Characterization and cytotoxic activity of sulfated derivatives of polysaccharides from Agaricus brasiliensis

Agaricus brasiliensis cell-wall polysaccharides isolated from fruiting body (FR) and mycelium (MI) and their respective sulfated derivatives (FR-S and MI-S) were chemically characterized using elemental analysis, TLC, FT-IR, NMR, HPLC, and thermal analysis. Cytotoxic activity was evaluated against A549 tumor cells by MTT and sulforhodamine assays. The average molecular weight (Mw) of FR and MI was estimated to be 609 and 310 kDa, respectively. FR-S (127 kDa) and MI-S (86 kDa) had lower Mw, probably due to hydrolysis occurring during the sulfation reaction. FR-S and MI-S presented ~14% sulfur content in elemental analysis. Sulfation of samples was characterized by the appearance of two new absorption bands at 1253 and 810 cm(-1) in the infrared spectra, related to S=O and C-S-O sulfate groups, respectively. Through (1)H and (13)C NMR analysis FR-S was characterized as a (1→6)-(1→3)-β-D-glucan fully sulfated at C-4 and C-6 terminal and partially sulfated at C-6 of (1→3)-β-D-glucan moiety. MI-S was shown to be a (1→3)-β-D-gluco-(1→2)-β-D-mannan, partially sulfated at C-2, C-3, C-4, and C-6, and fully sulfated at C-6 of the terminal residues. The combination of high degree of sulfation and low molecular weight was correlated with the increased cytotoxic activity (48 h of treatment) of both FR-S (EC₅₀=605.6 μg/mL) and MI-S (EC₅₀=342.1 μg/mL) compared to the non-sulfated polysaccharides FR and MI (EC₅₀>1500 μg/mL).

Inhibition of Vaccinia virus entry by a broad spectrum antiviral peptide

Concerns about the possible use of Variola virus, the causative agent of smallpox, as a weapon for bioterrorism have led to renewed efforts to identify new antivirals against orthopoxviruses. We identified a peptide, EB, which inhibited infection by Vaccinia virus with an EC(50) of 15 microM. A control peptide, EBX, identical in composition to EB but differing in sequence, was inactive (EC50>200 microM), indicating sequence specificity. The inhibition was reversed upon removal of the peptide, and EB treatment had no effect on the physical integrity of virus particles as determined by electron microscopy. Viral adsorption was unaffected by the presence of EB, and the addition of EB post-entry had no effect on viral titers or on early gene expression. The addition of EB post-adsorption resulted in the inhibition of beta-galactosidase expression from an early viral promoter with an EC(50) of 45 microM. A significant reduction in virus entry was detected in the presence of the peptide when the number of viral cores released into the cytoplasm was quantified. Electron microscopy indicated that 88% of the virions remained on the surface of cells in the presence of EB, compared to 37% in the control (p<0.001). EB also blocked fusion-from-within, suggesting that virus infection is inhibited at the fusion step. Analysis of EB derivatives suggested that peptide length may be important for the activity of EB. The EB peptide is, to our knowledge, the first known small molecule inhibitor of Vaccinia virus entry.

Low dose latrunculin-A inhibits dexamethasone-induced changes in the actin cytoskeleton and alters extracellular matrix protein expression in cultured human trabecular meshwork cells

We determined the effects of a low dose of the actin-disrupting agent latrunculin (LAT)-A on dexamethasone (DEX)-induced changes in actin organization, focal adhesions, and production of extracellular matrix proteins in cultured human trabecular meshwork (HTM) cells. HTM cells were cultured to a highly confluent stage with stable endothelium-like morphology and incubated with 0.1 or 0.2 microM DEX and/or 0.1 microM LAT-A. Changes in the actin cytoskeleton and vinculin-containing focal contacts were evaluated by immunofluorescence microscopy. Expression of thrombospondin-1 (TSP1) and fibronectin (FN) in HTM cells was evaluated by Western blot analysis. The results showed that DEX induced morphological changes and actin reorganization in HTM cells. The cells partly recovered after DEX withdrawal, but the addition of low dose LAT-A hastened the recovery. In addition, DEX failed to induce changes when co-incubated with LAT-A for at least 4 weeks, and for at least 2 weeks when cells were pre-treated with LAT-A for 2 weeks. HTM cells treated with 0.1 microM LAT-A only for 5 days showed mild disorganization of the actin cytoskeleton and focal adhesions, which persisted during the 4 weeks of treatment. DEX stimulated production of FN in HTM cells independent of LAT-A treatment. LAT-A and, to a lesser extent, DEX inhibited production of TSP1 by HTM cells. Although LAT-A is not a DEX receptor antagonist, it is able to prevent the effects of DEX on the actin cytoskeleton in cultured HTM cells at a dose subthreshold for increasing outflow facility in monkeys. This suggests that LAT-A at low doses may be useful in treating steroid and other glaucomas. TSP1 may be an important target of LAT-A in HTM cells and modulation of TSP may influence the actin cytoskeleton of the trabecular meshwork (TM), and consequently, intraocular pressure.

Mutation of the herpes simplex virus 1 KOS UL45 gene reveals dose dependent effects on central nervous system growth

The herpes simplex virus type 1 (HSV-1) UL45 gene encodes an 18 kDa virion envelope protein whose function remains unknown. Previous studies using a UL45 null mutant, UL45A, demonstrated that deletion of the UL45 gene altered plaque size in Vero and HeLa cells, but was not essential for replication in these cell types. The goal of this study was to determine if mutation of the UL45 gene influenced virus growth in the CNS. Two UL45 mutants, as well as a repaired revertant virus, were constructed and tested for their ability to cause encephalitis and replicate in the CNS. The UL45 mutants were not lethal when 1 x 10(3) pfu were injected intracerebrally into Balb/c mice. In contrast, at inocula greater than 1 x 10(3), the UL45 mutants were lethal. In vivo growth curves derived from mice inoculated intracerebrally with 1 x 10(3) pfu of virus revealed that the mutants grew poorly compared to wild type or revertant viruses. These results suggest that the 18 kDa UL45 gene product is required for efficient growth in the central nervous system at low doses. We propose that the UL45 gene may play an important role under the conditions of a naturally acquired infection.

Effect of H-7 on cultured human trabecular meshwork cells

PURPOSE

To determine the effect of the serine-threonine kinase inhibitor H-7, which blocks actomyosin contractility and increases outflow facility in live monkeys, on morphology, cytoskeleton, and cellular adhesions of human trabecular meshwork (HTM) cells in culture.

