Expression of both TLR4 and TLR21, but not TLR2, is readily increased (6 h post infection) in cecal tissues in response to C. jejuni inoculation in 1-day-old birds, whereas in 2- and 4-week-old broiler chicks this is accompanied, however, by only a limited cytokine gene expression (43). This evidence concerns the gene TLR4 and infection.