Inhibition of interferon production by chloroquine diphosphate

Chloroquine enhances replication of influenza A virus A/WSN/33 (H1N1) in dose-, time-, and MOI-dependent manners in human lung epithelial cells A549

Anti-malaria drug, chloroquine, has been reported to be effective against influenza A virus (IAV) in vitro and used in in-vivo experiments and clinical trial for prevention or treatment of influenza. In this study, it has been shown by immunofluorescence, hemagglutination, and plaque assays that chloroquine enhanced A/WSN/33 (H1N1) replication with pronounced cytopathic effect in dose-, time-, and MOI-dependent manners in human lung epithelial cells A549. Time-of-addition assay showed that inhibitory effect on virus replication by chloroquine pre-treatment was indistinctive, and virus productions were enhanced when the drug was applied after viral adsorption. The effectiveness of chloroquine as an anti-influenza drug is questioned, and caution in its use is recommended.

Antiviral effects of 2',5'oligoadenylates (2-5As), and related compounds

Dephosphorylated "core" of 2',5'-oligoadenylate (2-5A) dimer (A2'p5'A), exogenously added to nonpermeabilized FL cells, inhibited the multiplication of Sindbis virus and vesicular stomatitis virus (VSV). The compound was shown to inhibit viral protein synthesis. The addition of A2'p5'A at the early stage of viral replication was more effective than that at the late stage. In contrast with the core, phosphorylated 2-5A (p5'A2'p5'A and ppp5'A2'p5'A) and 2-5A analogs containing cordycepin (3'-deoxyadenosine) did not show such antiviral effects. The rate of uptake of [3H]ppp5'A 2'p5'A into acid-soluble and acid-insoluble fractions, especially into the acid-insoluble fraction, was faster than that of [3H]A2'p5'A. These results suggest that the difference of antiviral activity between A2'p5'A and ppp5'A2'p5'A does not result from the different rate of uptake by cells, but from the different rate of from acid-soluble to acid-insoluble fractions.

A temperature-sensitive mutant of Newcastle disease virus defective in intracellular processing of fusion protein

A temperature-sensitive mutant (ts3) of Newcastle disease virus was physiologically characterized. All major viral structural proteins were synthesized at the permissive (37 degrees C) and nonpermissive (42 degrees C) temperatures, but the fusion (F) glycoprotein was not cleaved at 42 degrees C. In immunocytochemical electron microscopy, the F protein was abundant in the rough endoplasmic reticulum but not in cytoplasmic membrane at 42 degrees C. Noninfectious hemagglutinating virus particles containing all major structural proteins except the F protein were released at 42 degrees C from infected cells. We concluded that the defect in ts3 resides in the intracellular processing of the F protein.

The interferon compartment of the immune response in human malaria: II. Presence of serum-interferon gamma following the acute attack

The present study concerns the monitoring of serum-interferon (serum-IFN) levels among 189 patients followed after and sometimes during an acute episode of malaria due mainly to Plasmodium falciparum (P. falciparum). Of these patients, 110 known to have no other parasitic or infectious disease were followed in France; 79 were from Thailand, among which 25 cases of neuromalaria were diagnosed. In a first four-month survey conducted in France, among 100 patients seen after the acute attack, serum-IFN-gamma was characterized among 87% cases for which at least two sera were controlled, whereas in a healthy population no serum-IFN was present. When efforts were concentrated on screening ten cases during the first 48 h of the febrile attack, serum-IFN-alpha was mainly characterized, whereas serum-IFN-gamma was present only once. Elevated leukocyte 2',5' oligoadenylate synthetase levels were found among several IFN-alpha positive patients of this study group. A peculiarity pertaining to the patients from Thailand was that one-third (25 cases) were cerebral malaria cases. Among these, 15 were followed under hospitalization during the first 96 h. In this study group, the onset of circulating immune interferon was found to be preceded or accompanied by that of IFN-alpha. Thus, if serum-IFN-gamma is largely characterized among malaria patients followed after the acute attack, it is possible that the onset of circulating immune interferon is generally preceded by that of IFN-alpha.

Interferon induction by viruses. XI. Early events in the induction process

The mechanism by which NDV, Sindbis virus, and VSV enter "aged" primary chick embryo cells to initiate IFN induction was studied by using NH4Cl, a lysosomotropic weak base that compromises low pH-dependent membrane fusion. NH4Cl was used to perturb the early steps in virus entry into the cytosol thought to result ultimately in presentation of dsRNA to the cell's first-stage recognition system for IFN induction. Three parameters were monitored: (i) the nature of the dose (multiplicity)-response (IFN yield) curve, (ii) the activity of IFN-inducing particles (IFP), and (iii) the quantum yield of IFN. In all tests, the qualitative nature of the dose-response curve was not altered by NH4Cl treatment. NH4Cl had no effect on infectivity of IFN induction by NDV in keeping with a mode of entry involving acidic-independent fusion through the plasma membrane. Sindbis virus infectivity and IFN-inducing particle activity were inhibited similarly in an NH4Cl concentration-dependent manner. While the infectivity of VSV was very sensitive to the action of NH4Cl, virtually all IFN-inducing particles were functional; however, the quantum yield of IFN they induced was reduced in an NH4Cl concentration-dependent manner. Only 1 of 6 VSV [+/-]DI-011 particles registered in NH4Cl-treated cells; however, they induced more than one-half the normal quantum yield of IFN. The mechanism of entry of Sindbis virus (acidic-fusion) and VSV (acidic-endocytosis) was distinguished by the action of cytochalasin B. Infectivity and IFN induction by Sindbis virus and VSV share a common, limiting step in NH4Cl treated cells: transfer of viral RNA from basic vacuoles into the cell cytosol. The similar sensitivity of Sindbis IFP and PFP to NH4Cl suggests that both activities respond the same to increased intravacuolar pH; neither can be expressed. VSV-IFP, requiring only partial genomic expression (or none in the case of DI-011) can register in NH4Cl-treated cells to varying degrees under conditions that prevent expression of the full genome.

Binding of polyriboinosinic-polyribocytidylic acid with cultured cells

Homogenates prepared from polyriboinosinic-polyribocytidylic acid copolymer [poly(rI) - poly(rC)]-treated cells exhibited antiviral activity in chick embryo, L and rabbit kidney cells. The antiviral activity in the homogenate co-sedimented with cellular membrane material and was shown to be poly(rI) - poly(rC) by a hybridization competition test with immobilized polyribocytidylic acid. The results indicate that poly(rI) - poly(rC) binds firmly to cellular membrane. These studies, however, could not differentiate between specific binding leading to the interferon induction and non-specific binding possibly unrelated to the induction of interferon.