Delayed-type hypersensitivity reaction induced in broilers by killed Staphylococcus aureus

A trial was conducted to determine whether the delayed footpad reaction (DFR) induced by killed Staphylococcus aureus in chickens is a delayed-type hypersensitivity (DTH) reaction. Five criteria were used to assess DTH: 1) DFR with a peak response at 24 to 48 h postchallenge, 2) inhibition of monocyte/macrophage migration, 3) lymphocyte blastogenic response, 4) mononuclear cell infiltration at the challenge site, and 5) passive transfer of DFR by splenic lymphocytes. Broilers were sensitized twice with a s.c. injection in the neck of S. aureus antigen (150 microg/bird) diluted in polyethylene glycol at 3 and 4 wk of age. Controls were s.c. injected with polyethylene glycol. At 6 wk of age, a migration inhibition test was conducted before the birds were challenged intradermally with S. aureus antigen (75 microg/bird) in PBS in the right footpad. The left footpad was injected with PBS. The thickness of the footpad was measured at 0, 4, 24, and 48 h postchallenge to evaluate the DFR. After challenge, blood was collected for the lymphocyte blastogenesis assay. Birds were euthanatized, and both footpads were removed for histology. The spleens were collected aseptically; splenic lymphocytes were injected i.v. into recipient birds. Sensitized birds showed an increase in the DFR (P < 0.02) and blastogenic response (P < 0.01) compared with nonsensitized birds. Delayed footpad reaction reached a maximum response at 24 h postchallenge. The in vitro migration of monocytes/macrophages from sensitized birds was significantly inhibited (P < 0.01). The histological appearance of S. aureus-injected footpads was characterized by dermal edema and perivascular infiltrates of small lymphocytes and macrophages. Birds that received sensitized splenic lymphocytes had a significantly pronounced DFR following challenge with S. aureus when compared with birds that received nonsensitized lymphocytes (P < 0.0001). These results indicated that the DFR can be used as a standard in vivo test for cell-mediated DTH reaction induced by killed S. aureus antigen in chickens.