Fig. 3.

Association between IL-1β gene expression and lung tumor development. Mice were treated with NNK plus silica. At 16 weeks, the incidence of lung tumors was quantified histologically, whereas cytokine mRNA levels were measured by reverse transcription–PCR in lung tissue homogenates. Tumor multiplicity versus IL-1β mRNA levels (normalized to GAPDH) from mice in four independent experiments (N = 23) is shown. The solid trend line and P value were calculated using the maximum likelihood estimate derived from a Poisson linear analysis. Note that IL-1β mRNA levels did not vary as a function of tumor multiplicity in mice treated with NNK alone (a model independent of pulmonary inflammation).