METHODS

Cultured HTM cells were videographically recorded and evaluated before and after exposure to H-7 at different concentrations. The subcellular distribution of the actin-based cytoskeleton and associated anchor proteins including vinculin, paxillin, and beta-catenin, as well as phosphotyrosine-containing proteins were evaluated by fluorescence immunocytochemistry and digital fluorescence microscopy.

RESULTS

H-7 induced pronounced but reversible HTM cell thickening toward the cell center and deterioration of the actin cytoskeletal network. Cell-extracellular matrix (ECM) and cell-cell adhesions were also affected, but the beta-catenin-rich, vinculin-containing adherens junctions were clearly more resistant than focal contacts. Phosphotyrosine labeling in focal contacts was highly sensitive to H-7.

CONCLUSIONS

H-7 induces alterations in cell shape, actin cytoskeleton, and associated focal adhesions in cultured HTM cells, which may be responsible for the effects of H-7 on outflow facility in live monkey eyes.

HSV-1 Vector-Delivered FGF2 to the Retina Is Neuroprotective but Does Not Preserve Functional Responses

Fibroblast growth factor 2 (bFGF, FGF2) exhibits mitogenic, angiogenic, wound healing, and neuroprotective properties. Infusion of FGF2 in vivo to treat neurodegenerative disorders in animal models results in increased survival of damaged neurons, but these effects are transient. To test the feasibility of HSV vector-delivered FGF2 for neuroprotection, we inserted the FGF2 gene under the control of the HCMV immediate-early promoter into an attenuated avirulent HSV-1 vector. Transduction with FGF2/HSV-1 virus promoted survival of PC12 cells, induced differentiation of these cells to the neuronal phenotype in vitro, and protected PC12 neuronal cells from death induced by nerve growth factor withdrawal. The attenuated FGF2/HSV-1 virus was able to deliver and direct expression of the FGF2 gene in the eye. Delivery prior to light exposure in a rat model of retinal degeneration resulted in significant protection against photoreceptor loss. However, functional ERG responses were not detected. Treatment of normal eyes with the vector alone suppressed ERGs, which were only partially restored in eyes receiving the FGF2 vector. Thus, although the FGF2-HSV-1 virus induced preservation of cell and tissue structure, this was not sufficient to protect photoreceptor function.

Modified FGF4 signal peptide inhibits entry of herpes simplex virus type 1

Entry of herpes simplex virus type 1 (HSV-1) into host cells occurs through fusion of the viral envelope with the plasma membrane and involves complex and poorly understood interactions between several viral and cellular proteins. One strategy for dissecting the function of this fusion machine is through the use of specific inhibitors. We identified a peptide with antiviral activity that blocks HSV-1 infection at the entry stage and during cell-to-cell spreading. This peptide (called EB for "entry blocker") consists of the FGF4 signal sequence with an RRKK tetramer at the amino terminus to improve solubility. The activity of EB depends exclusively but not canonically on the signal sequence. Inhibition of virus entry (hrR3) and plaque formation (KOS) strongly depend on virus concentrations and serum addition, with 50% inhibitory concentrations typically ranging from 1 to 10 microM. Blocking preadsorbed virus requires higher EB concentrations. Cytotoxic effects (trypan blue exclusion) are first noted at 50 microM EB in serum-free medium and at > or = 200 microM in the presence of serum. EB does not affect gC-dependent mechanisms of virus attachment and does not block virus attachment at 4 degrees C. Instead, EB directly interacts with virions and inactivates them irreversibly without, however, disrupting their physical integrity as judged by electron microscopy. At subvirucidal concentrations, EB changes the adhesive properties of virions, causing aggregation at high virus concentrations. This peptide may be a useful tool for studying viral entry mechanisms.

Herpes simplex virus-mediated gene delivery to the rodent visual system

PURPOSE

To determine the types of cells in the visual system of the mouse and rat that can express a transgene delivered by an attenuated replication competent Herpes simplex virus-1 (HSV-1) vector.

METHODS

C57/BL6 x BALB/C mice and Albino rats were treated with 1 x 10(7) pfu of the HSV-1 ribonucleotide reductase mutant (hrR3) expressing the Escherichia coli lacZ gene. The hrR3 virus was delivered by topical application to the cornea, intravitreal (IV) injection, intracameral injection (IC), or stereotactic injection into the visual cortex (VC). At specified times postinfection, animals were killed and tissues were removed, fixed, sectioned, and stained with X-gal or hematoxylin and eosin for histochemical and histopathologic examination.

RESULTS

Topical delivery after corneal scarification in both mouse and rat resulted in lacZ expression in 25% of the corneal epithelial cells and 25% of the retinal pigment epithelium (RPE) cells. Topical application without concurrent scarification also resulted in transgene delivery to 20% of the RPE cells of the rat but not the mouse. IV injection resulted in expression primarily in RPE cells, with up to 100% of the cells expressing lacZ in the mouse and rat. Other cells expressing the transgene included ciliary body (CB) and optic nerve cells. Up to 25% of the retinal ganglion cells in the rat expressed lacZ, but only rarely in mice. IC delivery in rats resulted in expression in trabecular meshwork, CB cells, RPE, and iris epithelium. Injection into area 17 of the rat VC resulted in efficient labeling of the VC neurons and neurons in the lateral geniculate nucleus without any evident pathology or inflammation. Neither inflammation nor disease pathology was observed in either the mouse or rat after any route of delivery.

CONCLUSIONS

It was demonstrated that the hrR3 HSV-1 virus can deliver a functioning gene to several cell types in the eye and neurons in the VC and that the virus can move via retrograde transport to nuclei that project to the VC.

Herpes simplex virus mediated gene transfer to primate ocular tissues

We evaluated the feasibility of delivering a gene into monkey eyes using a replication-competent herpes simplex virus (HSV) type 1 ribonucleotide reductase mutant (hrR3) expressing the Escherichia coli lacZ gene. To determine the efficiency of in vitro HSV-mediated gene transfer, cultured human trabecular meshwork (HTM) and human ciliary muscle (HCM) cells were infected with hrR3 and beta-galactosidase activity was measured histochemically. Six cynomolgus monkey eyes received viral injections into the anterior chamber (2 x 10(7) pfu) and/or the vitreous (5 x 10(7) pfu), and the distribution of cells expressing lacZ was evaluated. In vitro, both cultured HTM and HCM cells displayed multiplicity-dependent beta-galactosidase activity. In vivo, intracameral and/or intravitreal injection resulted in transgene expression in TM cells and in non-pigmented ciliary epithelial cells (NPE), but not in CM cells. Transgene expression was also detected in retinal pigmented epithelial (RPE) cells and sporadic retinal ganglion cells (RGC) in eyes receiving virus intracamerally and intravitreally respectively. We observed significant inflammation in the anterior chamber, TM and CM in virus-injected eyes, along with mild vitritis and retinitis. This study demonstrates successful gene transfer using hrR3 as a vector in human ocular cells and in ocular tissues in living monkeys. Further investigation of the etiology of the inflammatory response, possible cytotoxicity, and limited duration of transgene expression is necessary in order to make this technique clinically applicable.

