EFFECT OF CORTISONE OF GENETIC RESISTANCE TO MOUSE HEPATITIS VIRUS IN VIVO AND IN VITRO

Human Amniotic Fluid Stem Cells Ameliorate Thioglycollate-Induced Peritonitis by Increasing Tregs in Mice

Mesenchymal stem cells (MSCs) affect immune cells and exert anti-inflammatory effects. Human amniotic fluid stem cells (hAFSCs), a type of MSCs, have a high therapeutic effect in animal models of inflammation-related diseases. hAFSCs can be easily isolated and cultured from amniotic fluid, which is considered a medical waste. Hence, amniotic fluid can be a source of cells for MSC therapy of inflammatory diseases. However, the effect of hAFSCs on acquired immunity in vivo, especially on regulatory T cells, has not yet been fully elucidated. Therefore, in this study, we aimed to understand the effects of hAFSCs on acquired immunity, particularly on regulatory T cells. We showed that hAFSCs ameliorated the thioglycollate-induced inflammation by forming aggregates with host immune cells, such as macrophages, T cells, and B cells in the peritoneal cavity. Further, the regulatory T cells increased in the peritoneal cavity. These results indicated that, in addition to helping the innate immunity, hAFSCs could also aid the acquired immune system in vivo against inflammation-related diseases by increasing regulatory T cells.

Beneficial effect of combinational methylprednisolone and remdesivir in hamster model of SARS-CoV-2 infection

Effective treatments for coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) are urgently needed. Dexamethasone has been shown to confer survival benefits to certain groups of hospitalized patients, but whether glucocorticoids such as dexamethasone and methylprednisolone should be used together with antivirals to prevent a boost of SARS-CoV-2 replication remains to be determined. Here, we show the beneficial effect of methylprednisolone alone and in combination with remdesivir in the hamster model of SARS-CoV-2 infection. Treatment with methylprednisolone boosted RNA replication of SARS-CoV-2 but suppressed viral induction of proinflammatory cytokines in human monocyte-derived macrophages. Although methylprednisolone monotherapy alleviated body weight loss as well as nasal and pulmonary inflammation, viral loads increased and antibody response against the receptor-binding domain of spike protein attenuated. In contrast, a combination of methylprednisolone with remdesivir not only prevented body weight loss and inflammation, but also dampened viral protein expression and viral loads. In addition, the suppressive effect of methylprednisolone on antibody response was alleviated in the presence of remdesivir. Thus, combinational anti-inflammatory and antiviral therapy might be an effective, safer and more versatile treatment option for COVID-19. These data support testing of the efficacy of a combination of methylprednisolone and remdesivir for the treatment of COVID-19 in randomized controlled clinical trials.

The Role of Host Genetic Factors in Coronavirus Susceptibility: Review of Animal and Systematic Review of Human Literature

The SARS-CoV-2 pandemic raises many scientific and clinical questions. These include how host genetic factors affect disease susceptibility and pathogenesis. New work is emerging related to SARS-CoV-2; previous work has been conducted on other coronaviruses that affect different species. We reviewed the literature on host genetic factors related to coronaviruses, systematically focusing on human studies. We identified 1,832 articles of potential relevance. Seventy-five involved human host genetic factors, 36 of which involved analysis of specific genes or loci; aside from one meta-analysis, all were candidate-driven studies, typically investigating small numbers of research subjects and loci. Three additional case reports were described. Multiple significant loci were identified, including 16 related to susceptibility (seven of which identified protective alleles) and 16 related to outcomes (three of which identified protective alleles). The types of cases and controls used varied considerably; four studies used traditional replication/validation cohorts. Among other studies, 30 involved both human and non-human host genetic factors related to coronavirus, 178 involved study of non-human (animal) host genetic factors related to coronavirus, and 984 involved study of non-genetic host factors related to coronavirus, including involving immunopathogenesis. Previous human studies have been limited by issues that may be less impactful now, including low numbers of eligible participants and limited availability of advanced genomic methods; however, these may raise additional considerations. We outline key genes and loci from animal and human host genetic studies that may bear investigation in the study of COVID-19. We also discuss how previous studies may direct current lines of inquiry.

The Role of Host Genetic Factors in Coronavirus Susceptibility: Review of Animal and Systematic Review of Human Literature

BACKGROUND

The recent SARS-CoV-2 pandemic raises many scientific and clinical questions. One set of questions involves host genetic factors that may affect disease susceptibility and pathogenesis. New work is emerging related to SARS-CoV-2; previous work has been conducted on other coronaviruses that affect different species.

