Leukocytes and interferon in the host response to viral infections. II. Enhanced interferon response of leukocytes from immune animals

Expression of IFN-Gamma is significantly reduced during severity of covid-19 infection in hospitalized patients

Cytokines play an important role in SARS-CoV-2 infection progression and severity. A number of inflammatory cytokines have been directly associated with disease severity including IL-6 (interleukin-6), IL-10, TNF-α (tumor necrosis factor alpha), IFN-γ (interferon-gamma). Here, in this study, the aim was to better understand the interplay between host immune response mediated by cytokines and severity of SARS-CoV-2 infection by assessing cytokine expression. Therefore, we measured expression levels of a total of 12 genes (IFNA-1, IFN-γ, IL-1α, IL-1β, IL-4, IL-6, IL-7, IL-10, IL-11, IL-13, IL-15, and IL-27) encoding inflammatory, anti-inflammatory and regulatory cytokines using QRT-PCR in hospitalized patients with severe infection compared to mildly infected. IFN-γ was identified as a potent marker of disease severity as indicated previously. Moreover, levels of IL-7 were also found to be partially reduced in patients compared to the healthy controls and linked negatively to disease severity. Identification of these cytokines may be helpful in not only understanding disease pathogenesis but also in better management of the patients after covid infection.

Differential roles of interferons in innate responses to mucosal viral infections

Interferons (IFNs) are among the first vertebrate immune pathways activated upon viral infection and are crucial for control of viral replication and dissemination, especially at mucosal surfaces as key locations for host exposure to pathogens. Inhibition of viral establishment and spread at and from these mucosal sites is paramount for preventing severe disease, while concomitantly limiting putative detrimental effects of inflammation. Here, we compare the roles of type I, II, and III IFNs in regulating three archetypal viruses - norovirus, herpes simplex virus, and severe acute respiratory virus coronavirus 2 (SARS-CoV-2) - which infect distinct mammalian mucosal tissues. Emerging paradigms include highly specific roles for IFNs in limiting local versus systemic infection, synergistic activities, and a spectrum of protective versus detrimental effects of IFNs during the infection response.

Biology and pathogenesis of chikungunya virus

Chikungunya virus (CHIKV) is a re-emerging mosquito-borne alphavirus responsible for a recent, unexpectedly severe epidemic in countries of the Indian Ocean region. Although many alphaviruses have been well studied, little was known about the biology and pathogenesis of CHIKV at the time of the 2005 outbreak. Over the past 5 years there has been a multidisciplinary effort aimed at deciphering the clinical, physiopathological, immunological and virological features of CHIKV infection. This Review highlights some of the most recent advances in our understanding of the biology of CHIKV and its interactions with the host.

Migration inhibitory factor and interferon in the circulation of mice with delayed hypersensitivity

When mice infected with Mycobacterium tuberculosis strain BCG were inoculated intravenously with old tuberculin (OT) or living BCG cells, both migration inhibitory factor (MIF) and interferon appeared in the circulation within a few hours. In such animals, which showed delayed hypersensitivity by footpad tests, as little as 1.5 mg of OT or as few as 1.7 x 10(6) bacteria per mouse were capable of eliciting circulating MIF and interferon. Uninfected animals inoculated with large doses of OT or living BCG cells did not produce MIF or interferon. When nonspecific stimuli such as bacterial lipopolysaccharide (LPS; from Salmonella typhimurium strain LT-2), heat-killed Brucella abortus, Newcastle disease virus (NDV), and polyinosinic acid:polycytidilic acid (poly I:C) were inoculated intravenously into BCG-infected mice, MIF was produced in the circulation of animals challenged with LPS or Brucella but not in those challenged with NDV or poly I:C, although all the stimuli were capable of eliciting an interferon response. The interferon elicited in BCG-infected mice by specific antigen differed in at least one important property from the viral inhibitor produced by the nonspecific stimuli. The interferon which appeared after injection of OT or living BCG cells was destroyed by treatment at pH 2 for 24 hr at 4C, whereas the interferons produced after injection of the nonspecific stimuli were stable under the same conditions. The MIF activity in plasma from sensitized mice inoculated with specific antigen was also destroyed by treatment at pH 2. When mouse plasma containing both MIF and interferon activity was filtered through Sephadex G-100, both mediators were excluded in the same peak fractions. Sensitization of mice with complete Freund adjuvant instead of infection with BCG cells produces a different pattern of response. Although hypersensitive to specific antigen by footpad swelling tests, mice sensitized with complete Freund adjuvant failed to produce MIF or interferon when they were inoculated intravenously with OT or living BCG cells.

