Analysis of variance was used to compare the effects of the challenge strain on coughing, average daily weight gain, severity of pneumonic lesions and cytokine responses. Prior to analysis, data for coughing scores,percentage affected lung by weight, Goodwin lung scores and IL-6 concentrations in TBLF were transformed (by taking the square root of coughing scores and log10 of the percentage affected lung by weight, Goodwin lung scores and IL-6 concentrations) to reduce variance heterogeneity in diagnostic variables.