Isolation and partial characterization of an antiviral, RC-183, from the edible mushroom Rozites caperata

A protein of 10,425 Da was purified from the edible mushroom Rozites caperata and shown to inhibit herpes simplex virus types 1 and 2 replication with an IC50 value of < or = 5 microM. The protein designated RC-183 also significantly reduced the severity of HSV-1 induced ocular disease in a murine model of keratitis, indicating in vivo efficacy. HSV mutants lacking ribonucleotide reductase and thymidine kinase were also inhibited, suggesting the mechanism does not involve these viral enzymes. Antiviral activity was also seen against varicella zoster virus, influenza A virus, and respiratory syncytial virus, but not against adenovirus type VI, coxsackie viruses A9 and B5, or human immunodeficiency virus. Characterization of RC-183 by mass spectroscopy, sequencing, and other methods suggests it is composed of a peptide (12 or 13 mer) coupled to ubiquitin via an isopeptide bond between the c-terminal glycine of ubiquitin and the epsilon amino group of a lysine residue in the peptide. The peptide sequence did not match any known sequence. Thus, RC-183 is a novel antiviral that may have clinical utility or serve as a lead compound for further development. Determining the mechanism of action may lead to identification of novel steps in viral replication.

1,25-Dihydroxyvitamin D3 prolongs graft survival without compromising host resistance to infection or bone mineral density

BACKGROUND

Recently, we have shown that 1,25-dihydroxyvitamin D3 prolongs graft survival in mice and rats when the donor and recipient differ at two or more major histocompatability loci. Among the most serious side effects encountered with the currently available transplantation antirejection drugs are an increased susceptibility to infection and decreased bone mineralization. Our results suggest that 1,25-dihydroxyvitamin D3 prolongs graft survival without these side effects of bone loss and susceptibility to infection.

METHODS

We compared the ability of 1,25-dihydroxyvitamin D3-treated, nontreated, or cyclosporine (CsA)-treated mice to resist infection with Candida albicans and herpes simplex virus-1. To determine bone density, femurs were collected from nontreated, 1,25-dihydroxyvitamin D3-treated (50 ng/mouse/day), or CsA-treated (25 mg/kg/day) mice, and bone ash was determined.

RESULTS

Here we show that 1,25-dihydroxyvitamin D3 treatment does not increase the susceptibility of the host to fungal or viral infection. Furthermore, CsA causes bone loss, whereas 1,25-dihydroxyvitamin D3 actually increases bone mass.

CONCLUSIONS

The use of 1,25-dihydroxyvitamin D3 and its analogs to increase transplant survival will avoid bone loss and opportunistic infection, two important disadvantages of the most widely used transplant antirejection drugs--CsA and the glucocorticoids.

Treatment of spontaneously arising retinoblastoma tumors in transgenic mice with an attenuated herpes simplex virus mutant

The use of viruses to treat tumors has received renewed interest with the availability of genetically defined attenuated mutants. Herpes simplex virus (HSV) type 1 in particular has been shown to be effective for tumors of neuronal origin. However, the model systems used for these studies rely on the use of explanted tumor cells in immunodeficient animals. We have used a recently developed transgenic mouse model, wherein mice spontaneously develop retinoblastomas, to determine if a mutant HSV has a therapeutic effect against an endogenously arising tumor in an immunocompetent host. The injection of 1 x 10(6) PFU of the neuroattenuated HSV-1/HSV-2 recombinant RE6 into the vitreous of transgenic mice resulted in a significant inhibition of tumor growth compared to injection of medium alone (P = 0.0063). Immunohistochemical analysis of viral antigen showed that viral replication was restricted to focal areas of the tumors and the retinal pigment epithelium. Viral growth was not significantly different in the eyes of transgene-positive and transgene-negative mice, suggesting that enhanced replication in tumor cells may not explain the effects. Tumor cells in the treated eyes were significantly less differentiated than those in the untreated eyes (P = 0.04), suggesting that the virus may replicate better in certain cell types in the tumors. Although the injection of RE6 resulted in a difference in tumor size, the treatment did not result in the elimination of tumors in any of the mice improvements in the efficacy of tumor control are needed if this therapy is to be of use.

The herpes simplex virus type 1 ribonucleotide reductase is required for acute retinal disease

We have used a herpes simplex virus type 1 (HSV-1) ribonucleotide reductase (RR) null mutant (ICP6 delta) to determine if the HSV-1 RR is required for acute retinal disease. Injection of the ICP6 delta mutant into the vitreous induced mild transient signs of infection (vitreal infiltrate, retinal inflammation, and changes in retinal cytology). In contrast, the parental KOS and a revertant virus (ICP6 delta + 3.1) in which the RR gene had been restored, caused severe retinitis. Injection of media alone also induced mild transient signs of disease. Two months after infection, ICP6 delta injected eyes could not be distinguished from normal eyes. Repeated injection of ICP6 delta (3 times, 2 weeks apart) resulted in vitreal infiltrate near the site of injection but the retina did not appear damaged. The mutant, ICP6 delta, grew to peak titers 1 x 10(3) to 1 x 10(5)-fold lower and cleared faster than KOS or ICP6 delta + 3.1 in the injected eyes suggesting that the reduced virulence was due to reduced ability of the virus to grow. These results show that the viral RR is required for acute retinal disease.

Maturation of collagen fibrils in the corneal stroma results in masking of tyrosine-rich region of type V procollagen

PURPOSE

To determine the molecular form of type V procollagen in collagen fibrils in mammalian corneal stromas.

METHODS

The presence of the tyrosine-rich region in the NH2-propeptide of type V procollagen in collagen fibrils was examined in human, bovine, and mouse corneas and human corneal fibroblast cultures by immunofluorescence microscopy and immunoblot analysis using a polyclonal antibody specific for this region. The antibody was generated using a glutathione S-transferase-fusion peptide.

RESULTS

The tyrosine-rich region was detected readily in frozen sections of 5- to 6-month-old mouse corneal stromas without the need for any unmasking techniques, indicating that this domain is exposed on the surface of striated collagen fibrils. In contrast, frozen sections of adult human and bovine corneas did not label with the polyclonal sera to the tyrosine-rich region. Immunoblot analysis of bacterial collagenase digests of human and bovine corneas, however, indicated that peptide fragments containing the tyrosine-rich region of type V procollagen and of the expected molecular weight of 70 to 85 kDa were present. Further immunofluorescence microscopic studies and immunoblot analysis of mouse corneas at different ages and of collagen fibrils formed in human corneal fibroblast cultures over time indicated that, initially, the tyrosine-rich region of type V procollagen could be detected in all these collagen fibrils; however, as the age of the mouse and the culture increased, the ability to detect this region decreased.

