Indra P. Singh

Broad antiviral activity in tissues of crustaceans

Innate antiviral substances occur in vertebrates and may function as host defenses. Virus infections are common among invertebrates, but little is known about the ability of invertebrates to control viral infections. Pre-existing antiviral substances may be particularly important, since invertebrates lack the antiviral defense conferred by specific immunity. In our study, we found that tissue extracts of blue crab (Callinectes sapidus), shrimp (Penaeus setiferus), and crayfish (Procambarus clarkii) contained antiviral activities that inhibit a variety of DNA and RNA viruses, i.e. Sindbis virus (SB), vaccinia virus (VAC), vesicular stomatitis virus (VS), mengo virus (MENGO), banzi virus (BANZI) and poliomyelitis (POLIO). The concentration of inhibitory activity was relatively high, ranging from 102 to 216 U/g tissue for Sindbis virus, using the various tissue extracts. The other viruses were somewhat less sensitive to the inhibitor. The main antiviral activity in the inhibitor preparation from blue crab resided in an approximately 440 kDa fraction. It was inactivated significantly by lipid extraction, but not by proteinase K or glycosidases. The antiviral mechanism of the inhibitor from the blue crab was inhibition of virus attachment to eukaryotic cells, as evidenced by inhibitory activity at 4 degrees C. These studies are among the first to show the existence of broadly active antiviral activities in aquatic crustaceans. These antiviral substances may function as innate host defenses in these species that lack specific antibody immunity and, therefore, merit further study.

Lipoproteins account for part of the broad non-specific antiviral activity of human serum.

Several antiviral substances have been detected in human serum but few have been shown to possess broad antiviral activity. These broadly active antiviral molecules could be of significance as innate defense mechanisms. We have previously identified and characterized a broadly antiviral glycoprotein, UTI3, which accounts for 50 antiviral units/ml of human and mammalian sera. In addition there are reports of antiviral activity of human serum apolipoprotein A-1 (apo A-1), an important constituent of high density lipoprotein (HDL), against human immunodeficiency virus (HIV) and herpesvirus. Therefore we investigated (1) whether HDL is broadly antiviral, (2) how much of the broad antiviral activity of serum is due to HDL, and (3) the mechanism(s) of HDLs antiviral action. In this paper we report that (1) HDL does have broad antiviral activity, (2) HDL accounts for a modest but significant portion of the antiviral activity of serum, and (3) HDL acts by preventing virus penetration. Overall, HDL may be one of the broadly antiviral defences in the bloodstream.

Postinfection therapy of arbovirus infections in mice.

Most antiviral agents are efficacious prophylactically in vivo, and a few are efficacious for postinfection (p.i.) therapy. To explore possibilities for p.i. therapy of encephalogenic Banzi virus (BZV) and Semliki Forest virus infections in mice, we evaluated candidate antiviral therapies after development of the first clinical signs of infection. The earliest clinical indication of BZV viremia in mice is a rise in core body temperature beginning on day 3 p.i. BZV-infected mice showing elevated core body temperatures (greater than or equal to 37.3 degrees C) on days 3 and 4 p.i. were treated intraperitoneally with the interferon inducer poly(ICLC) (80 micrograms per mouse) and/or specific antiserum. Combined therapy on day 3 of a BZV infection protected over 75% of mice showing clinical evidence of viral disease before treatment. Protection against early brain infection must occur on day 4 p.i., since by that day BZV has started multiplying in the brains of the mice. Significant protection occurred with antiserum alone and increased with poly(ICLC). Similar protection was obtained during Semliki Forest virus viremia, but this infection is so rapid that the first clinical signs are reliably detectable only after viremia. Images

Innate antiviral defenses in body fluids and tissues.

Abstract Innate, non-specific, resistance mechanisms are important barriers to pathogens, particularly delaying virus multiplication at the onset of infections. These innate defense mechanisms include a series of mechanical barriers, pre-existing inhibitory molecules, and cellular responses with antimicrobial activity. The antiviral activities of these innate inhibitors reside in a variety of partly characterized substances. This review presents the innate antiviral inhibitors in cell cultures, urine, serum, the gastrointestinal tract, the nervous system, tissues of crustaceans, and saliva. Medical adaptation of the innate antiviral defense mechanisms may be useful for prevention and treatment of viral infections.

Innate defences against viraemia.

