Variables affecting viral plaque formation in microculture plaque assays using homologous antibody in a liquid overlay

A liquid antibody microculture plaque assay and the variables that govern its effectiveness are described. The assay is based on the principle that low concentrations of homologous antibody can inhibit secondary plaque formation without inhibiting formation of primary plaques. Thus, clear plaques that followed a linear dose response were produced. The assay was found to be more rapid, less cumbersome, and less expensive than assays using agar overlays and larger tissue culture plates. It was reproducible, quantitative, and had about the same sensitivity as the agar overlay technique in measuring infectious coxsackievirus type B-3. It was more sensitive in assaying adenovirus type 3 and Western equine encephalomyelitis, vesicular stomatitis, Semliki forest, Sendai, Sindbis, and Newcastle disease viruses than were liquid, carboxymethylcellulose, and methylcellulose microculture plaque assays. The variables influencing sensitivity and accuracy, as determined by using coxsackievirus type B-3, were: (i) the inoculum volume of virus; (ii) the incubation period of virus; and (iii) the incubation temperature.

Benign ulceration of the cecum

Three proved cases of benign ulceration of the cecum are presented, 2 with acute onset of abdominal pain, the third with acute hemorrhage. The clinical, pathological, and variable radiographic features are described.

Interferon induction by radioprotective mercaptoalkylamines and derived thiophosphates

Radioprotective thiols (five mercaptoalkylamines and four derived thiophosphates) induced interferon and resistance to virus infection. Interferon production occurred in human and mouse nonlymphoid cell cultures. One of the thiols, S,2-aminoethylisothiourea, given intraperitoneally, protected mice against two unrelated viruses--Semliki forest virus and Herpesvirus hominis type 1. Two structurally different radioprotective thiols--the disulfide cystamine and L-cysteine--were unable to induce the firus resistance state or interferon.

Interferon induction in cynomolgus and rhesus monkey after repeated doses of a modified polyriboinosinic-polyribocytidylic acid complex

Serum interferon activity was determined in 12 cynomolgus and 12 rhesus monkeys injected intravenously once daily for 10 days with from 0.1 to 6.0 mg of a stabilized polyriboinosinic acid . polyribocytidylic acid complex per kg, composed of polyriboinosinic acid . polyribocytidylic acid, poly-1-lysine, and carboxymethylcellulose [poly(ICLC)]. Interferon activity was detected 2 h after the first injection, with maximum activity occurring 8 h after the second injection. A period of hyporesponsiveness occurred after the third injection of poly(ICLC) in all monkeys and lasted until the sixth injection in the rhesus monkeys, when interferon activity again became more elevated. The delayed rebound was not as apparent in cynomolgus monkeys. Rhesus monkeys injected with 6 mg/kg did not exhibit serious side effects.

Vesicular stomatitis virus plaque production in monolayer cultures with liquid overlay medium: description and adaptation to a one-day, human interferon-plaque

Vesicular stomatitis virus forms discrete, microscopic plaques in stationary cultures of the WISH amnion cell line. Microplaque formation is rapid, reproducible, and easily quantitated, occurs at temperatures ranging from 33 to 40 degrees C, and does not require a semisolid overlay. WISH cells, however, are less sensitive to vesicular stomatitis virus than are chicken embryo, 3T6, or Vero cells. WISH amnion cells also are highly sensitive to the antiviral effects of human interferon, and a quantitative human interferon assay, based on vesicular stomatitis virus plaque reduction in WISH cells, is described. This interferon assay can be performed within 1 day, uses a liquid overlay medium, does not require a vital stain, is as sensitive as other methods that use diploid cell strains, and is performed in a microtiter system.