OBJECTIVES

We aimed to review the literature on host genetic factors related to coronaviruses, with a systematic focus on human studies.

METHODS

We conducted a PubMed-based search and analysis for articles relevant to host genetic factors in coronavirus. We categorized articles, summarized themes related to animal studies, and extracted data from human studies for analyses.

RESULTS

We identified 1,187 articles of potential relevance. Forty-five studies were related to human host genetic factors related to coronavirus, of which 35 involved analysis of specific genes or loci; aside from one meta-analysis on respiratory infections, all were candidate-driven studies, typically investigating small number of research subjects and loci. Multiple significant loci were identified, including 16 related to susceptibility to coronavirus (of which 7 identified protective alleles), and 16 related to outcomes or clinical variables (of which 3 identified protective alleles). The types of cases and controls used varied considerably; four studies used traditional replication/validation cohorts. Of the other studies, 28 involved both human and non-human host genetic factors related to coronavirus, 174 involved study of non-human (animal) host genetic factors related to coronavirus, 584 involved study of non-genetic host factors related to coronavirus, including involving immunopathogenesis, 16 involved study of other pathogens (not coronavirus), 321 involved other studies of coronavirus, and 18 studies were assigned to the other categories and removed.

KEY FINDINGS

We have outlined key genes and loci from animal and human host genetic studies that may bear investigation in the nascent host genetic factor studies of COVID-19. Previous human studies to date have been limited by issues that may be less impactful on current endeavors, including relatively low numbers of eligible participants and limited availability of advanced genomic methods.

Effect of Orally Administered Atractylodes macrocephala Koidz Water Extract on Macrophage and T Cell Inflammatory Response in Mice

The rhizome of Atractylodes macrocephala Koidz (AM) is a constituent of various Qi booster compound prescriptions. We evaluated inflammatory responses in macrophages and T cells isolated from mice following oral administration of AM water extract (AME). Peritoneal exudate cells were isolated from thioglycollate-injected mice and alterations in scavenger receptors were examined. Peritoneal macrophages were stimulated with lipopolysaccharide (LPS). Serum cytokine responses to intraperitoneal LPS injection were also evaluated. Splenocytes were isolated and their composition and functional responses were measured. The content of atractylenolide I and atractylenolide III, known anti-inflammatory ingredients, in AME was 0.0338 mg/g extract and 0.565 mg/g extract, respectively. AME increased the number of SRA(+)CD11b(+) cells in response to thioglycollate. Peritoneal macrophages isolated from the AME group showed no changes in inflammatory markers such as tumor necrosis factor- (TNF-) α, interleukin- (IL-) 6, inducible nitric oxide synthase, and cyclooxygenase-2 but exhibited a decrease in CD86 expression. Interestingly, AME decreased the serum levels of TNF-α and IL-6 upon intraperitoneal injection of LPS. Regarding the adaptive immune system, AME increased the CD4(+) T cell population and major histocompatibility complex class II molecule expression in the spleen, and cultured splenocytes from the AME group showed increased production of IL-4 concurrent with decreased interferon-γ production during T cell activation. AME promoted the replenishment of peritoneal macrophages during the inflammatory response but its anti-inflammatory activity did not appear to be mediated by the modulation of macrophage activity. AME also altered the immune status of CD4 T cells, promoting the Th2 response.

Contribution of Lewis X Carbohydrate Structure to Neuropathogenic Murine Coronaviral Spread

Although Lewis X (Le(x)), a carbohydrate structure, is involved in innate immunity through cell-to-cell and pathogen recognition, its expression has not been observed in mouse monocytes/macrophages (Mo/Mas). The Mo/Mas that infiltrate the meninges after infection with the neuropathogenic murine coronavirus strain srr7 are an initial target of infection. Furthermore, higher inflammatory responses were observed in gene-manipulated mice lacking α1,3-fucosyltransferase 9, which determines the expression of the Le(x) structure, than in wild type mice after infection. We investigated Le(x) expression using CD11b-positive peritoneal exudate cells (PECs) and found that Le(x) is inducible in Mo/Mas after infection with srr7, especially in the syncytial cells during the late phase of infection. The number of syncytial cells was reduced after treatment of the infected PECs with anti-Le(x) antibody, during the late phase of infection. In addition, the antibody treatment induced a marked reduction in the number of the infected cells at 24 hours post inoculation, without changing the infected cell numbers during the initial phase of infection. These data indicate that the Le(x) structure could play a role in syncytial formation and cell-to-cell infection during the late phase of infection.