The interaction of human macrophages and lymphocytes in the phytohemagglutinin-stimulated production of interferon

In studies of 13 normal adults to determine the blood cell types responsible for interferon production induced by phytohemagglutinin, the following observations were made. (a) In cultures containing 96-100% pure macrophages derived from blood monocytes, no interferon was detected in either the presence or the absence of phytohemagglutinin for up to 92 hr. (b) In cultures of 99.5-100% pure lymphocytes, low levels of interferon were detected in the presence, but not in the absence, of phytohemagglutinin. (c) An average fivefold increase in interferon titers occurred when pure lymphocytes were combined with the macrophages in culture with phytohemagglutinin. The peak response of interferon occurred at 68 hr after the initiation of the combined cultures. For maximum response, phytohemagglutinin was required for the duration of the culture, and both cell types in association were necessary. Medium from phytohemagglutinin-stimulated macrophages or lymphocytes could not substitute for the corresponding intact cell. However, frozen-thawed macrophages in combination with lymphocytes and phytohemagglutinin produced an intermediate interferon response. An increase in either cell type produced an increased response in the range studied: lymphocytes, 0.45-1.8 x 10(6) per ml; and macrophages, 0.5-2.1 x 10(5) per ml. Syngeneic fibroblasts, HeLa cells, or mouse macrophages could not substitute for the human macrophages in the combined cultures with phytohemagglutinin. (d) Although all cultures producing interferon showed some degree of transformation (thymidine-(3)H incorporation into deoxyribonucleic acid), no direct correlation between the degree of phytohemagglutinin-induced lymphocyte transformation and the interferon titers was observed.The demonstration of macrophage-lymphocyte interaction in the production of interferon is of interest in view of the known interrelationship of these same cell types in antibody synthesis and cellular immunity.

Potentiating Effect of Freund's Adjuvant on Interferon Production by Endotoxin or Poly rI*Poly rC

Intraperitoneal injection of mice with mineral oil, incomplete (IFA) or complete Freund's adjuvant (CFA) increased the interferon response to endotoxin or (poly rI)*(poly rC) administered intravenously 2 days later. After endotoxin administration, circulating interferon titers were increased at several different times of sampling and with a variety of endotoxin dosages. When injection of endotoxin was delayed until 6 to 8 days after the administration of IFA or CFA, interferon production was markedly decreased. Mice treated with CFA and injected with endotoxin 2 days later became more resistant to intranasal vesicular stomatitis virus challenge than mice injected with endotoxin alone. Hyporeactivity to the interferon-inducing capacity of a second injection of endotoxin 2 days after the first injection could not be overcome by administering CFA simultaneously with the first dose. CFA treatment not only raised the serum interferon titers produced by endotoxin, but also increased the number of interferon-forming cells in the spleen after administration of endotoxin in vivo. In addition, CFA enhanced the intravascular clearance of (poly rI)*(poly rC). The possibility that Freund's adjuvant increased the interferon response to endotoxin and (poly rI)*(poly rC) by stimulating the uptake and processing of the interferon inducer by lymphoreticular cells is discussed.

Characterization of Chikungunya pseudotyped viruses: Identification of refractory cell lines and demonstration of cellular tropism differences mediated by mutations in E1 glycoprotein

Chikungunya virus (CHIKV) is an alphavirus responsible for a number of large outbreaks. Here we describe the efficient incorporation of CHIKV envelope glycoproteins into lentiviral and rhabdoviral particles. Vectors pseudotyped with CHIKV envelope proteins efficiently transduced many cell types from different species. However, hematopoietic cell types were either partially or completely refractory. A mutation in E1 (A226V) has been linked with expansion of tropism for mosquito species, although differences in in vitro infection of mosquito cell lines have not been noted. However, pseudovirion infectivity assays detected subtle differences in infection of mosquito cells, suggesting an explanation for the changes in mosquito tropism. The presence of C-type lectins increased CHIKV pseudotyped vector infectivity, but not infection of refractory cells, suggesting that they act as attachment factors rather than primary receptors. CHIKV pseudotypes will serve as an important tool for the study of neutralizing antibodies and the analysis of envelope glycoprotein functions.