CONCLUSIONS

These results suggest that, in vivo, the tyrosine-rich region of type V procollagen is retained on type V procollagen molecules within mammalian collagen fibrils from corneal stromas and that this region becomes masked as collagen fibrils mature or the species ages.

Evaluation of a peptidomimetic ribonucleotide reductase inhibitor with a murine model of herpes simplex virus type 1 ocular disease

The ribonucleotide reductase (RR) of herpes simplex virus type 1 (HSV-1) is an important virulence factor, being required for neurovirulence, ocular virulence, and reactivation from latency. The RR activity requires the association of two distinct homodimeric subunits, and the association of the subunits is inhibited in the presence of a peptide homologous to the carboxy terminus of the small subunit. A structural analog of the inhibitory peptide (BILD 1263) has been shown to inhibit the replication of HSV-1 at micromolar concentrations in vitro. We used a mouse model of HSV-1 ocular infection to determine the in vivo efficacy of topical BILD 1263. Treatment of HSV-1 KOS-infected mice resulted in significant reductions in the severity and incidence of stromal keratitis and corneal neovascularization. At higher concentrations (5%) BILD 1263 reduced the severity but not the incidence of blepharitis. Treatment with 5% BILD 1263 also reduced viral shedding from the cornea by 10- to 14-fold (P < 0.001). In uninfected mice treated with 5% BILD 1263, we found no evidence of corneal epithelial damage, conjunctivitis, or blepharitis, and histopathological studies revealed no changes in the corneas of these mice. These results show that the peptidomimetic RR inhibitor BILD 1263 is effective in preventing disease, has an antiviral effect in vivo, and has little or no toxicity.

Thymidine kinase and susceptibility to interferon are not involved in the increased virulence of recombinant viruses isolated following mixed ocular infection with HSV strains OD4 and CJ394

We previously described the isolation of herpes simplex virus type 1 (HSV-1) intratypic recombinants that had increased ocular and neurovirulence. To better understand the mechanism of increased virulence, we have characterized two virulence-related factors, viral thymidine kinase (TK) activity and interferon (IFN) sensitivity, in the parental and recombinant viruses. The parental and recombinant viruses had comparable TK activities and were equally resistant to IFN-alpha, IFN-gamma and to a combination of the two IFNs. These results indicate that these factors are not involved in the increased virulence of the recombinant viruses.

Evidence for an interaction of herpes simplex virus with chondroitin sulfate proteoglycans during infection

In a previous study, a mouse L cell mutant was isolated which is 90% resistant to HSV-1 infection (S. Gruenheid, L. Gatzke, H. Meadows, and F. Tufaro. J. Virol. 67, 93-100, 1993). This cell line, termed gro2C, failed to express heparan sulfate (HS)-glycosaminoglycans on the cell surface, which normally act as initial receptors for HSV-1 attachment to cultured cells. In this report, we extended the characterization of gro2C cells to explore the possibility that cell-surface chondroitin sulfate (CS) facilitates virus attachment to gro2C cells in the absence of HS. We found that soluble CS types A, B, and C strongly interfere with adsorption of HSV-1 to the surface of gro2C cells in a dose-dependent manner, and CS type B (dermatan sulfate) inhibited adsorption to parental (control) L cells by up to 10%. Moreover, gro2C cell infection was hypersensitive to inhibition by HS in comparison to control L cell infection. In all cases, a decrease in adsorption resulted in a decrease in infection. By contrast, the highly-sulfated glycosaminoglycan analog dextran sulfate was a relatively poor inhibitor of gro2C cell infection, indicating that the inhibitory effects of CS were related to its carbohydrate structure and not solely to its strong negative charge. By using a mutant virus strain which does not express the heparin-binding glycoprotein gC, we show that gC was not required for infection of gro2C cells, and was not required for the inhibition by HS or CS. Thus, the characterization of gro2C cell infection has revealed that one or more components of the HSV-1 particle can interact with cell-surface CS as well as HS to mediate infection of susceptible cells.

The effect of viral inoculum level and host age on disease incidence, disease severity, and mortality in a murine model of ocular HSV-1 infection

It has been previously shown that the strain of virus, immune competence of the host, and innate resistance of the host have an effect on the severity of ocular disease induced by topical infection with herpes simplex virus type 1 (HSV-1). This study has expanded on earlier work by examining the effect of virus inoculum and host age on mortality, incidence of ocular disease, and severity of ocular disease. BALB/c mice were infected with inocula ranging from 2 x 10(3) to 1 x 10(6) pfu of HSV-1 strain CJ394. The most significant effect of variation in the inoculum was on the percent of mice developing disease. Increasing the inoculum resulted in significantly increased disease incidence, but at 5 x 10(3) pfu/mouse or higher, there was little difference in disease severity in those animals exhibiting symptoms. Decreasing host age also resulted in a significant increase in the incidence of ocular disease, but the dependence of disease severity on host age varied with the symptom being scored. In animals exhibiting disease, the peak severity of stromal keratitis and vascularization of the cornea were unaffected by host age. However, the severity of blepharitis was significantly reduced in older mice. Increasing host age also resulted in increased resistance to encephalitis. Three to four-week old mice were very susceptible to encephalitis (100% mortality), while only 20% of 4-5 week old mice died by day 15 post-infection. Mice older than 5 weeks were completely resistant to lethal encephalitis after corneal infection.

Recombinants are isolated at high frequency following in vivo mixed ocular infection with two avirulent herpes simplex virus type 1 strains

Mixed infections with different strains of herpes simplex virus type 1 (HSV-1) may result in more severe disease than infection with either strain alone. This phenomenon is important because it may facilitate the identification of virulence genes through the transfer of virulence determinants between complementing strains, and it may pose a problem in the use of attenuated HSV strains for vaccines and gene delivery vectors. In this study, we have compared the percentage of recombinants present after mixed infection with HSV-1 strains OD4 and 994 in vitro and in vivo. After corneal inoculation, we found that 74% of randomly picked isolates from the trigeminal ganglia were recombinants, compared with 59% from the cornea. Twenty-six percent of randomly picked isolates were recombinant following mixed infection of Vero cells in vitro. Seventeen recombinant strains isolated from the in vivo mixed infections were assayed for ocular virulence, and they were found to exhibit a wide range of virulence phenotypes. The presence of virulent recombinants suggests that recombination plays a role in the increased disease observed in this mixed infection, and the broad range of virulence indicates that there may be multiple genetic factors involved in the increased virulence observed after mixed infection with these two strains. The recombinants were also tested for their ability to grow in NIH 3T3 fibroblasts, and though some correlation was observed between growth in vitro and ability to cause ocular disease, improved growth in murine cells does not sufficiently explain the increased virulence observed in some recombinants.

