TNF and infection: One study focused on whether there were cytokines in the joints of 11 ReA patients after infections with Chlamydia, Pseudomonas aeruginosa or Salmonella, and showed that under the stimulation of specific bacteria, mononuclear cells in the synovial fluid secrete a small amount of IFN-γ and TNF-α, while secreting a large amount of IL-10.