Interferon-gamma: a historical perspective

This article reviews the main lines of thinking and exploration that have led to our current conception of the role of IFN-gamma in immune defense and autoimmunity. In 1965 the first report appeared describing production of an interferon-like virus inhibitor in cultured human leukocytes following exposure to the mitogen phytohemagglutinin. In the early 1970s the active principle became recognized as being distinct from classical virus-induced interferons, leading to its designation as immune interferon or Type II interferon, and eventually IFN-gamma. Up to that point interest in the factor had come almost exclusively from virologists, in particular those among them who were believers in interferon. Evidence first coming forward in the 1980s that IFN-gamma is indistinguishable from macrophage-activating factor (MAF), then a prototype lymphokine, was the signal for immunologists at large to become interested. Today IFN-gamma ranks among the most important endogenous regulators of immune responses.

The biology of chikungunya: a brief review of what we still do not know

Responsible for a massive outbreak in the Indian Ocean in 2005-2006, the chikungunya virus is also reemerging in India where it has already infected over a million persons. Imported cases of the disease are reported in Asia, USA, and Europe, where a small epidemic occurred, due to transmission by local mosquitoes. Chikungunya virus is an alphavirus (Togaviridae family) that usually induces an acute illness characterized by fever, rash, and painful, incapacitating arthralgia a few days after being bitten by an infected mosquito, but recurrent joint pains are frequent. Unusual severe forms of the disease are also being reported that emphasize the importance of close monitoring of arboviruses in more fragile populations, such as the elderly and the newborns. Alphaviruses have generally been studied out of their epidemic context, leading to a large knowledge of their molecular features, and a much narrower understanding of their epidemiology and induced pathogenesis. Deciphering chikungunya virus specific molecular features as well as how the virus interacts with its vector and with its host are key to foresee, prevent and manage future epidemics, as well as prevent, treat or cure chikungunya disease.

Characterization of reemerging chikungunya virus

An unprecedented epidemic of chikungunya virus (CHIKV) infection recently started in countries of the Indian Ocean area, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The basis for chikungunya disease and the tropism of CHIKV remain unknown. Here, we describe the replication characteristics of recent clinical CHIKV strains. Human epithelial and endothelial cells, primary fibroblasts and, to a lesser extent, monocyte-derived macrophages, were susceptible to infection and allowed viral production. In contrast, CHIKV did not replicate in lymphoid and monocytoid cell lines, primary lymphocytes and monocytes, or monocyte-derived dendritic cells. CHIKV replication was cytopathic and associated with an induction of apoptosis in infected cells. Chloroquine, bafilomycin-A1, and short hairpin RNAs against dynamin-2 inhibited viral production, indicating that viral entry occurs through pH-dependent endocytosis. CHIKV was highly sensitive to the antiviral activity of type I and II interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host.

Chikungunya virus (CHIKV) is a reemerging alphavirus responsible for an unprecedented epidemic in countries of the Indian Ocean region, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The most recent epidemic reemergences were documented in Kinshasa, (50,000 estimated cases in 1999–2000), in Indonesia (2001–2003), the Indian Ocean islands of Mayotte, Mauritius, Réunion, and the Seychelles (270,000 cases in 2005–2006 in La Réunion island), and in India (1.4 to 6.5 million estimated cases in 2006–2007). There is a critical lack of knowledge on the biology of CHIKV. In particular, virtually nothing is known about the interaction of CHIKV (and of most alpahaviruses) with human primary cells. We have studied the replication characteristics and the tropism of clinical CHIKV strains from La Réunion. We designed various assays and reagents to follow viral replication, and we report here that adherent cells (epithelial and endothelial cells, primary fibroblasts), as well as macrophages, are sensitive to infection. In contrast, blood cells did not allow viral replication. We also characterized viral entry pathways and sensitivity to interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host. This paper is the result of a collaborative effort between numerous teams from Institut Pasteur, the Groupe Hospitalier Sud Réunion, and other institutions. Our aim was to establish a task force with multiple and complementary expertise on virology, immunology, and cell biology in order to characterize this enigmatic virus.