The G2019S LRRK2 mutation increases myeloid cell chemotactic responses and enhances LRRK2 binding to actin-regulatory proteins

The Leucine rich repeat kinase 2 (LRRK2) gene is genetically and biochemically linked to several diseases that involve innate immunity. LRRK2 protein is highly expressed in phagocytic cells of the innate immune system, most notably in myeloid cells capable of mounting potent pro-inflammatory responses. Knockdown of LRRK2 protein in these cells reduces pro-inflammatory responses. However, the effect of LRRK2 pathogenic mutations that cause Parkinson's disease on myeloid cell function is not clear but could provide insight into LRRK2-linked disease. Here, we find that rats expressing G2019S LRRK2 have exaggerated pro-inflammatory responses and subsequent neurodegeneration after lipopolysaccharide injections in the substantia nigra, with a marked increase in the recruitment of CD68 myeloid cells to the site of injection. While G2019S LRRK2 expression did not affect immunological homeostasis, myeloid cells expressing G2019S LRRK2 show enhanced chemotaxis both in vitro in two-chamber assays and in vivo in response to thioglycollate injections in the peritoneum. The G2019S mutation enhanced the association between LRRK2 and actin-regulatory proteins that control chemotaxis. The interaction between G2019S LRRK2 and actin-regulatory proteins can be blocked by LRRK2 kinase inhibitors, although we did not find evidence that LRRK2 phosphorylated these interacting proteins. These results suggest that the primary mechanism of G2019S LRRK2 with respect to myeloid cell function in disease may be related to exaggerated chemotactic responses.

Heme oxygenase-2 deletion impairs macrophage function: implication in wound healing

Heme oxygenase (HO)-2 deficiency impairs wound healing and exacerbates inflammation following injury. We examine the impact of HO-2 deficiency on macrophage function and the contribution of macrophage HO-2 to inflammatory and repair responses to injury. Corneal epithelial debridement was performed in control and macrophage-depleted HO-2(-/-) and wild-type (WT) mice and in bone marrow chimeras. Peritoneal macrophages were collected for determination of phagocytic activity and classically activated macrophage (M1)-alternatively activated macrophage (M2) polarization. Depletion of macrophages delayed corneal healing (13.2%) and increased neutrophil infiltration (54.1%) by day 4 in WT mice, whereas in HO-2(-/-) mice, it did not worsen the already impaired wound healing and exacerbated inflammation. HO-2(-/-) macrophages displayed an altered M1 phenotype with no significant expression of M2 or M2-like activated cells and a 31.3% reduction in phagocytic capacity that was restored by inducing HO-1 activity or supplementing biliverdin. Macrophage depletion had no effect, whereas adoptive transfer of WT bone marrow improved wound healing (34% on day 4) but did not resolve the exaggerated inflammatory response in HO-2(-/-) mice. These findings indicate that HO-2-deficient macrophages are dysfunctional and that macrophage HO-2 is required for proper macrophage function but is insufficient to correct the impaired healing of the HO-2(-/-) cornea, suggesting that corneal epithelial expression of HO-2 is a key to resolution and repair in wound healing.

Changes in polysialic acid expression on myeloid cells during differentiation and recruitment to sites of inflammation: role in phagocytosis

Polysialic acid (polySia) is a unique linear homopolymer of α2,8-linked sialic acid that has been studied extensively as a posttranslational modification of neural cell adhesion molecule in the central nervous system. Only two proteins are known to be polysialylated in cells of the immune system: CD56 on human natural killer cells and murine bone marrow (BM) leukocytes, and neuropilin-2 (NRP-2) on dendritic cells (DCs). We tested the hypothesis that polySia expression is regulated during maturation and migration of leukocytes and plays a role in functional activity. Using wild-type and NCAM(-/-) mice, we show that BM neutrophils express only polysialylated CD56, whereas a subset of BM monocytes expresses polysialylated CD56 and/or another polysialylated protein(s). We demonstrate that polysialylated CD56 expression is progressively down-regulated in wild-type monocytes and monocyte-derived cells during migration from BM through peripheral blood to pulmonary and peritoneal sites of inflammation. Freshly isolated monocyte-derived peritoneal macrophages are devoid of polySia yet re-express polySia on NRP-2 and an additional protein(s) after maintenance in culture. Removal of polySia from these cells enhances phagocytosis of Klebsiella pneumoniae, suggesting that down-regulation of polySia on macrophages facilitates bacterial clearance. Using wild-type and NRP-2(-/-) mice, we demonstrate that NRP-2 and an additional protein(s) are polysialylated by ST8 SiaIV in BM-derived DCs. We conclude that polySia expression in monocyte-derived cells is dynamically regulated by ST8 SiaIV activity and by expression of carrier proteins during recruitment to sites of inflammation and influences cellular interactions with microbes, contributing to innate and adaptive immune responses.

