Swine testis cells contain functional heparan sulfate but are defective in entry of herpes simplex virus

Herpes simplex virus (HSV) enters and infects most cultured cells. We have found that swine testis cells (ST) produce yields of infectious HSV-1 up to four orders of magnitude lower than those of human embryonic lung (HEL) and HEp-2 cells because of a defect in virus entry. For ST cells, virus binding is reduced, DNA from input virus cannot be detected, and virus proteins are not synthesized. Polyethylene glycol treatment of ST cells after exposure to HSV allows viral entry, protein synthesis, and productive infection. Transfection of viral genomic DNA that bypasses the normal entry process produces similar yields of infectious virus from ST, HEL, and HEp-2 cells. Therefore, all three cell lines can support the HSV replicative cycle. Biochemical analyses and inhibition of sulfation by sodium chlorate treatment show that ST cells contain amounts and types of heparan sulfate (HS) similar to those of highly susceptible cells. HSV infection of sodium chlorate-treated HEL and ST cells indicates the presence of a second, non-HS receptor(s) on susceptible HEp-2 and HEL cells that is missing, or not functional, on poorly susceptible ST cells. We conclude that ST cells are defective in HSV entry, contain functional HS, but lack a functional non-HS receptor(s) required for efficient HSV-1 entry. Further, ST cells provide a novel resource that can be used to identify, isolate, and characterize an HSV non-HS receptor(s) and its role in the entry and tropism of this important human pathogen.

Cell-specific kinetics and efficiency of herpes simplex virus type 1 entry are determined by two distinct phases of attachment

We previously provided evidence for a model of herpes simplex virus type 1 (HSV-1) entry by a cascade of interactions between components of the virion envelope and cellular plasma membrane (Fuller and Lee, 1992, J. Virol. 66, 5002-5012). In this report we have determined entry kinetics of wild-type HSV-1 into two highly susceptible cell lines to further explore the contributions of viral or cellular factors to entry. Penetration rates of preattached virus varied among several common laboratory HSV-1 strains into one cell line. However, entry kinetics varied substantially for a single strain into highly susceptible HEp-2 or Vero cells under identical conditions. Plaquing efficiencies and sensitivity to heparin also significantly differed between these cells. Kinetics of entry that included virus attachment and penetration showed that the cell-specific effects can be explained by two distinct phases of attachment that occurred before penetration, but differed in duration on both susceptible cell lines. Initial attachment of virus is resistant to removal with phosphate-buffered saline, but sensitive to removal with buffer containing heparin. This is followed by a second type of attachment that is heparin resistant, but still sensitive to extracellular inactivation. We conclude that although undefined factors unique to individual wild-type HSV-1 laboratory strains affect entry kinetics, entry of any one strain is greatly influenced by interactions of virus with specific cell components during at least two distinct phases of attachment before penetration. Moreover, the second phase to stabilize binding seems to be the rate-limiting event in entry. Since major differences in the amounts or sulfation patterns of heparan sulfate were not detected, differences in the surfaces of HEp-2 and Vero cells that influence the kinetics and efficiency of HSV-1 entry are likely in the fine structure of heparan sulfate or in the presence and quantity of other unidentified receptors.

Role of horse flies in transmission of wquine infectious anemia from carrier ponies

Equine infectious anemia virus was transmitted from an acutely ill and an inapparently infected pony to uninfected ponies by the interrupted feeding of horse flies (tabanids). Transmission from acutely ill ponies was not accomplished following: (1) the interrupted feeding of a single horse fly, (2) bites of horse flies that had fed on an acutely affected pony 24 hours earlier, (3) bites of horse flies that had oviposited after feeding on an acutely affected pony, or (4) the inoculation of larval material derived from horse flies that had fed to repletion. It was concluded that horse fly transmission of equine infectious anemia virus is mechanical only and that infected horses that are free of clinical signs can be a source of virus for insect transmission.