Cytokine content in pleural effusion. Comparison between tuberculous and carcinomatous pleurisy

Tuberculous pleurisy is a good model for resolution of local cellular immunity. It would be expected that tuberculous pleural fluid contains a variety of immunologically important cytokines because of the accumulation of immunocompetent cells in the pleural cavity. We studied interleukin 1 (IL-1), interleukin 2 (IL-2), and interferon gamma (IFN-gamma) levels in pleural fluid of 20 patients with tuberculous pleurisy and compared them with those in pleural fluid of 20 patients with malignant pleurisy. We also evaluated adenosine deaminase (ADA) levels in both effusions. Tuberculous pleural fluid had higher levels of IL-1, IL-2, IFN-gamma, and ADA than malignant pleural fluid. Although the difference of IL-1 level between tuberculous and malignant pleural fluid was modest, that of IL-2, IFN-gamma, and ADA was dominant. These findings suggest that activated T lymphocytes in tuberculous pleural fluid concern the production of lymphokines at the morbid site and they effectively exert local cellular immunity through the action of such lymphokines.

Cytokine activation of antibacterial activity in human pulmonary macrophages: comparison of recombinant interferon-gamma and granulocyte-macrophage colony-stimulating factor

We examined the ability of two recombinant human cytokines, granulocyte-macrophage colony-stimulating factor (rHu-GM-CSF) and interferon-gamma (rHu-IFN-gamma) to activate antibacterial mechanisms in human pulmonary macrophages (PM) and peripheral blood monocytes (PBM). Growth of Legionella pneumophila (LP) was assessed in PM or PBM which had been exposed to either rHu-IFN-gamma (500-1000 u/ml) or rHu-GM-CSF (1 to 10,000 u/ml). In both PM and PBM exposed to 500 u/ml rHu-IFN-gamma, growth of LP was reduced compared to cells exposed to media alone. By comparison, exposure of these cell types to rHu-GM-CSF had no detectable effect on bacterial replication. In order to investigate potential mechanisms accounting for this observation, the effect of these cytokines on the hydrogen peroxide (H2O2)-releasing capacity of cells was studied. Exposure of PM and PBM to rHu-IFN-gamma (500 to 1000 u/ml) resulted in increased production of H2O2 triggered by phorbol myristate acetate; when subjected to the same experimental conditions, rHu-GM-CSF-exposed cells exhibited no increase in H2O2 production. To further clarify the role of rHu-IFN-gamma-induced augmentation of oxidative metabolism on cellular inhibition of bacterial growth, an amount of catalase capable of completely neutralizing extracellular H2O2 was added to cells before and during infection. This did not abrogate the antibacterial activity of rHu-IFN-gamma. These studies demonstrate that rHu-IFN-gamma but not rHu-GM-CSF is capable of augmenting the capacity of PM and PBM to restrict LP growth. These data suggest that the antibacterial activity of rHu-IFN-gamma in this system may involve oxidative as well as nonoxidative mechanisms.

A unifying model of the immunoregulatory role of the interferon system: can interferon produce disease in humans?

This hypothesis is a presentation of a unifying model of the interferon (IFN) system as a cascade of sequentially interacting responses of IFNs-alpha, -beta, and -gamma involved in modulation of the immune response. We propose that every antigen is an IFNogen. The first stage(s) of immune responsiveness is associated primarily with the production of the family of IFN-alpha. In certain immunologically mediated diseases, including the autoimmune diseases and AIDS, disturbances in the synthesis of IFN-alpha occur with a switch to the production of predominantly acid-labile types, which have a negative immunoregulatory effect. Moreover, disturbances of IFN synthesis in the embryo or fetus can lead to deformities. Some viruses and other biological and chemical substances manifest a pathological effect by the IFN they induce. This IFN may help sustain the viruses and other substances which induce this IFN. We think it is unsafe to give patients immunoregulators in incomplete form. Thus, there is a potential danger in giving patients recombinant forms of IFNs and interleukin 2 produced in bacteria. In certain immune disorders, we may be able to treat patients by the binding or removal of hyperproduced IFNs from the body. This may lead to the restoration of immunologic balance and clinical improvement.

Deficient immune interferon production in tuberculosis

Production of interferon (IFN)-alpha and -gamma by peripheral blood mononuclear cells (PBMC) were studied in 28 patients with active tuberculosis and 28 healthy control subjects matched for age, sex, ethnic origin and diet. No significant differences were found between patients and matched controls in mean titres of IFN-alpha induced by Newcastle disease virus, IFN-gamma induced by staphylococcal enterotoxin A with tetrahydrophorbyl acetate, and IFN-gamma induced by purified protein derivative (PPD). However, a subset of nine out of 25 tuberculosis patients tested produced low titres (less than 100 u/ml) of IFN-gamma in response to PBMC stimulation with PPD. In comparison to other patients, this group was characterized by lower IFN-alpha and IFN-gamma responses to virus and mitogens respectively, relative anergy to tuberculin skin testing, depressed in vitro PBMC proliferative responses to PPD, and neutrophil leucocytosis. In all nine patients effective chemotherapy restored cutaneous reactivity, PBMC proliferative responses, neutrophil counts and IFN-alpha responses to virus by 6 months, and also IFN-gamma responses to PPD in one patient re-tested.