Eosinophil contamination of thioglycollate-elicited peritoneal macrophage cultures skews the functional readouts of in vitro assays

Thioglycollate-elicited peritoneal cells are a common source of macrophages for various in vitro assays, including stimulation with TLR ligands, cell signaling assays, phagocytosis, toxicology studies, and cytokine/chemokine production. The most common method for enrichment of cultured thioglycollate-elicited peritoneal cells is adherence. However, the presence of other cell types in freshly isolated and cultured thioglycollate-elicited peritoneal cells has not been examined. Here, we demonstrate that thioglycollate-elicited peritoneal cavity contains 55-60% nonmacrophage cells, and even after adherence, there are still 12-20% nonmacrophage cells remaining. Excluding macrophages, eosinophils are the major cell type in the freshly elicited cavity (30-40%). Eosinophils are also the major cell type contaminating in vitro cultures of thioglycollate-elicited peritoneal macrophages. Moreover, the contamination of macrophage cultures by eosinophils significantly diminishes activation of p38 MAPK and the serine threonine kinase Akt and production of proinflammatory cytokines in response to LPS stimulation. Taken together, these data suggest that thioglycollate-elicited peritoneal cells are far more heterogeneous than reported previously. Further, a failure to remove contaminating eosinophils may greatly affect the interpretation of results obtained with cultured thioglycollate-elicited macrophages. Thus, our data indicate that future studies intent on accurately assessing cultured macrophage phenotype and activation require depletion of all cocontaminating cells, especially eosinophils.

Glycation products in aged thioglycollate medium enhance the elicitation of peritoneal macrophages

Thioglycollate medium (TGM) is widely used as a stimulatory agent to induce non-infectious peritoneal inflammation for elicitation of macrophages from mice and rats. It has been known for a long time that aged, autoclaved TGM is more efficient than freshly prepared TGM, however, the mechanism responsible for this enhanced activity of aged TGM remains obscure. The aging of TGM apparently favors the non-enzymatic reactions between proteins and reducing sugars in TGM that may lead to the generation of advanced glycation endproducts (AGEs). We have found that aged TGM contains 40-fold more AGEs than fresh TGM. The formation of AGEs in TGM was completely blocked by co-incubation with an AGE inhibitor, aminoguanidine. Intraperitoneal injection of aged TGM into rats elicited approximately 2-fold more macrophages than fresh TGM. However, the addition of AGE-modified proteins to fresh TGM increased the yield of peritoneal cells to a level which was significantly higher than both fresh and aged TGM. The injection of AGE-modified proteins alone did not elicit significantly more macrophages than the level of resident peritoneal cells. These results suggest that the formation of AGEs during aging of TGM is responsible for the enhanced macrophage-eliciting activity in aged TGM. AGEs may act as an enhancing agent to augment the existing inflammatory responses. AGE-supplemented TGM may provide an efficient method for eliciting peritoneal macrophages or establishing an inflammatory animal model.

Loss of resistance to murine hepatitis virus strain 3 infection after treatment with corticosteroids is associated with induction of macrophage procoagulant activity

Activation of the immune coagulation system has been implicated in the pathogenesis of liver injury following infection of inbred mice with murine hepatitis virus strain 3 (MHV-3). Following MHV-3 infection, macrophages isolated from MHV-3-susceptible and -semisusceptible inbred strains of mice express increased procoagulant activity (PCA), whereas macrophages from resistant strains express no increase in PCA over basal levels. The PCA induced by MHV-3 is a prothrombinase, encoded by the gene Fgl-2, which encodes a fibrinogen-like protein (musfiblp). In this study, MHV-3-resistant A/J mice treated with methylprednisolone prior to infection with MHV-3 developed elevated levels of alanine aminotransferase in serum and died within 10 days of infection, with histological findings of fulminant hepatitis. In vitro, macrophages isolated from A/J mice and pretreated with methylprednisolone produced a marked increase in functional PCA following infection with MHV-3. The PCA was shown to be a prothrombinase by its ability to cleave 125I-prothrombin. Northern blot analysis of RNA transcripts from these macrophages demonstrated increased transcription of the Fgl-2 gene relative to that in macrophages which had not been pretreated with methylprednisolone prior to MHV-3 infection. Methylprednisolone pretreatment of MHV-3-infected macrophages stabilized the Fgl-2 mRNA. Thus, loss of resistance to MHV-3 secondary to methylprednisolone therapy is associated with increased transcription and stability of Fgl-2 mRNA resulting in expression of the Fgl-2 gene product, musfiblp. These results provide further insight into mechanisms of PCA regulation in response to MHV-3 infection in inbred strains of mice.