IFN-alpha induces MxA gene expression in cultured human corneal fibroblasts

Treatment of certain human cells with Interferon-alpha (IFN-alpha) induces the synthesis of a 76 kDa protein designated MxA that is involved in resistance to viral infection. We have used a specific cDNA clone and monoclonal Ab to show that MxA is induced in IFN-alpha treated human corneal fibroblast cultures. Mx RNA was increased 23-fold and 45-fold after 5 and 9 h of IFN-alpha treatment, respectively. The MxA protein was detectable by immunoblotting at 5 hr after IFN treatment and peaked at 17 hr. Concentrations of IFN-alpha as low as 1 U/ml induced detectable amounts of MxA, and expression was maximal at 1 x 10(3) U ml-1. These results confirm that MxA synthesis is induced in human corneal fibroblasts treated with IFN-alpha.

Renin mRNA is synthesized locally in rat ocular tissues

Components of the Renin Angiotensin System (RAS) have been detected in ocular tissues and fluids. The source of the ocular RAS proteins is unknown but possibilities include diffusion or leakage from the systemic circulation, specific uptake from the blood, or local synthesis. We have used RT-PCR and in situ hybridization (ISH) to show that renin mRNA is present in ocular tissues from 3 strains of rats. By RT-PCR, we found 10 of 15 ciliary body samples, 13 of 16 iris samples, and 1 of 3 retina samples were positive for renin mRNA. Also, 6 of 6 brain and 7 of 8 kidney samples were positive. Using ISH, we found renin mRNA in the ciliary muscle adjacent to the sclera extending into the choroid. Tissue near the outflow channels of the anterior chamber angle also labeled. Retinal labeling was weak but present in the nerve fiber layer. Clusters of grains, possibly representing blood vessels, were also seen in the ciliary body, iris, and retina using ISH. These results suggest the presence of a local ocular RAS.

Rapid small-scale isolation of herpes simplex virus DNA

A method has been developed for the rapid isolation of herpes simplex virus DNA analogous to miniprep methods for bacterial plasmid isolation. Infected Vero cells are lysed with three freeze-thaw cycles, and the nuclei are removed by centrifugation. DNA is released from the virions in the supernatant by proteinase K digestion. Then the DNA is extracted with phenol/chloroform and precipitated with ethanol. This method requires only small amounts of infected cells as a source of viral DNA, does not use radioactivity, and routinely produces DNA of sufficient purity to be used for restriction fragment length polymorphism (RFLP) analysis on ethidium-stained gels.

Glycoprotein C-independent binding of herpes simplex virus to cells requires cell surface heparan sulphate and glycoprotein B

Previous studies have shown that the initial interaction of herpes simplex virus (HSV) with cells is binding to heparan sulphate and that HSV-1 glycoprotein C (gC) is principally responsible for this binding. Although gC-negative viral mutants are impaired for binding and entry, they retain significant infectivity. The purpose of the studies reported here was to explore the requirements for infectivity of gC-negative HSV-1 mutants. We found that absence or alteration of cell surface heparan sulphate significantly reduced the binding of gC-negative mutant virus and rendered cells resistant to infection, as shown previously for the wild-type virus. We isolated a recombinant double-mutated HSV strain that produces virions devoid of both of the known heparin-binding glycoproteins, gB and gC. The drastically impaired binding of these mutant virions to cells, relative to gC-negative and wild-type virions, indicates that gB mediates the binding of gC-negative virions to cells. Thus at least two HSV glycoproteins can independently mediate the binding of HSV to cell surface heparan sulphate to start the process of viral entry into cells.

Interferon-alpha and interferon-gamma induced modulation of proteins in human corneal fibroblasts

Little is known about the effects of interferon (IFN) on cell function in the eye. We have analyzed the effect of INF-alpha and IFN-gamma on the expression of proteins in cultured human corneal fibroblasts. Treatment with IFN-alpha increased the synthesis of proteins of 84, 76, 52, and 28 kD and decreased the synthesis of a 72-kD protein. Treatment with IFN-gamma increased the synthesis of proteins of 83, 66, 64, 54, and 47 kD. The effect of IFN-alpha and IFN-gamma were first detected at 5-9 h and 9 h, respectively, after the addition of the IFNs and were maximal at 17 and 24 h, respectively. Most of the changes were seen at doses of 1 x 10(1) to 1 x 10(2) U/ml of IFN-alpha or IFN-gamma and were maximal at 1 x 10(2) to 1 x 10(3) U/ml. Thus, each IFN induced distinct proteins based on apparent molecular weight and isoelectric point. These results show that IFN-alpha and IFN-gamma affect the synthesis of small groups of distinct proteins in human corneal fibroblasts.

The HSV-1 UL45 18 kDa gene product is a true late protein and a component of the virion

Previously we constructed a null mutation in the HSV-1 UL45 gene, showed that the UL45 gene was not required for growth in Vero cells, and confirmed that it coded for an 18 kDa protein (R.J. Visalli and C.R. Brandt, Virology 185:419-423, 1991). In this study, we have continued our characterization of the UL45 gene and the 18 kDa protein. Analysis of UL45 RNA revealed that the gene was expressed late and was inhibited in the presence of phosphonoacetic acid (paa), indicating it is a gamma 2 class gene. Using a specific polyclonal antiserum, we found that the 18 kDa UL45 gene product was also expressed late and was inhibited in the presence of paa. The 18 kDa protein was present in purified virions and was substantially enriched in the envelope-tegument fraction of virions disrupted with NP-40 detergent. The 18 kDa protein is thus a structural protein of the virus and appears to be associated with the viral envelope. A 20 kDa protein that cross-reacted with a polyclonal HSV-1 UL45 antiserum was also detected in cells infected with HSV-2 strain 333.

IFN-gamma-mediated antimicrobial response. Indoleamine 2,3-dioxygenase-deficient mutant host cells no longer inhibit intracellular Chlamydia spp. or Toxoplasma growth

The role of indoleamine 2,3-dioxygenase (IDO) in IFN-gamma-mediated inhibition of intracellular parasite growth has been examined previously, although earlier work has been largely correlative. In this study, we defined more completely the role of IDO in the IFN-antimicrobial response. Two mutant cell lines, derived from ME180 cells and exhibiting reduced IDO activity (IR3B6A, IR3B6B) were characterized to determine if they retained the capacity to inhibit intracellular Chlamydia and Toxoplasma growth. Mutant cells treated with IFN-gamma exhibited reduced capacity to suppress pathogen growth. The expression of several IFN-regulated genes also was measured to confirm that the inability to inhibit pathogen growth was because of the lack of IDO. The expression of class II MHC, intracellular adhesion molecule-1, MxA, and P68 kinase genes was induced in the IFN-gamma-treated wild type ME180 cells, but was variable in the mutant cell lines, supporting the hypothesis that IFN-gamma-induced production of IDO is a key IFN-gamma-mediated antimicrobial mechanism.