Immunological and chemotherapeutic prevention and control of oncogenic viruses

Computed tomographic (CT) and surgical findings were correlated retrospectively in 51 patients with preoperative diagnoses of prolactin-secreting pituitary microadenomas. Twenty-four had microadenomas at surgery. Twenty-eight had identifiable discrete lesions. Of these, 18 had microadenomas and 10 did not; these two groups could not be distinguished reliably. Six patients with proven microadenomas had normal CT scans. Focal hypodense lesions, sellar floor erosion, infundibulum displacement, gland height greater than 8 mm, and an abnormal diaphragma sellae configuration are neither sensitive nor specific findings of microadenoma. A significant number of patients with proven microadenomas had few or none of these abnormalities. Thus, recognition of prolactin microadenoma is seldom possible by CT alone, even with high-resolution direct coronal imaging.

Identification of interferon-gamma as the lymphokine that activates human macrophage oxidative metabolism and antimicrobial activity

Human blood mononuclear leukocytes stimulated with toxoplasma antigen, concanavalin A, mezerein plus lentil lectin, or staphylococcal enterotoxin A secreted a factor (macrophage-activating factor, or MAF) that enhanced the capacity of human macrophages to release H2O2 and to kill toxoplasmas. The same lymphoid supernatants contained IFN gamma but not IFN alpha or IFN beta. The MAF activity of six of seven unfractionated supernatants was completely eliminated by a monoclonal antibody that neutralizes IFN gamma, and MAF in the remaining supernatant was almost completely neutralized. Native IFN gamma partially purified by two independent protocols to specific activities of 1 X 10(6) and 10(7) U/mg protein was enriched in MAF activity at least as much as in antiviral activity. The capacity of macrophages to secrete H2O2 after incubation in partially purified native IFN gamma (mean peak stimulation, 8.8-fold) was greater than with unpurified lymphokines (3.8-fold) and sometimes equaled or exceeded the capacity of freshly harvested monocytes. The MAF activity of the partially purified native IFN gamma preparations was abolished by monoclonal anti-IFN gamma. Finally, IFN gamma of greater than 99% estimated purity was isolated (at Genentech, Inc.) from bacteria transformed with the cloned human gene for this lymphokine. Recombinant IFN gamma had potent MAF activity, stimulating the peroxide-releasing capacity of macrophages an average of 19.8-fold at peak response and enhancing their ability to kill toxoplasmas from 2.6 +/- 1.3% for untreated cells to 54 +/- 0.4% for treated cells. Attainment of 50% of the maximal elevation in peroxide-releasing capacity required a geometric mean concentration of 0.1 antiviral U/ml of recombinant IFN gamma, which is estimated to be approximately 6 picomolar for this preparation. Peroxide secretory capacity and toxoplasmacidal activity of macrophages peaked 2-4 d after exposure to IFN gamma. Peroxide-secretory capacity remained elevated during at least 6 d of continuous exposure, but the effect of IFN gamma was reversed within about 3 d of its removal. Activation was usually but not invariably accompanied by characteristic changes in cell morphology. Thus, IFN gamma activates human macrophage oxidative metabolism and antimicrobial activity, and appeared to be the only factor consistently capable of doing so in the diverse LK preparations tested.

Immune interferon produced in vitro as a quantitative indicator of cell-mediated immunity

The present study was constructed to provide some information on the possibility of utilizing immune interferon as a quantitative indicator of cell-mediated immunity and to clarify some of the nature of immune interferon-producing cells (IIPC). When spleen cells derived from L cell-sensitized mice were co-cultivated with L cells, interferon appeared in the culture fluid. It was shown by additional experiments that the cells responsible for immune interferon production in this system were T-lymphocytes assisted by macrophages. The pattern of kinetics of immune interferon production in vitro was similar to that of migration inhibitory factor or T cell-mediated cytotoxicity.

