FIG 4.

Distinct cell populations are responsible for inflammation in neonates. (A) Neither CD4⁺ cells nor B cells are required for initiating inflammation in response to Y. enterocolitica infection in neonates. Neonatal wild-type C57BL/6 (wt) (●), μMT (▲), and CD4^−/− (◆) mice were infected orogastrically with 5 × 10⁸ CFU Y. enterocolitica, and the MLN were evaluated for neutrophil recruitment by flow cytometry 24 h postinfection. Open symbols represent uninfected animals. (B) Representative flow cytometry profiles showing efficiency of CD11b⁺ cell depletion. (C) Neonatal MLN cells were depleted of CD11b⁺ cells by MACS separation, and RNA was evaluated for gene expression in the whole fraction (●) and CD11b-depleted (○) fraction 18 h postinfection. The left y axis corresponds to Il6, Il17a, and Il10. The right y axis corresponds to Ifng. Data are expressed relative to the lowest expressor. ns, not significant; *, P ≤ 0.05.