In vivo production of tumour necrosis factor-α and interleukin-6 in BALB/c mice inoculated intranasally with a high dose of respiratory syncytial virus

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Abstract
Intranasal administration of an inoculum of 107 focus‐forming units (FFU) of respiratory syncy‐tial (RS) virus induced disease in BALB/c mice with signs of anorexia, cachexia, ruffled fur, and pneumonia. Mice displayed mild signs of illness on day 1 postinoculation (PI), followed by a transient recovery phase of 3 days. Disease rapidly reappeared on day 5 PI and worsened on subsequent days, with mortalities by day 7 PI. Mice inoculated with 5 × 106 FFU exhibited milder signs of disease, while those inoculated with 2 × 106 FFU and control mice given only Hep‐2c cell suspension exhibited no noticeable signs of illness. High levels of bioactive tumour necrosis factor‐a (TNF‐a) and interleukin‐6 (IL‐6) were detected in both lungs and sera of mice inoculated with 107 FFU of virus. Peak levels of both cyto‐kines were detected at day 1 PI but remained detectable throughout the 7 day period studied postinoculation. Cytokine levels were much lower or were undetectable in control mice. These results suggest that the macrophage is stimulated in vivo to produce inflammatory cy‐tokines in response to RS virus infection.