IFN-gamma-mediated antimicrobial response. Indoleamine 2,3-dioxygenase-deficient mutant host cells no longer inhibit intracellular Chlamydia spp. or Toxoplasma growth

The role of indoleamine 2,3-dioxygenase (IDO) in IFN-gamma-mediated inhibition of intracellular parasite growth has been examined previously, although earlier work has been largely correlative. In this study, we defined more completely the role of IDO in the IFN-antimicrobial response. Two mutant cell lines, derived from ME180 cells and exhibiting reduced IDO activity (IR3B6A, IR3B6B) were characterized to determine if they retained the capacity to inhibit intracellular Chlamydia and Toxoplasma growth. Mutant cells treated with IFN-gamma exhibited reduced capacity to suppress pathogen growth. The expression of several IFN-regulated genes also was measured to confirm that the inability to inhibit pathogen growth was because of the lack of IDO. The expression of class II MHC, intracellular adhesion molecule-1, MxA, and P68 kinase genes was induced in the IFN-gamma-treated wild type ME180 cells, but was variable in the mutant cell lines, supporting the hypothesis that IFN-gamma-induced production of IDO is a key IFN-gamma-mediated antimicrobial mechanism.

Heterogeneity of type I collagen expression in human corneal keratoconus fibroblasts

Corneal fibroblast cultures were established from 3 normal and 4 keratoconus (KC) corneas. Type I collagen protein synthesis and steady-state RNAs were analyzed in these cultures by metabolic labeling studies, slot blots and immunofluorescent microscopy. Type I collagen proteins and steady-state RNAs were reduced in cells from 3 of the 4 KC cultures when compared with normal fibroblasts, suggesting that collagen expression is heterogenous in KC and that the heterogeneity is expressed at the cellular and molecular level. The type I collagen matrix synthesized by the KC fibroblasts appeared normal when analyzed by immunofluorescence, suggesting that the incorporation of type I collagen into the extracellular matrix is not affected in KC fibroblasts.

Enhanced inhibition of herpes simplex virus type 1 growth in human corneal fibroblasts by combinations of interferon-alpha and -gamma

Trials testing the topical treatment of herpes simplex virus (HSV) ocular infections with single interferons (IFN) have provided mixed results. To determine if combination therapy with IFN may be more effective, the ability of combinations of IFN-alpha and IFN-gamma to inhibit HSV growth in human corneal fibroblasts (HCF) was assessed. Virus yields were reduced 282-fold and 37-fold, respectively, in HCF treated with either IFN-alpha or IFN-gamma (10(3) units/mL each). In cells treated with a combination of IFN-alpha and IFN-gamma (10(3) units/mL each), an average reduction of 5.1 x 10(5)-fold in the yield of infectious virus was achieved. Combinations of IFN-alpha and IFN-gamma considerably enhanced the antiviral effect in HCF, suggesting that combination treatment may be efficacious against ocular HSV infections; these findings provide a possible explanation at the cellular level for the poor results achieved in previous clinical trials.

An ocular renin-angiotensin system. Immunohistochemistry of angiotensinogen

The circulating renin-angiotensin system (RAS) is an important determinant in maintaining adequate systemic blood pressure, and it also may modify organ-specific blood flow. All recognized RAS components have been identified in the eye. In this study, angiotensinogen (ANG) was localized using an affinity-purified antibody and paraffin sections of seven human eyes. An antibody for human serum albumin was used for comparison. The ANG was present selectively in the cytoplasm of the nonpigmented ciliary epithelium (NPCE), more prominently in the pars plana than in the pars plicata. Both ANG and albumin were present in the blood vessel lumina of the uvea and retina. Both antibodies also stained perivascular tissue in the uvea, but not in the retina, reflecting the relative tightness of blood-tissue barriers. The detection of ANG in the NPCE may be significant in view of previous descriptions localizing prorenin and angiotensin-converting enzyme in the same cell layer.

A murine model of herpes simplex virus-induced ocular disease for antiviral drug testing

Previous studies to determine the efficacy of new antiviral compounds in treating HSV ocular infections have used rabbit models. However, rabbits are expensive to purchase and maintain, and require the use of substantial amounts of test compounds. We have used the currently licensed antiviral trifluorothymidine in a murine model of HSV-induced ocular infection to demonstrate that the less expensive murine model can be used for the in vivo evaluation of potentially useful antiviral compounds. Treatment with TFT reduced the severity of blepharitis, vascularization of the cornea, stromal keratitis, and the percentage of animals developing symptoms. TFT treatment did not reduce the peak titers of infectious virus in the eyes of the infected animals, but did enhance clearance of virus from the tissues in a dose-dependent manner. Treatment with 1.0% TFT prevented the establishment of reactivatable latent infections. However, treatment with 0.01% or 0.1% TFT did not affect latency. The ED50 values for blepharitis, vascularization, and stromal keratitis ranged between 0.007% and 0.023%. These results are very similar to results obtained in rabbits and establish baseline data for comparing rabbit and murine models. This murine model provides a potentially less expensive alternative for in vivo drug testing.

Activation of NK cells in mice following corneal infection with herpes simplex virus type-1

Natural killer (NK) cells are large granular lymphocytes that mediate antigen nonspecific, non-major histocompatibility complex (MHC) restricted lysis of virus infected cells. They are thought to play a role in innate resistance to herpes simplex virus (HSV) infections. In most animal studies reported to date, the virus was injected intraperitoneally, not a natural route of infection. Using a murine model of acute HSV-1 ocular infection, we demonstrate that increased splenic NK activity is induced in BALB/c mice following corneal infection with four different strains of HSV-1. The kinetics of NK cell activation depended on the strain of virus and was associated with virulence of the strain and with the ability of the viruses to grow in vivo. We also assessed the role of interferon-alpha/beta, IFN-gamma, and interleukin-2 (IL-2) in the HSV-1 induced NK cell activation by treating mice with antisera against these lymphokines prior to infection. Treatment with anti-IFN-alpha/beta or anti-IFN-gamma significantly reduced NK cell cytotoxicity, suggesting that these lymphokines were involved in the activation of NK cells following HSV-1 ocular infection. Treatment with anti-IL-2 resulted in increased NK cell activity, suggesting that in vivo, IL-2 is involved in the suppression of NK cell activity in infected mice. Treatment with a combination of anti-IL-2 and anti-IFN also increased NK cytotoxicity. Despite the induction of high levels of NK activity, mice developed severe ocular disease or died of encephalitis.