Interferon: effects on the immune response and the mechanism of activation of the cellular response

The discovery of interferon in 1957 by Drs. Isaacs and Lindenmann led to major revisions in the concepts of man's defenses against viral infections. There are at least two types of interferon. Along with their antiviral properties, they have recently been shown to exert a suppressive effect on the humoral and cellular immune response; they affect both B and T lymphocytes. A variety of substances, including virus, polyribonucleotides, and mitogens for T lymphocytes, are good interferon inducers. T lymphocytes seem to be necessary for these inducers to exert their immunosuppressive effects. The immunosuppressive effects of interferon inducers suggests that interferons may be mediators of suppressor T lymphocyte effects. In the virus system, interferon does not exert its antiviral effects by direct action on the virus, but rather derepresses a cell gene that results in the production of an antiviral protein. This antiviral protein is probably the mediator of inhibition of virus replication. This is a complex sequence of events that results in the interaction of interferon with the cell membrane and the resulting production of the antiviral state in the cell. This review will examine the various steps of this involved process.

Kinetics of the rapid action of interferon

The present study was undertaken to examine some factors which lead to early-appearing resistance in human cells treated with interferon. It was previously shown that two conditions required for rapid development of resistance were continuous maintenance of cultures at 37 degrees and use of more than 10 units/ml of interferon. The decay kinetics of the established resistance appear to be approximately the same whether the resistance was induced under conditions favoring rapid or slow development. With the use of actinomycin D it was shown that the mRNA for the antiviral protein is produced between 30 and 45 min after the first contact with interferon. Ruled out were the possibilities that a priming action of interferon and a newly synthesized intermediary protein were necessary for rapid development of resistance.

A phase I-II trial of multiple-dose polyriboinosic-polyribocytidylic acid in patieonts with leukemia or solid tumors

Polyriboinosinic-polyribocytidylic acid (poly I - poly C), an interferon inducer, was administered in multiple doses of 0.3-75 mg/m2 to 26 patients with a variety of solid tumors, 9 with acute leukemia, and 2 with chronic myelogenous leukemia in blast crisis. Forty-four separate drug trials were comprised of various schedules and routes of administration. Toxic reactions included fever (in 66% of the trials), transient elevation of serum glutamic-oxaloacetic transaminase and serum glutamic-pyruvic transaminase (25%), minimal laboratory evidence of coagulation abnormalities (59%), and hypersensitivity (5%). These toxic manifestations did not relate to dose level or magnitude of interferon induction. Poly I - poly C administered iv induced low serum concentrations of interferon in 24/38 trials (63%), but the correlation between drug dose and peak interferon titer was not linear. Poly I - poly C administered iv or im was not effective as an inducer of interferon in the cerebrospinal fluid. Similarly, poly I - poly C administered im or by inhalation did not produce detectable serum levels of interferon. No patients experienced an objective tumor response to the administration of poly I - poly C, and most (76%) had progression of their disease while receiving the drug.

Prophylactic control of simian hemorrhagic fever in monkeys by an interferon inducer, polyriboinosinic-polyribocytidylic acid-poly-L-lysine

A nuclease-resistant complex of polyriboinosinic-polyribocytidylic acid containing poly-L-lysine and carboxymethylcellulose was used as prophylactic treatment of simian hemorrhagic fever in rhesus monkeys. This infection has proven uniformly fatal to more than 50 monkeys. Treatment 8 hr before infection and repeatedly thereafter completely prevented the development of viremia and death. Untreated animals died before development of antibodies to the virus. None of the treated animals developed antibody to the virus, a fact which suggested that viral growth was essentially completely blocked by the compound.

Three strains of influenza A virus (H3N2): interferon sensitivity in vitro and interferon production in volunteers

Three antigenic variants of the H3N2 subtype of wild-type influenza A virus (representing the years 1968, 1972, and 1974) were examined for their sensitivity to interferon and for their ability to induce local respiratory tract interferon in volunteers. In addition, the time of appearance of symptoms in infected volunteers was correlated with the patterns of virus shedding and interferon production. The sensitivity to interferon and the ability to stimulate nasopharyngeal interferon were similarly high for all three strains. Symptomatic illness, peak virus shedding, and peak interferon response all occurred within a 26-h period. These findings imply that interferon or its inducers theoretically could be protective if applied prophylactically, but would be less efficacious when used therapeutically.

