Second, the chlamydial species and the route of infection determine the type of immune cell that plays a role: In a mouse lung infection model, C. pneumoniae infection is more likely to induce NKT cells to produce IFN-γ, while C. muridarum infection is more likely to induce NKT cells to secrete IL-4, which directly affects the differentiation direction of downstream T cell subsets. This evidence concerns the gene IL4 and infection.