Treatment of resistant A/J mice with methylprednisolone (MP) results in loss of resistance to murine hepatitis strain 3 (MHV-3) and induction of macrophage procoagulant activity (PCA)

BALB/cJ mice die of fulminant hepatitis within 7 days of exposure to murine hepatitis virus strain 3 (MHV-3) whereas A/J mice are fully resistant to the lethal effects of MHV-3 infection. Previous studies have implicated macrophage activation with production of a unique macrophage prothrombinase (PCA) and lymphocyte cytokine secretion in the pathogenesis of MHV-3 susceptibility and have demonstrated that immunosuppression induces susceptibility in resistant mice. This study was undertaken to determine whether macrophages, derived from resistant A/J mice and treated in vitro with methylprednisolone sodium succinate (MP), elaborated PCA following MHV-3 exposure and whether therapy with MP altered resistance of A/J mice to MHV-3 infection in vivo. Macrophages, incubated with MP in vitro, expressed dose dependent increases in PCA following infection with MHV-3. No induction of PCA occurred in macrophages treated with MHV-3 or MP alone. Analysis of mRNA transcripts for mouse fibrinogen like protein (musfiblp), the MHV-3 specific prothrombinase, in macrophages which were incubated with MP prior to exposure to MHV-3 demonstrated significantly increased mRNA levels as compared to macrophages not incubated with MP prior to MHV-3 exposure. In vivo, A/J mice treated for 3 days with 500 mg/kg/day of MP prior to infection with MHV-3 demonstrated extensive hepatocyte necrosis and fibrin deposition in hepatic sinusoids on histological examination of liver tissue, elevated serum transaminases and 100% mortality within 10 days of infection. These results therefore provide further support for the role of increased PCA in the pathogenesis of MHV-3 related liver necrosis.

Intrathymic presentation by dendritic cells and macrophages: their role in selecting T cells with specificity for internal and external nominal antigen

The present study focused on the question of whether intrathymic dendritic cells and macrophages (DC/M phi) are involved in the processes of T-cell repertoire selection and establishment of tolerance towards nominal antigen. Proliferation of thymocytes (TC) was determined under limiting dilution (LD) conditions after depletion of DC/M phi and after reconstitution of TC, which were depleted of cells expressing major histocompatibility complex (MHC) class II antigens, with thymic DC/M phi. Trinitrophenyl (TNP) [coupled to ovalbumin (OVA)] was used as an internal antigen in prenatally trinitrobenzenesulphonic acid (TNBS)-treated mice and as an external antigen in prenatally untreated mice. Intrathymic DC/M phi were clearly involved in selecting the repertoire of T cells specific for external antigen: they presented the antigen and initiated proliferation of thymic T cells, which were depleted of MHC class II antigen-expressing cells. But they were not the only cells to present nominal antigen in the thymic environment. Intrathymic DC/M phi could also deliver negative signals. This became apparent when evaluating presentation of TNP in prenatally TNBS-treated mice. Thymus-derived DC/M phi from prenatally TNBS-treated mice could not initiate proliferation of TC in response to TNP-OVA. Instead, when prenatally TNBS-treated mice received an antigenic challenge [TNP-sheep red blood cells (SRBC)], thymic DC/M phi inhibited proliferation of cortisone-resistant TC from untreated and prenatally TNBS-treated mice. This can be explained by assuming that in the process of establishing tolerance, intrathymic DC/M phi may exert cytotoxic/cytostatic activity.

La gestion sanitaire des élevages de rongeurs utilisés en recherche biomédicale: I. La nécessité de disposer d'animaux homogènes dans leur réaction

THE NECESSITY FOR THE DISPOSAL OF HOMOGENEOUS REACTING ANIMALS: This paper points out the principal factors that may influence the course of experimentation using laboratory animals. Particular attention is given to extrinsic factors and to infectious agents.

