Evaluation of an ovine testis cell line (OA3.Ts) for propagation of capripoxvirus isolates and development of an immunostaining technique for viral plaque visualization.

An ovine testis cell line (OA3.Ts) was evaluated and compared with primary lamb kidney (LK) cells for its utility in capripoxvirus propagation and titration. A comparison of OA3.Ts cell growth kinetics and morphology at low (<33) and high (34-36) passage levels indicated a difference in both characteristics. However, viral titers determined in low and high passage OA3.Ts cells were comparable with those obtained using LK cells. Capripoxvirus infection of OA3.Ts and LK cells resulted in a similar cytopathic effect, which allowed for the detection of discrete viral plaques following immunostaining with capripoxvirus-specific antiserum.

Use of a Japanese quail fibrosarcoma cell line (QT-35) in serologic assays to determine the antigenic relationship of avian metapneumoviruses.

The ability of a Japanese quail fibrosarcoma cell line (QT-35) to support the replication of avian metapneumoviruses belonging to the 3 subgroups A (14/1 virus), B (Colorado virus), and C (Hungary virus) enabled the development of assays for the detection and evaluation of virus-specific antibodies. On the basis of the results of enzyme-linked immunosorbent assay (ELISA), plaque reduction neutralization assay (PRNA), immunofluorescent assay (IFA), and Western blot analysis, some degree of antigenic cross-reactivity was observed between prototype viruses belonging to each of the 3 subgroups A, B, and C. The antigen produced in QT-35 cells was found to be superior with respect to its reactivity with virus-specific antibodies, as determined when used in ELISA and IFA. Standardization of both the input virus and the virus-specific antibodies in PRNA enabled a more detailed analysis of the antigenic relationship between these viruses. Specifically, it was observed that 14/1 virus shared more neutralizing regions with Hungary and Colorado viruses than did either of these viruses with 14/1 virus. In addition, Hungary virus shared comparatively fewer neutralizing epitopes with the Colorado virus than did 14/1 virus. Western blot analysis of the reactivity patterns of virus antigen, produced in QT-35 cells, with subgroup-specific antibodies identified a cross-reactive protein migrating at approximately 18 kD. These assays and the information from the Western blot will enable further analysis of avian metapneumovirus isolates to determine antigenic relationships.

Plaque assay for avian metapneumovirus using a Japanese quail fibrosarcoma cell line (QT-35).

A plaque assay for detecting, isolating and titrating avian pneumoviruses using a Japanese quail fibrosarcoma cell line (QT-35) is described. Plaques are produced after application of either an agarose or carboxymethyl-cellulose (CMC) overlay onto cell monolayers infected with representative avian metapneumoviruses which belong to subgroup A, B or C. Virus plaques can be easily visualized by light microscopy or after staining. The parameters affecting plaque appearance include: cell seeding concentration, virus strain, overlay composition and incubation time following infection. Optimal conditions for plaquing involve seeding QT-35 cells at 40,000 cells per cm(2) when using a 1.5% CMC overlay or 100,000 cells per cm(2) when using a 1.0 or 0.8% agarose overlay. In both cases, cell monolayers are infected with virus 24 h post-seeding and clearly visible plaques develop in 6 days. Due to the robust nature of these cells, the incubation time can be extended to a maximum of 13 days after infection in order to produce larger plaques.

Evaluation of a Japanese quail fibrosarcoma cell line (QT-35) for use in the propagation and detection of metapneumovirus.

A Japanese quail fibrosarcoma cell line (QT-35) was evaluated and compared to Vero cells for its utility in metapneumovirus propagation, titration and serological detection by indirect immunofluorescence staining. Cell characteristics such as growth kinetics at different passage levels and seeding density in 96-well plates using various media formulations were studied in order to determine suitable assay parameters. Specifically, QT-35 cells supported the replication of a subgroup A metapneumovirus, strain 14/1, when maintained in DMEM containing a high level of glucose (4500 mg/l) and 2% gamma-irradiated fetal bovine serum (gamma-FBS). There appeared to be a decreased ability of metapneumovirus produced in chicken embryo fibroblast (CEF) cells to replicate to high titers in QT-35 cells, however, this apparent restriction was overcome after the second passage resulting in high titered stock. Metapneumovirus produced in Vero cells and propagated in QT-35 cells produced high titered stock after the first passage. Viral titers determined in Vero and QT-35 cells were comparable, when the latter cell line was used at passage levels < or = 20 and seeded between 5.0 x 10(4) and 1.0 x 10(5) cells/0.33 cm(2) in hgDMEM containing 10% gamma-FBS, with a reduction to 2% gamma-FBS when the virus was applied to the cell monolayers 24 h post-seeding. After infection with metapneumovirus, QT-35 cells exhibited syncytia, similar to those in metapneumovirus-infected Vero cells, which were readily detected by indirect immunofluorescent (IF) staining.