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Background: Human metapneumovirus and respiratory syncytial virus can cause severe respiratory diseases, especially in infants, young children, and the elderly. So far it remains unclear why infections in the elderly become life threatening despite the presence of neutralizing antibodies in the serum, and to which extent double infections worsen the clinical course. Methods: Young and aged BALB/c-mice were infected with RSV or/and HMPV. Appearance of the mice was observed during course of infection. On day 5 p.i. animals were dispatched by cervical dislocation and levels of TNF-α and NF-κB were determined. Results: The observation of activity, weight and appearance of the different mice showed no differences among the tested groups. Despite this, the immunologic response depends on the animals' age and the virus they were infected with. In young animals, NF-κB levels were elevated if infected with HMPV and HMPV/RSV but remained low in RSV infections, whereas in aged animals the opposite was observed: solely RSV-infected animals showed elevated levels of NF-κB. TNF-α was slightly elevated in HMPV-infected young and old animals, but only in young animals this elevation was significant. Conclusions: Contrary to other studies, no weight loss or change in activity despite productive lung infection with the different viruses were observed. This may be due to the weaker anaesthesia or the lesser volume of virus solution used, leading to less stress in the animals. The observed differences in TNF-α and NF-κB elevation lead to the assumption that young and old individuals have different mechanisms to react against the viruses. [ABSTRACT FROM AUTHOR]

Abstract: Human metapneumovirus (hMPV) and human respiratory syncytial (RSV) virus cause mild to severe infections of the respiratory tract in all age groups. So far, several cell lines derived from respiratory tissues have been identified to support replication of both viruses. Unfortunately, titers attained during replication differ between the both viruses within one cell line despite equal infection conditions, on the one hand giving raise to the assumption that the individual susceptibility may vary in dependence of the virus, and, on the other hand, making it difficult to compare results between both viruses. Low titers may cause problems in experiments such as animal trials, in which high titers in low volumes are a prerequisite for successful experiments. The advantages are described of the use of a human cell line (normally used for hepatitis viruses research) susceptible for RSV and hMPV in which both viruses replicate to comparable and high titers. It is also shown that the cell line can also be used for applications such as cell viability tests. Cell viability tests can be used as reciprocal determination tests of viral titers and therefore offer the opportunity to replace classical virological tests such as TCID50. The cell line can be also used for high throughput applications like drug screening, making it a useful tool for screening for antiviral compound active against RSV and hMPV. [Copyright &y& Elsevier]