The molecular biology of coronaviruses

Coronaviruses have recently emerged as an important group of animal and human pathogens that share a distinctive replicative cycle. Some of the unique characteristics in the replication of coronaviruses include generation of a 3' coterminal-nested set of five or six subgenomic mRNAs, each of which appears to direct the synthesis of one protein. Two virus-specific RNA polymerase activities have been identified. Many of the distinctive features of coronavirus infection and coronavirus-induced diseases may result from the properties of the two coronavirus glycoproteins. The intracellular budding site, which may be important in the establishment and maintenance of persistent infections, appears to be due to the restricted intracytoplasmic migration of the E1 glycoprotein, which acts as a matrix-like transmembrane glycoprotein. E1 also exhibits distinctive behavior by self-aggregating on heating at 100°C in sodium dodecyl sulfate (SDS) and by its interaction with RNA in the viral nucleocapsid. The E1 of mouse hepatitis virus (MHV) is an O -linked glycoprotein, unlike most other viral glycoproteins. Thus, the coronavirus system may be a useful model for the study of synthesis, glycosylation, and transport of O -linked cellular glycoproteins.

Analysis of age-dependent resistance to murine coronavirus JHM infection in mice

Resistance to intraperitoneal murine coronavirus JHM infection in mice develops with age. C3H mice were found to be fully susceptible up to the age of 20 days and resistant after 23 days of age. Protection of susceptible animals from death due to infection could be achieved by maternal antibodies or by transfer of spleen cells from immunized, but not from nonimmunized, donor mice. Lack of protection by transfer of unprimed adult spleen cells was not related to immunosuppression by the host. Moreover, resistance of adult mice could not be abrogated by application of lymphocytes from suckling mice, although immune suppression by other means did affect the resistance of adult animals. On the other hand, spleen cells from nonimmunized mice could be primed with inactivated JHM virus in suckling mice and protected these mice from death due to a subsequent virus infection. Thus, the outcome of infection with JHM virus in suckling and adult mice can be influenced by immunological events, but is not exclusively due to the different stages of immune competence.

In vitro macrophage manifestation of cortisone-induced decrease in resistance to mouse hepatitis virus

Genetically resistant G3H mice routinely yielded macrophages that were resistant when grown in 90% horse serum. These mice also routinely yielded macrophages that were susceptible to the same virus, MHV (PRI), in vitro after the mice had been treated with three intraperitoneal doses, of hydrocortisone. Dexamethasone and prednisolone when similarly administered also increased the susceptibility of C3H macrophages taken from the treated animal, but progesterone and testosterone did not. In addition, spleen cells from mice treated with cortisone made the resistant C3H macrophages 100 times more susceptible in vitro. Increased in vitro susceptibility induced in this way by hydrocortisone was reversed by exposure to supernatant fluid removed from cultures of concanavalin A-treated spleen cells.

Role of macrophages in natural resistance to virus infections

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Susceptibility of inbred and outbred mouse strains to Sendai virus and prevalence of infection in laboratory rodents

Sendai virus is one of the more prevalent and serious virus infections of rodents. Infection was found in 66% of the mouse, 63% of the rat, 83% of the hamster, and 44% of the guinea pig colonies examined. Twenty-four inbred and outbred strains of mice were tested for their sensitivity to lethal Sendai virus infection. The 129/J mice tested were approximately 25,000-fold more sensitive than SJL/J mice; however, both mouse strains were similarly permissive in support of viral replication in their lung tissues. Histopathological studies revealed that whereas lesions in both sensitive and resistant mice were qualitatively similar, the lesions in the more sensitive 129/J mice appeared earlier, were much more extensive, and persisted longer than in the resistant SJL/J mice. These results suggest that the observed variance in sensitivity is not the result of a genetic restriction on virus infection and replication but rather is the result of a physiological factor(s) possibly related to some aberration of strain difference in the humoral or cell-mediated immune response.