Susceptibility of +/+, +/nu and nu/nu BALB/c mice to ocular herpes simplex virus infection

Athymic (nude) mice have played an important role in defining the function of the immune system and its role in infectious diseases. In the majority of these studies, heterozygous +/nu mice have been used as normal controls for the nu/nu mice, and it has been assumed that +/nu mice have essentially normal immune systems. We have compared the response of +/+, +/nu and nu/nu BALB/c mice following ocular infection with HSV-1 and have found that +/nu mice develop significantly more severe blepharitis, vascularization of the cornea, stromal keratitis and extraocular disease (herpetiform spread) than +/+ BALB/c mice. The extraocular disease was particularly severe in the +/nu mice, suggesting that factors regulating herpetiform spread of the virus are deficient in these mice. Susceptibility to lethal encephalitis did not differ between +/+ and +/nu mice. These results suggest that significant differences exist in the response to ocular HSV infection between +/+ and +/nu mice.

Mixed ocular infections identify strains of herpes simplex virus for use in genetic studies

Studies on the genetic mechanisms involved in the ocular virulence of herpes simplex virus (HSV) require the careful selection of parental strains. We used the technique of mixed ocular infection in vivo to identify strains of HSV for use in genetic studies. A pair of viruses (OD4 and 994) were identified that cause significantly more severe ocular disease when mixed together and used to infect the eyes of Balb/c mice compared to each strain when used alone. The mixed infection with OD4 and 994 did not result in increased neurovirulence. The technique of mixed ocular infections provides a sensitive screen to identify strains of virus that can act synergistically to cause more severe disease. Marker transfer can then be used to map the genes involved.

The HSV-1 UL45 gene product is not required for growth in Vero cells

We have constructed a HSV-1 UL45 null mutant (UL45 delta) by inserting a TK-lacZ cassette into a BclI site near the 5' end of the UL45 gene. A polyclonal antiserum produced to an Escherichia coli trpE:UL45 fusion protein was used to show that an 18-kDa polypeptide corresponding to the predicted UL45 gene product was produced in HSV-1 strain KOS-infected Vero cells but was not detected in UL45 delta-infected Vero cells. The absence of the 18-kDa protein had only a slight effect on viral growth in cell culture, indicating that the UL45 gene product is not essential for growth in Vero cells. However, the burst size of UL45 delta was smaller than HSV-1 KOS in Vero and HeLa cells. UL45 delta also had a smaller plaque size and an altered plaque morphology.

The herpes simplex virus ribonucleotide reductase is required for ocular virulence

We used a herpes simplex virus (HSV) type 1 ribonucleotide reductase (RR) null mutant (ICP6 delta) to study the role of HSV-1 RR in ocular HSV infections. We found that ICP6 delta was unable to induce vascularization of the cornea or stromal keratitis following inoculation into the cornea of BALB/c mice, but was able to induce a transient mild blepharitis. The parental strain (HSV-1 KOS) and a revertant of ICP6 delta, ICP6 delta+3.1, both caused severe ocular disease, indicating that HSV-1 RR is required for ocular virulence in mice. ICP6 delta grew poorly in vitro (Vero and BALB/c 3T3 fibroblasts) and in vivo (eye, trigeminal ganglia and brain) compared to ICP6 delta+3.1 and HSV-1 KOS, suggesting that the avirulence of ICP6 delta is due to poor growth in the host. ICP6 delta also grew less well in primary human corneal fibroblasts, suggesting that RR may be required for virulence in humans. These results indicate that drugs inhibiting the function of RR might be effective in treating ocular HSV infections.

Mixed infection with herpes simplex virus type 1 generates recombinants with increased ocular and neurovirulence

The authors used the method of mixed ocular infection and subsequent in vivo selection to isolate Herpes simplex virus type 1 intratypic recombinants with increased ocular virulence and neurovirulence. Four recombinants were studied in some detail (DRG1A3, DRG2A2, DRG3A3, and DRG4A1). The recombinants had lethal doses in 50% of animals tested (LD50) at least 2-3 log units lower than either parent virus (OD4 and CJ394) and caused significantly more severe stromal keratitis, vascularization of the cornea, and blepharitis than either parent. Studies on the ability of DRG1A3 and DRG4A1 to replicate in the eye, trigeminal ganglia, and brain showed that these recombinants replicated to higher titers (1-3.5 log units) than the parents in all three tissues. One of the parents, OD4, spread to the central nervous system with the same kinetics as CJ394, DRG1A3, and DRG4A1 but had a restricted ability to replicate in all tissues, which may account for its lack of virulence. The other parent, CJ394, was nonneurovirulent but replicated to titers which were only 1-1.5 log units lower than the neurovirulent recombinants. These recombinants should be useful in studying virulence determinants in herpetic ocular infections.

In vivo induction of Ia expression in murine cornea after intravitreal injection of interferon-gamma

Intravitreal injection of interferon gamma (IFN-gamma) induces increased expression of Class II major histocompatibility complex (Ia) antigen expression on corneal endothelial cells and stromal fibroblasts. In contrast, IFN-gamma has no detectable effect on Ia antigen expression in epithelium. Induction of Ia antigen expression was rapid with increases detectable as early as 6-12 hours after a single injection of 1 x 10(5) units. Expression peaked at 24-48 hours and decreased to background levels by 120 hours. The Ia antigen expression increased in a dose-dependent manner, and IFN-gamma treatment also induced the synthesis of increased amounts of a 65-kilodalton (kD) protein in the cornea. Increased levels of this 65-kd protein are seen as early as 12 hours after treatment and can be induced with as little as 1 x 10(2) units of IFN-gamma. The function of the 65-kd protein is unknown. This model should be useful in studies on in vivo modulation of Ia antigen expression.

