Primary epithelial cells displayed a higher basal level of transcription of genes for a number of proinflammatory cytokines (IL1α, IL1β, TNFα, CSF, IP10 and CCL5), compared to HeLa cells, with the notable exception of IL6. Infection with C. trachomatis serovar L2 induced expression of several pro-inflammatory cytokines, including IL6, in both HeLa and primary epithelial cells, and the response was stronger in primary cells (Fig. 5a). Here, TNF is linked to infection.