Comparative production of interferon by explanted lymphoreticular tissue and alveolar macrophages from rabbits and humans

Studies were undertaken to compare interferon production among a variety of lymphoreticular cells, with emphasis on the alveolar macrophage. Explanted cells from rabbit lung, spleen, peritoneum, bone marrow, and blood produced interferon in varying amounts in response to six of the seven viruses studied. The various lymphoreticular tissues responded differently to a single interferon-inducing virus, and each tissue produced varying amounts of interferon when stimulated by different viruses. In addition, glass-adherent rabbit alveolar macrophages produced more interferon than did the nonadherent subpopulation. Human blood and lung cells produced much less interferon than did the equivalent rabbit cells under similar conditions of stimulation. It appeared that interferon production may have been controlled by several variables, including the species, the type of inducer, and the type of tissue and cell.

5-iododeoxyuridine potentiation of the replication in vitro of several unrelated RNA and DNA viruses

Enhancement of the replication of unrelated viruses (three RNA viruses and one DNA virus), representative of four major virus groups, occurs in human, rodent, or avian cells treated in vitro with 5-iododeoxyuridine (IdU). The results suggest that the potentiation of viral replication by IdU is a widespread phenomenon.

Absence of detectable interferon in jejunal biopsies, jejunal aspirates, and sera in experimentally induced viral gastroenteritis in man

Seven of thirteen normal volunteers inoculated with either the Norwalk of Hawaii agent of viral gastroenteritis demonstrated clinical illness, with typical rapid onset, short duration, and rapid recovery. Examination of sera, jejunal aspirates, and jejunal biopsy specimens obtained 48-96 hr after inoculation, failed to reveal the presence of interferon in samples from either ill or well subjects.

Murine cytomegalovirus: induction of and sensitivity to interferon in vitro

Moderate amounts of viral inhibitor were produced by mouse embryo (ME) cultures infected with two strains of plaque-purified murine cytomegalovirus (MCV). This inhibitor was shown to be interferon, based on the possession of similar properties. The growth studies of MCV in ME cells showed that interferon was produced as early as 4 h after infection, infectious virus was produced between 12 to 16 h, and cytopathic effect was produced between 16 to 18 h. Since MCV-induced interferon production and the subsequent development of antiviral state occurred early, the long eclipse period may be due to an interferon-mediated delay of virus replication. Pretreatment of ME cells with varying concentrations of interferon before infection with MCV did not result in increased interferon production, but at high pretreatment doses a slight inhibitory effect on interferon production was observed. In vitro sensitivity studies showed that small doses of MCV were highly sensitive to the antiviral action of interferon, but higher viral doses proved to be markedly resistant. Although the available evidence does not permit a definitive interpretation of the mechanism by which MCV may show differing sensitivities to interferon action, the presence of a small interferon-resistant fraction of virus-infected cells may account for the observations.

A modified polyriboinosinic-polyribocytidylic acid complex that induces interferon in primates

A comlex of polyriboinosinic-polyribocytidylic acid (poly I-poly C) with poly-L-lysine and carboxymethylcellulose has been prepared. This complex is five to 10 times as resistant to hydrolysis by primate serum as the parent poly I-poly C. It has a thermal denaturation temperature about 40 C higher than that of poly I-poly C. The complex induces significant levels of serum interferon in monkeys and chimpanzees under conditions in which poly I-poly C itself induces no interferon.