Herpes simplex virus stromal keratitis is not titer-dependent and does not correlate with neurovirulence

We developed a murine model of ocular herpes simplex virus (HSV) disease which is particularly suited for testing stromal keratitis because most animals show some evidence of infection. Using this model, we characterized the ocular disease patterns caused by ten recent low-passage clinical isolates of HSV-1, as well as those caused by the established laboratory strains HSV-1 KOS and HSV-2 333. Viral strains were evaluated for their ability to cause stromal keratitis, blepharitis, vascularization of the cornea, and mortality. The model was not useful for scoring epithelial keratitis. The ocular disease caused by the recent isolates ranged from very mild disease to severe stromal keratitis. Some of the recent isolates caused disease as severe as the two laboratory strains. A comparison of the virulence characteristics expressed by various HSV strains indicated that the ability to cause stromal disease was correlated with vascularization of the cornea (correlation coefficient = 0.797, P less than 0.001) and was not correlated with the neurovirulence of the strains (correlation coefficient 0.045, P greater than 0.05). The severity of stromal keratitis was not dependent on the amount of inoculum over the range tested and a strain causing severe stromal keratitis caused severe ocular disease even when mixed with a nonstromal strain at ratios of 10:1, 100:1, and 1000:1.

Plasmid mediated mutagenesis of a cellular gene in transfected eukaryotic cells

NIH3T3 cells are widely used in transformation assays and readily take up transfected DNA. A system has been devised using NIH3T3 cells to measure the mutagenic effect of transfected DNA on recipient cell genes. NIH3T3 cells can be mutated to 6-thioguanine resistance at a frequency which suggests that at least a portion of the cells have only one functional copy of the HGPRT gene. They have a low spontaneous background mutation frequency (approximately 1 X 10(-7)). Transfection of three different plasmids into NIH3T3 cells induced 6-thioguanine resistant mutants at frequencies ranging from 3 to 11 fold above background. The mutant phenotype is stable and reversion frequencies of several mutants are less than or equal to 1 X 10(-7). Southern blot analysis of the HGPRT gene in several mutants showed that 4 of 26 mutants (15.4%) had detectable alterations in the structure of the HGPRT gene. Interestingly 3 of the 4 mutants showing rearrangements were obtained by transfection of the HSV-2 morphological transforming region.

Loss of a consensus splice signal in a mutant immunoglobulin gene eliminates the CH1 domain exon from the mRNA

A series of mouse myeloma mutants, derived from a cell line of the murine MPC-11 tumor (gamma 2b, kappa), resemble human heavy-chain disease in their loss of an internal domain (exon). In these mutants, most of the gamma 2b CH1 exon was present in the nuclear RNA but was removed during splicing to form the mature cytoplasmic RNA. Amino acid sequence studies of one mutant (10.1) are consistent with the loss of the complete CH1 domain. A second mutant cell line (I17) derived from 10.1 and containing the same CH1 alteration was shown by S1 nuclease protection experiments to have an additional mRNA deletion spanning the CH2-CH3 domain boundary. This second deletion was shown to result from a genomic alteration that provided a marker for the isolation of the expressed H-chain allele. To determine the basis of the CH1 splicing defect, the 117 genome-expressed gamma 2b constant region DNA was cloned. Sequence studies showed a deletion of 99 nucleotides around the 3' end of the CH1 domain, which removed the splice site and flanking DNA, apparently causing the aberrant splicing of the RNA transcript. The sequence deleted in the mutant is flanked by short repeats of the octameric sequence CCAGCCAG in the wild-type gene. In the mutant, one copy of the repeat, in addition to the sequences between the repeats, has been lost.

Recent duplication and germ-line diversification of rat immunoglobulin kappa chain gene joining segments

Sequence determination of the joining segment gene (J) cluster in the kappa chain (J kappa) in the embryonic context demonstrates that rat genome contains seven J kappa gene segments that expanded from an ancestral cluster of five J kappa genes. The rat J segments are separated by about 300 base pairs (bp) and are flanked 5' by the presumed variable region (V)/J recombination signal sequence and 3' by the RNA splicing signal. Two of the J gene segments designated J2A and J2B and their 5'-flanking spacer DNA bear striking homology to J2 and its 5'-flanking spacer. Thus, the unit of duplication was the entire J kappa coding region and 5' noncoding spacer (345 bp). The duplication probably occurred as two separate unequal crossing-over (UXO) events. The first UXO event can be confined to recombination within an identical stretch (14 bp long) located at the 3' ends of the coding regions of J1 and J2. The second event could involve a longer segment (372 bp) of tight homology generated by the first UXO event, thus increasing the probability of repeated expansion of the same DNA segment. The sequence homology among the rat duplicated segments (98-99%) is larger than the homology between the corresponding rat and mouse segments (89%), showing that the rat J kappa gene expansion must have occurred after rat and mouse divergence 10 X 10(6) yr ago. We estimate that the first and second UXO events occurred 2 X 10(6) and 1 X 10(6) yr ago, respectively. J3 of rat and mouse share the same mutation (G leads to C) in the RNA splicing signal that presumably inactivates J3. This mutation preceded divergence of the two species. A mutation in the first nucleotide of codon 96 has occurred in both duplicated segments, the only position along 345 bp where J2, J2A, and J2B differ from each other. This results in three different amino acids at position 96 not present in any other J kappa. These mutations are physiologically significant because they diversify the third complementarity-determining region (CDR3) and, thus, may reflect selective pressure to increase antibody diversity. The germ-line diversification of CDR3 was exercised within the last 1-2 X 10(6) yr.

Somatic DNA rearrangement generates functional rat immunoglobulin kappa chain genes: the J kappa gene cluster is longer in rat than in mouse

The kappa immunoglobulin (Ig) genes from rat kidney and from rat myeloma cells were cloned and analyzed. In kidney DNA one C kappa species is observed by Southern blotting and cloning in phage vectors; this gene most likely represents the embryonic configuration. In the IR52 myeloma DNA two C kappa species are observed: one in the same configuration seen in kidney and one which has undergone a rearrangement. This somatic rearrangement has brought the expressed V region to within 2.7 kb 5' of the C kappa coding region; the rearrangement site is within the J kappa cluster which we have mapped. The rat somatic Ig rearrangement, therefore, closely resembles that seen in mouse Ig genes. In the rat embryonic fragment two J kappa segments were mapped at 2 and 4.3 kb 5' from the C kappa coding region. Therefore, the rat J kappa cluster extends over about 2.3 kb, a region much longer than the 1.4 kb of the mouse and human J kappa clusters. In the region between C kappa and the expressed J kappa of IR52 myeloma DNA, and XbaI site present in the embryonic kappa gene has been lost. A somatic mutation has therefore occurred in the intervening sequence DNA approx. 0.7 kb 3' from the V/J recombination site. Southern blots of rat kidney DNA hybridized with different rat V kappa probes showed non-overlapping sets of bands which correspond to different subgroups, each composed of 8-10 closely related V kappa genes.

An image reversal process for electron microscope film

An improved technique has been developed to produce a positive image directly on some standard electron microscope films (Kodak 4489, SO 163, and Ilford Electron Microscope Film). This technique has been useful for processing micrographs of freeze-etched and shadowed specimens, and eliminates the need for producing positive image transparencies before printing.