Genetics of resistance of animals to viruses: I. Introduction and studies in mice

Inherited resistance to animal viruses may be conveniently classified into three types: monogenetic, following simple mendelian ratios; polygenetic; and cytoplasmic. A virus is a unique cellular parasite, dependent upon the host for reproduction and nourishment in a variety of different ways. Since, as with the other types of parasites, the host and the parasite have necessarily evolved together. It is a distortion to consider the resistance of the host, without considering the evolutionary steps in the development of this extreme form of parasitism; therefore, this chapter reviews some of the ideas put forward about host-agent interactions in plants as well as in animals. The importance of genes in regulating the resistance to disease, including parasites and parasitoids, is apparent if the disease is considered to be an important evolutionary force. The selective effects of viruses have not yet been adequately studied. Continued attempts to find a correlation between the different blood groups and differing severity of smallpox infection clearly searched for selective forces, but the results were inconclusive. Most of the knowledge of genetic resistance to virus disease rests on the study of resistance to selected agents in various inbred strains of mice and chickens, rather than on any knowledge of the effects of genetic resistance in a natural heterozygous population. The increasing frequency, however, with which genetic resistance is found, is in itself an evidence that these genes are important in natural outbred populations. In addition, there are increasing numbers of virus diseases, in which the viral agent seems to be inherited in a mendelian fashion.

Macrophages genetically resistant to mouse hepatitis virus converted in vitro to susceptible macrophages

Genetic resistance to mouse hepatitis, which resides largely in the macrophages of resistant C3H mice, may be altered by exposing the cells in vitro to fluid from allogeneic mixed lymphocytes. A 1,000-fold increase in susceptibility was produced in these genetically resistant cells by exposure to this fluid. This presumed lymphokine was effective without producing any change in host adaption of the virus.

Effects of corticosteroid treatment and inflammation on the cellular content of blood and exudate in mice

Inflammatory exudates have been produced in mice by intraperitoneal injection of thioglycollate broth 24 hr and again 3 hr before collecting of the exudate. The first injection of broth exerts a "priming" effect leading to an enhanced response to the second injection. By this procedure more than 30 x 106 leucocytes of which 78 per cent. were polymorphs were obtained from each mouse. Administration of paramethasone reduced the number of cells in the exudate when given at the same time as broth but not when given 3 hr before collection of the exudate. In contrast paramethasone was equally effective when given either 24 hr or 3 hr before harvest in suppressing the appearance of intravenously injected pontamine sky blue in the exudate. It was striking that treatment with paramethasone which had reduced the number of polymorphs in the exudate had actually increased the number in blood.

Experimental visceral aspergillosis

Studies conducted to gain insight into the pathogenesis of experimental aspergillosis indicated that mice pretreated with cortisone acetate and then injected intraperitoneally with nongerminating spores of Aspergillus flavus developed a high incidence of lethal visceral hyphal aspergillosis. A similar, high incidence of fatal infections was observed in cortisone-treated animals in which the number of peritoneal macrophages had been increased by prior injection of thioglycollate. To determine whether germination of spores within the host was important to the subsequent development of disseminated hyphal aspergillosis, germinating spores of A flavus were injected intraperitoneally into normal animals. While a similar dose of nongerminating spores, administered intraperitoneally into normal mice, induced a low incidence of lethal injection, germinating spores induced a high incidence of fatal disease associated with widely disseminated visceral hyphal aspergillosis. Our studies indicate that phagocytic cells in the peritoneal cavity of normal mice are able to ingest nonperminating spores of A flavus and kill them, preventing germination. However, the phagocytic cells are unable to cope with early germinating spores, which then continue to proliferate, leading to extensive hyphal invasion of visceral organs and death.

A comparative immunohistochemical study of splenic arterial hyalinosis in health and disease

Hyaline deposits in arterioles and arteries of spleen were studied immunohistochemically. Hyaline lesions in arteriosclerotic heart disease were characterized by significant deposits of IgG, IgM, beta1C-beta 1A-globulins and beta-lipoproteins. These corresponded to histochemically stained deposits of acid mucopolysaccharides and microscopic areas of musculoelastic tissue damage in the hyaline masses. While, in young adults and a few other cases of other diseases, an occasional granular to linear deposit of IgG, IgM, beta1C-beta 1A-globulin and beta-lipoprotein was noted, no localization of IgA, rabbit antihuman fibrin and rabbit antihuman fibrinogen was seen. A variety of other histochemical staining reactions were found to be negative. These findings suggest that: a) hyaline deposits in splenic arterioles and arteries occur with greater severity in patients with hypertensive and arteriosclerotic heart disease; b) a possible abnormality related to filtration defects in arteries and arterioles, resulting in the trapping of plasma proteins, appears likely; c) increased localization of acid mucopolysaccharides and destruction of musculoelastic tissue is not an uncommon feature in hyaline masses; d) fibrin is not a component of these deposits and e) further study of other organs is necesary to observe the composition of hyaline in arterioles and arteries.