Abortive replication of vaccinia virus in activated rabbit macrophages

During the course of infection of rabbits with vaccinia virus, macrophages obtained from the peritoneal cavity develop bactericidal activity and the replication of vaccinia virus becomes restricted in these cells. The abortive replication of vaccinia virus in the activated macrophages was characterized in the present study. The virus adsorbed to and was uncoated equally well in macrophages from both normal and infected rabbits. A burst of deoxyribonucleic acid synthesis of comparable magnitude took place 3 to 6 h after infection in both normal and activated macrophages. Although the production of viral antigens, as detected by immunodiffusion and immunofluorescence, was the same in both types of cells, very few virus particles were formed in activated as compared with normal macrophages. We conclude that a block in a late step of the virus replication cycle occurred in the activated macrophages.

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.

Anti-viral activity induced by culturing lymphocytes with tumor-derived or virus-transformed cells. Identification of the anti-viral activity as interferon and characterization of the human effector lymphocyte subpopulation

A viral inhibitor(s) is released in the supernate of mixed cultures containing human or mouse lymphocytes and cells from certain lines. The inhibitor is active against a variety of unrelated viruses and is a protein that is not toxic for cells. It does not inactivate viruses directly, but inhibits viral replication through an intracellular mechanism that involves synthesis by the cells of both RNA and protein. These characteristics identify the inhibitor as an interferon. The anti-viral activity is contained in at least two molecular species, of approximately 25,000 and 45,000 daltons, respectively. In addition to the anti-viral activity, the supernates of the mixed cultures display an anti-cellular activity, the inhibition of DNA synthesis and of cell multiplication. The anti-viral and the anti-cellular activities are positively correlated in supernates from various cultures and in partially purified preparations. The human cell population responsible for interferon production is composed mainly of Fc-receptor positive, surface immunoglobulin negative, non-T-cell lymphocytes. The ability of certain cell lines to induce interferon seems to be preferentially associated with tumor origin or with in vitro transformation by certain viruses (Epstein-Barr virus, murine sarcoma virus).

Studies on the capacity of human tonsillar lymphocyte subpopulations to produce interferon

Tonsillar lymphocytes produced classical interferon (Type I) in response to NDV infection and produced immune interferon (Type II) in response to PHA, PPD or histo-incompatible antigens. Lymphocytes having higher specific gravity and having a greater proliferative response to mitogens or antigens produced more interferon than lymphocytes having lower specific gravity. There was no difference between heavy and light small tonsillar lymphocytes in regard to their sensitivity to the protective effects of interferon. As for the interferon produced in association with a cellular immune response, the peak of interferon production tended to appear earlier than the peak of 3H-TdR incorporation. It is suggested that tonsillar lymphocytes play an important role in human host defense against virus infections.

Interferon: an inducer of macrophage activation by polyanions

Purified mouse fibroblast interferon (IF) directly rendered resting macrophages tumoricidal. The physicochemical properties and species specificity of the stimulatory agent fall within the present definition of IF. Since a number of polyanions induce macrophage IF, the antitumor and antimicrobial activities may result from the ability of newly released IF to modify macrophage activity.

Interferon-producing capacity of germfree mice

The general capacity of germfree mouse spleen cells to produce interferon in vitro in response to various stimuli was investigated. The interferon response of germfree mouse spleen cells in vitro, when compared with that of the conventionals, appears to be lower to some inducers. Interferon production in vitro stimulated by hemagglutinating virus of Japan (HVJ) or BHK-HVJ cells (BHK cells persistently infected with HVJ) was apparently suppressed in germfree mouse spleen cells as compared with the corresponding conventionals, whereas no difference of interferon production was observed between germfree and conventional mouse spleen cells in response to Newcastle disease virus, Escherichia coli endotoxin, poly(I:C), and phytohemagglutinin. Although monocontamination with HVJ had no enhancing effect on the interferon-producing ability of germfree mouse spleen cells in response to HVJ, conventionalization for 2 weeks greatly enhanced interferon-producing capacity.

Mechanism of induction of cell-mediated immunity to virus infections: in vitro inhibition of intracellular multiplication of mouse adenovirus by immune spleen cells

Mice were protected from lethal infection with mouse adenovirus (M-Ad) by adoptive transfer of immune spleen cells (ISC) that were prepared from mice immunized with M-Ad and not protected by sonicated ISC. However, a similar extent of protection was also observed by passive immunization with anti-M-Ad serum. In contrast, by in vitro experiments ISC were shown to be able to interrupt intracellular multiplication of M-Ad, whereas sonicated ISC, unimmunized mouse spleen cells, or anti-M-Ad serum were unable to do so. ISC were inhibitory in vitro when added within 12 h postinfection but not when added later. The inhibitory activity of ISC was regarded as due to cell killing by ISC, since the trypan blue exclusion test showed that above 80% of infected cells were killed by ISC even when 5'-fluorodeoxyuridine was added to the cells to block viral deoxyribonucleic acid synthesis, under which conditions control infected cells, to which ISC were not added or normal spleen cells were added, were kept alive at least for a few days. Kinetics studies in M-Ad-infected mice showed that the inhibitory activity of ISC became highest at 1 to 2 weeks postinfection and faded away thereafter in a few weeks, whereas serum antibody titer assayed by passive hemagglutination reached its peak level at about 4 weeks postinfection and declined gradually therafter.

