Low vitamin A (VA) levels have been detected in serum from sick RSV-infected infants. Due to its role in immunity and epithelial regeneration, prophylactic VA administration may affect the course of RSV infection. OBJECTIVE: To determine the effect of high dose VA prophylaxis on the histopathologic damage and viral load in the lung, in experimental RSV infection in BALB/c mice. METHODS: Three groups of BALB/c mice were studied (A+, n=5; A-, n=5; C, n=4). In week five of life, mice in group A+ and A- received 12,000 units of VA or placebo, respectively, by intraperitoneal(IP) route. Two weeks later, both groups were inoculated intranasally with 1×106 PFUs of RSV (Long strain). Group C (n=4) was not treated IP nor inoculated with RSV. Six days postinfection mice were sacrificed. The left anterior lobe was used for viral lung titration and the right lung to evaluate histopathologic damage according to a modified score by Connors et al. An index of lung damage was calculated by dividing the number of bronchioli with a score 5-6 (severe lung damage) over the total number of studied bronchioli×100. Retinol levels were determined by HPLC in sera obtained prior to sacrifice. RESULTS: The mean±SE of the lung viral titers, expressed as log PFU/g lung tissue, was 4.52±0.18 and 4.18±0.13, in groups A+ and A-, respectively (p>0.1). The mean index±SD of lung damage was 9.6±5.7 and 42±15, in groups A+ and A-, respectively(p<0.05). Group C did not have lung injury attributed to infection. Serum levels of retinol were 428±203 and 365±175 ng/ml in groups A+ and A-, respectively (p>0.1). CONCLUSIONS: 1) In this experimental model of RSV infection, the viral titer in the lung was not modified by VA prophylaxis, 2) The histopathologic damage associated to RSV infection was significantly less severe in the group of mice pretreated with VA.
