OBJECTIVE

To determine the effects of RSV infection on the development of lung inflammation and the expressions of T-helper cell related cytokines in Balb/c mice pre-sensitized with ovalbumin.

METHODS

Forty mice were randomly divided into four groups: (1) the control group: nonsensitized, noninfected; (2) the RSV group: nonsensitized, infected; (3) the OVA group: sensitized, noninfected; and (4) the OVA + RSV group: sensitized, infected (RSV 6.5 x 10(6) PFU nasal drip). Bronchoalveolar lavage (BAL) was performed in six mice from each group five days after RSV nasal inoculation. Cells in the BAL were counted and classified and the supernatants of the BALF were used for detection of IL-4 and IFN-gamma. Four mice in each group were sacrificed for lung RNA extraction, and IL-4, IL-5 and IFN-gamma mRNA levels were determined by RT-PCR.

RESULTS

(1) Total BAL cells from the RSV group [(14.5 +/- 5.4) x 10(6)/ml] and the OVA + RSV group [(16.8 +/- 4.9) x 10(6)/ml] were significantly higher than those in the control group [(7.7 +/- 2.4) x 10(6)/ml] and the OVA group [(9.0 +/- 2.5) x 10(6)/ml] (all P < 0.05), with more lymphocytes in the RSV group (0.63 +/- 0.05) and the OVA + RSV group (0.77 +/- 0.09) than the control group (0.28 +/- 0.05) (P < 0.05) and the OVA group (0.36 +/- 0.03) (P < 0.05). More eosinophils were found in the OVA + RSV group (0.0690 +/- 0.0100) than in the RSV group (0.0090 +/- 0.0050), the OVA group (0.0100 +/- 0.0040) and the control (0.0030 +/- 0.0010) (all P < 0.05). (2) Pulmonary inflammation in the OVA + RSV group and the RSV group was more severe than that in the OVA group and the control group. More lymphocyte infiltration was found in the OVA + RSV and the RSV groups. More eosinophils were found in the OVA + RSV group, but not in the other groups. (3) Expression of IL-4, IL-5, and IFN-gamma mRNA: IFN-gamma mRNA expression (1.05 +/- 0.12) was higher in the RSV group, than in the control (0.00 +/- 0.00). There were only minimal expression of IL-5 mRNA and no expression of IL-4 mRNA, indicating a Th1-like cytokine response. Expressions of IL-4 mRNA and IL-5 mRNA were significantly higher in the OVA + RSV group than in the other groups, but the IFN-gamma mRNA expression was less than that in the RSV group, indicating a Th2-like cytokine response. (4) IFN-gamma activation in BALF from the RSV group [(33.8 +/- 1.1) pg/ml] was significantly higher than that in the other groups (P < 0.05), while IL-4 showed no significant change as compared to the control group. The level of IL-4 in the OVA + RSV group [(24.0 +/- 1.5) pg/ml] was significantly higher than that in all the other groups (P < 0.05).

CONCLUSION

RSV infection in OVA-sensitized Balb/c mice caused a different immune response from that caused by RSV infection in nonsensitized mice. RSV infection alone resulted in a Th1-like cytokine response, while infection after OVA sensitization resulted in a Th2-like response.