The protective role of thymus-derived lymphocytes in arbovirus-induced meningoencephalitis

The inflammatory response in mouse brain and the elimination of virus from the brain following intracerebral inoculation of a group A arbovirus has been shown to be T-cell dependent. Virus persists in the brain of T-cell depleted mice, and inflammation is depressed. Virus persists in the brain of T-cell depleted mice, and inflammation is depressed. Inflammation is restored by transfer of immune cells but not by immune serum, and the transferred cells are effective in reducing virus titres in the absence of circulating antibody. Transferred antibody is not efficient in protecting infected mice. The cells that restore inflammation can come from mice immunized with a group A arbovirus of the same subtype but not from mice immunized with more distantly related viruses. Macrophages may be important effector cells working in collaboration with T cells.

Cellular immunity to herpes simplex virus mediated by interferon

Rabbit kidney cell monolayers infected with herpes simplex virus (HSV) were incubated with leukocytes from rabbits immunized with complete Freund's adjuvant. When the leukocytes were exposed to tuberculin purified protein derivative (PPD), viral replication and plaque formation were markedly inhibited. Similarly, when leukocytes from animals immunized with HSV were exposed to UV-inactivated HSV, viral replication was markedly inhibited. Exposure of leukocytes from unimmunized animals or animals immunized with incomplete Freund's adjuvant to UV-inactivated virus or PPD produced relatively little inhibition of viral replication. Examination of supernatant fluids from stimulated cultures revealed a soluble mediator that had the properties of interferon. Interferon production was detected within several hours after exposure of sensitized leukocytes to antigen. Supernatant fluids from as few as one sensitized leukocyte per 200 rabbit kidney cells inhibited HSV replication by over 90%. These findings support the concept that the cellular immune response to HSV consists of two phases: an immunologically specific antigen recognition phase, and a nonspecific effector phase that stops HSV spread by generating interferon.

Interferon production by macrophages from adult and newborn rabbits bearing fibroma virus-induced tumors

Tumors were induced in adult and newborn rabbits by inoculation of fibroma virus. After 10 to 14 days, oil-induced peritoneal macrophages were harvested, purified, and tested in vitro for interferon synthesis after stimulation with specific and nonspecific viruses. Peritoneal macrophages from adult rabbits that had initiated tumor regression produced high levels of interferon (titers ranged from 160 to 640) after stimulation with fibroma virus, whereas macrophages from normal adult rabbits failed to produce significant levels of interferon under the same conditions (titers ranged from <10 to 10). Furthermore, fibroma-immune macrophages responded to vaccinia virus and Newcastle disease virus with higher levels of interferon than did normal macrophages. In contrast, macrophages from newborn tumor-bearing rabbits that showed no evidence of tumor regression failed to respond to fibroma virus stimulation with higher levels of interferon (titers ranged from <10 to 10). These macrophages did, however, yield significantly more interferon than newborn control macrophages when stimulated with a good interferon inducer, Newcastle disease virus (titers ranged from 10 to 80). These data suggest that interferon production may be an expression of macrophage activation to fibroma antigens and that macrophage activation is impaired in newborn rabbits with progressive growing tumors.

Selective decrease in interferon production in immunotolerant mice

Mice, immunologically unresponsive to Newcastle disease virus, were impaired in their capacity to produce interferon when induced with Newcastle disease virus, but not when induced with an unrelated virus.

Stimulation of transplantation immunity and plasma cell reaction by interferon in mice

It is assumed that interferon is a necessary component of the formation of immunological reactivity. At the same time interferon may serve as a factor stimulating immunity as a whole.

Administration of interferon to mice, recipients of skin allografts, brings about acceleration of rejection process and stimulation of the cytotoxic activity of lymphocytes of mice towards target cells. With the repeated transplantations to mice treated with interferon in the first grafting, acceleration of rejection of new grafts (the `second set' phenomenon) is observed.

