved in the recovery from herpesvirus infections.

Defense mechanisms against infectious bovine rhinotracheitis virus: inhibition of virus infection by murine macrophages

An in vitro method is described to measure the inhibitory activity of murine peritoneal exudate cells against viral plaque formation by a bovine herpes-virus-infectious bovin'e rhinotracheitis virus. Microtiter plates containing 96 bovine kidney cell monolayers were infected with a range of virus concentration and peritoneal exudate cells were subsequently added. When a sufficient number of cells was added, viral plaques were not detectable and free infectious virus did not occur in the culture fluids. The inhibitory cell type adhered to glass and was presumably a macrohage. Although inhibitory of viral plaques was presumably a macrophage. Although inhibition of viral plaques was complete and free virus could not be detected, virus was not eliminated from the monolayers since on removal of cells, the degree of virus cytopathology and yield of virus after a further 48 h of incubation was the same as in 48-h infected control monolayers. The significance of peritoneal exudate-cells-induced virus suppression as a model to understand herpesvirus latency is briefly discussed.?Author