Human blood plasma has been reported to possess nonspecific antiviral activity. This activity is due to several preexisting naturally occurring molecules that are either active against individual members or a family of viruses. These molecules, however, have not been adequately studied to reveal their molecular structures and mechanisms of action presumably because of their low and nonspecific antiviral action. Therefore, their possible role against viraemia remains unknown. Recently, two naturally occurring nonspecific broad‐spectrum antiviral agents, University of Texas Inhibitor β (UTIβ) glycoprotein and high density lipoprotein, have been described in human serum. They are active against DNA and RNA viruses and one of them, UTIβ, possesses significant antiviral activity of 40 units/mL. Since preexisting antiviral molecules in serum appear to be the only defence mechanisms available at the onset of viral infection they may have protective significance against viraemia. In view of this potential, we have undertaken to review the properties of these innate viral inhibitory molecules. Copyright

Vertebrate brains contain a broadly active antiviral substance

Brain tissue extracts from vertebrates were examined for non-specific, broad-spectrum virus inhibitors, previously identified and characterized from other body tissues and fluids. An antiviral activity found in human, bovine, ovine, porcine, lapine, murine and piscine brain tissues shares some properties with a contact blocking-virus inhibitor, which was previously found only in cell culture supernatants. The inhibitor was active against (in order of sensitivity to inhibitor) Banzi, Sindbis, Bunyamwera, Newcastle disease, herpes simplex I, Semliki forest, polio I, mengo, vaccinia and vesicular stomatitis viruses. It is approximately 4000 kDa and possesses a complex structure containing protein, carbohydrate and lipid moieties. The inhibitor does not directly neutralize virus or induce an antiviral state in cells, but appears to act early in the replication cycle, most likely by preventing virus attachment to target cells. Its occurrence in concentrations sufficient to reduce virus yield in cell cultures at least 30-fold may indicate a role in limiting viral infections of the central nervous system.

A HOST DEFENSE ROLE FOR A NATURAL ANTIVIRAL SUBSTANCE IN THE NERVOUS SYSTEM

The pathogenesis of virus infections of the nervous system (NS) is regulated by host defenses. The defensive role of a major constitutive antiviral substance was studied by determining its distribution in the human nervous system, its concentration and the ability of this viral inhibitor to protect mice against viral infection. The 4000 kDa inhibitor complex in the human nervous system was detected in brain gray and white matter, spinal cord, and sciatic nerve but not in human cerebrospinal fluid. The inhibitor was found in the extracellular medium incubated with minced murine brain. The inhibitory titer ranged from approximately 50 to 200 antiviral units per gram against polio 1, Semliki Forest, Banzi, mengo, Newcastle disease and herpes simplex 1 viruses. The inhibitor is composed of lipid and essential protein and carbohydrate moieties as determined by enzymatic inactivation. Protection of inhibitor-treated mice was demonstrated against both an alphavirus and a picornavirus. Thus a natural defensive role for the broadly antiviral inhibitor is suggested by its constitutively high concentration, wide distribution in nervous system tissues, presence in extracellular fluid and its ability to provide protection in infected mice.

Innate gastrointestinal immunity: characterization of broadly active viral inhibitors.

Abstract Innate viral inhibitors that are broadly active have been characterized in the serum and the nervous system, but incompletely characterized in the gastrointestinal (GI) tract. GI preparations from porcine gastric mucosa, mouse intestine, and in neuramide (a pharmaceutical product), were examined for broad antiviral activity, molecular size and mechanism of action for comparison with the previously characterized, innate inhibitors in the serum and nervous system. The GI inhibitors were found to be active in high titers against RNA and DNA viruses, resistant to proteolysis, glycolysis, lipid extraction and possessed differing mechanisms of action. The mouse intestinal inhibitor prevented virus attachment to cells, and neuramide acted at an early post-attachment stage of virus multiplication. The porcine mucosal inhibitor acted as late as 6 h after initiation of the multiplication cycle. These broadly active GI inhibitors differed from the previously described serum inhibitor (UTIβ) high density lipoproteins (HDL) and the nervous system (NS) inhibitor by being smaller (600±400 kDa) and resistant to proteinase K, glycosidases and organic solvents. The mouse intestinal inhibitor acts similarly to UTIβ and NS inhibitor by preventing attachment of virus to the cells. In comparison, the neuramide and the porcine mucosal inhibitor, like HDL, acted after attachment to the target cells. The innate nonspecific, broadly-active virus inhibitors, based on high titers and location, are considered important initial immune defense mechanisms against viral infections and thus potentially useful in medical applications.