Inhibitory effect of synthetic polyribonucleotides on the primary in vitro immune response

The synthetic double-stranded polyribonucleotides, poly (rA):poly (rU) and poly (rI):poly (rC), were shown to be potent inhibitors of the in vitro plaque-forming cell (PFC) response to a thymus-dependent (SRBC) and thymus-independent (E. coli 0127 LPS) antigen in mouse C57BL/6 spleen cell cultures. The same polynucleotides had no effect on the PFC response of nude (athymic) mouse spleen cells to E. coli 0127 LPS, suggesting that functional T lymphocytes are necessary for the inhibitory effect. Enhancement effects were modest and inconsistent in the cultures. Poly (rA) and poly (rU) were ineffective as inhibitors. The data indirectly suggest that the inhibition may be due to the early production of interferon by functional T lymphocytes.

Failure of attenuated temperature-sensitive influenza A (H3N2) virus to induce heterologous interference in humans to parainfluenza type 1 virus

The present investigation was undertaken to determine if a candidate live vaccine virus, influenza A/Hong Kong/68-ts-1 [E] (H3N2), induced heterologous interference against an interferon-sensitive, wild-type, parainfluenza type 1 challenge virus. The parainfluenza virus was administered 7 days after Hong Kong/68-ts-1 [E] virus infection. The clinical response, daily quantitative virus shedding, interferon production, and serum and nasal wash antibody responses were determined in an experimental group (influenza A virus followed by parainfluenza virus) and 10 volunteers in a control group (parainfluenza virus only). The volunteers were selected on the basis of susceptibility to the two viruses, i.e. serum hemagglutination-inhibition antibody titer of is less than or greater to 1:8 for influenza virus and low nasal wash antibody titer (is less than or greater to 1:8) for parainfluenza virus. Despite a 100% infection rate in the Hong Kong/68-ts-1 [E] vaccinees, no heterologous interference was induced against the parainfluenza type 1 virus challenge.

Studies of herpes simplex virus and interferon in human gingival cell cultures

Cultures of human gingival fibroblast cells from patients with a positive or negative history of recurrent herpes simplex virus (HSV) infection were compared with respect to susceptibility to HSV infection and interferon activity. There was a possible inverse relationship between interferon sensitivity of gingival fibroblast cells and a clinical history of recurrent disease. No correlation was found between prior infection and other parameters of interferon activity or susceptibility of the cells to HSV.

Inhibition of the primary in vitro antibody response by interferon preparations

The primary in vitro plaque forming cell (PFC) response of mouse (C57BL/6J) spleen cells to sheep red blood cells (SRBC) was inhibited by two sources of crude and two sources of partially purified mouse interferon. The substance(s) in the interferon preparations which induced PFC and antiviral inhibitory activity have the following common characteristics: a) The interferon preparations were of different potencies and specific activities, but they inhibited the PFC response in proportion to their activities; 20 to 60 units were the minimal amounts required for greater than 90% inhibition of the PFC response. b) Both the antiviral activity and the PFC inhibitory activity of the interferons were neutralized by antibody specific for mouse interferon. c) Both activities were partially or completely inactivated by heating at 60 degrees C for 1 h. d) Human interferons had neither antiviral activity nor PFC inhibitory activity in mouse cells. e) Limited exposure (4 h) of cells to interferon significantly inhibits both viral infection and the PFC response. f) Both the antiviral activity and the PFC inhibitory activity of the interferon preparations are acid stable. It is concluded, therefore, that the inhibition of the primary in vitro PFC response is due to interferon in the preparations. Maximum inhibition of the PFC response occurred when interferon was added to cultured at the same time as SRBC. Significant inhibition was also observed when interferon was added 1 day later, and slight enhancement was observed when added at days 2 and 3 of SRBC addition. Kinetic data showed that the greater the concentration of interferon added to the cultures, the earlier the effect on the PFC response. The presence of interferon in cultures for the first 4 h is sufficient to inhibit the PFC response. Interferon, then, appears to affect some early event(s), which leads to inhibition of the PFC response. Since mature T cells can be one of the sources of interferon, we have demonstrated a suppressor effect of a T cell lymphokine. The precise relationship of interferon to various expressions of suppressor T cell effects remains to be determined.