Intrasplenic inoculation of interferon to mice at the time of antigen administration results in intensified plasma cell reaction in the spleens.

Enhanced effect of repeated administration of bacterial vaccine against viral respiratory infection

Administration of a standard bacterial vaccine (SBV) affords some protection against influenza infection in mice if given 4 to 5 h before inoculation of the virus. This effect was enhanced by repeated injections of SBV 7 and 14 days earlier, as measured by the length of survival, mortality rate, development of gross pneumonia, and virus multiplication in the lungs. Serum interferon levels were likewise enhanced by immunization with SBV, which may, at least in part, explain the increased preventive effect.

Chlorite-oxidized amylose as an adjuvant for interferon production

Chlorite-oxidized amylose (COAM), when given intraperitoneally to mice and to cats, increased the titer of serum interferon subsequently induced by polyinosinic.polycytidylic acid (In.Cn). Increases ranged from 6- to 100-fold. Maximal effect was observed when COAM was given 3 h prior to In.Cn. COAM given intravenously prior to Newcastle disease virus also significantly increased serum interferon titers.

Selective increase in lymphocyte interferon response to vaccinia antigen after revaccination

Viral antigen prepared by heat inactivation of vaccinia virus stimulated production of interferon in association with transformation of sensitized human lymphocytes in vitro. Involvement of a macrophage-lymphocyte interaction in production of interferon stimulated by viral antigen was found in which macrophage greatly augmented the amount of interferon produced by lymphocytes. Reimmunization with live vaccinia virus resulted in a selective increase in the ability of lymphocytes to produce interferon in the presence of viral antigen 4-7 weeks later without a corresponding increase in the degree of already significant lymphocyte transformation. There was no correlation between the extent of lymphocyte transformation and the amount of interferon produced. The augmented interferon response after reimmunization described in this study may be a significant component of the protective effect of immunization with vaccinia against disease occurring after exposure to small-pox.

Specific macrophage immunity to vaccinia virus: macrophage-virus interaction

Macrophage immunity to vaccinia virus was examined by measuring replication of vaccinia virus in immune and nonimmune rabbit peritoneal macrophages. Vaccinia virus multiplied in macrophages from normal rabbits but failed to replicate in macrophages from immune rabbits. The specificity of vaccinia restriction was demonstrated by the ability of myxoma virus to replicate in nonimmune and vaccinia-immune macrophages. Vaccinia virus absorbed equally well to immune and nonimmune macrophages, but only a small fraction of immune cells supported synthesis of virus antigen. Virus eclipse and infective center neutralization studies suggested that much of the virus remained at the plasma membrane of immune macrophages, even after prolonged incubation in culture. These data support our previous suggestions that macrophages may contribute to specific immunity against vaccinia virus.

Interferon in nasal secretions and sera of calves after intranasal administration of avirulent infectious bovine rhinotracheitis virus: association of interferon in nasal secretions with early resistance to challenge with virulent virus

Calves which had received avirulent infectious bovine rhinotracheitis virus (AV-IBR) by intranasal (IN) administration developed detectable levels of interferon (IF) in nasal secretions as early as 40 hr later. Peak titers (1:640) of IF appeared in secretions 72 to 96 hr after administration of virus, and titers of 1:80 to 1:320 were maintained through the 8th day. Lower titers (1:5 to 1:10) of IF were detected in sera obtained on the 4th to 8th days after administration of virus. Peak titers of IF in respiratory tract secretions were accompanied by a 100- to > 1,000-fold reduction in the levels of AV-IBR present in the secretions. Serum antibody was not detected prior to the 8th day after administration of AV-IBR. Calves which received AV-IBR by the IN route 72 or 96 hr earlier were refractory to challenge with virulent infectious bovine rhinotracheitis virus (IBR), whereas calves receiving AV-IBR 18 or 40 hr earlier became clinically ill following challenge. The temporal association between appearance of IF in respiratory tract secretions and onset of protection against challenge suggests a cause and effect relationship. No IF was detected in either nasal secretions or sera of calves receiving modified IBR virus by intramuscular injection. Following subsequent IN challenge of these calves, IF was detected in nasal secretions as early as 24 hr postchallenge and was maintained at titers of 1:40 to 1:80 for approximately 4 days, even in the absence of virus recovery. Greater ease of local IF induction with IBR virus in calves previously sensitized with that virus is suggested.