In vitro interaction of mouse hepatitis virus and macrophages from genetically resistant mice. II. Biological characterization of a variant virus MHV (C3H) isolated from stocks of MHV(PRI)

A variant mouse hepatitis virus MHV(C(3)H) to which cultured peritoneal macrophages from both PRI and C(3)H mice were susceptible was isolated from stocks of the MHV(PRI) strain of mouse hepatitis virus. It was cloned on C(3)H macrophage monolayers and killed both adult PRI and C(3)H mice when injected intraperitoneally. This new variant was antigenically indistinguishable from the wild type virus. While the emergence of the variant virus was delayed in the course of infecting C(3)H macrophages with large inocula of MHV(PRI), the second passage grew to a high titer in both cell types without delay. Thus, adaptation to the new host was immediate. Interference, apparently not interferon-mediated, between the two variant viruses may have been the cause for the delay in the emergence of the variant virus. The delayed destruction of C(3)H-cultured macrophages by large inocula of MHV(PRI) uniformly resulted in the emergence of MHV(C(3)H). Whether the new variant emerged as a result of a selection of a pre-existing stable mutant or was conditioned by "growth" in the resistant host was not determined.

Feedback inhibition of the development of macrophage and granulocyte colonies. II. Inhibition by granulocytes

It has been shown that mature normal rat granulocytes produce a substance that inhibits the activity of the inducer required for the development of macrophages (M) and granulocyte (G) colonies from normal hematopoietic cells seeded in soft agar. The granulocyte inhibitor inhibited the activity of the inducer when tested with normal hematopoietic cells from embryonic or adult organs. The inhibitor was not dialyzable, and was obtained in an active form in granulocyte-conditioned medium. The results indicate that the control mechanism that regulates the growth and development of normal macrophages and granulocytes includes a feedback inhibition of the activity of the inducer by inhibitors produced by mature granulocytes and macrophages, presumably at the end of their differentiation process. The inhibition of both M and G colonies by the feedback inhibitors produced by macrophages and granulocytes suggests that both types of colonies may be derived from a common stem cell. A line of primitive myeloid leukemia did not inhibit the activity of the inducer, and the cells of this line were not inhibited by the feedback inhibitors produced by normal granulocytes and macrophages.

Ontogeny of macrophage resistance to mouse hepatitis in vivo and in vitro

Adult or weanling C(3)H mice were found to be genetically resistant to a strain of mouse hepatitis virus. Infant C(3)H mice, however, developed infection and died from mouse hepatitis virus when minimal infectious doses of virus were given to them. There was a delay in the time of death compared to that of the genetically susceptible strain, and the virus recovered from these mice had increased pathogenicity for C(3)H mice. The ontogeny of resistance to hepatitis in the C(3)H mice thus progresses from delayed susceptibility to complete resistance as the age of the host increases. It is reflected in increased resistance of macrophages derived in vitro from liver cultures of infant mice of different ages. This increase in resistance with age was reduced by maintaining the cultures for a longer period of time before inoculation, or by increasing the number of explants in a given culture. Resistant cells were uniformly furnished by mice age 16 days, or more. It is concluded that a process of maturation of resistance of the cells takes place after the mice are born, but that this does not continue under in vitro conditions, and that it may be modified by the environment of the cells.

The role of macrophages in the induction of antibody in x-irradiated animals

A study was carried out on the function of macrophages in inducing antibody production to Shigella antigen, and on the effect of X-irradiation on the `immunogenic' function of macrophages. Peritoneal macrophages, which had been incubated with Shigella and then injected into mice exposed to 550 r, triggered the formation of agglutinating antibody in animals which did not respond to the injection of the antigen alone. The antibody formed was not produced by `contaminating' lymphocytes of the peritoneal exudate, since: (a) lymph node cells at doses higher than those of the macrophage inocula did not produce antibody when treated and injected under similar conditions, and (b) lymphocyte-free macrophage populations, obtained by culturing in vitro cells of peritoneal exudates, triggered the production of antibody when injected in to X-irradiated recipients after interaction with the antigen. Macrophages from irradiated donors incubated with Shigella were incapable of inducing antibody formation in X-irradiated mice. Animals exposed to higher doses of irradiation (900 r) did not produce antibody following injection of macrophage—antigen complexes. It was, therefore, concluded that macrophages from normal animals elicited the production of antibody by the lymphoid cells of the irradiated recipients.

In vitro control of the development of macrophage and granulocyte colonies

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