Influence of the skin-test on blood IFN-γ responses. (A) IFN-γ responses were measured in blood samples from cattle naturally infected with M. bovis around the time of three consecutive SICCT tests (ST1–ST3, n = 15, 13, 23 respectively). Blood samples were tested prior to (shaded bars) and at 3 (solid bars) and 10-days (unshaded bars) following each of three skin-tests. (B) Comparison of the effect of CFT and SICCT tests on blood IFN-γ responses was measured in 8 and 15 cattle respectively. Responses were measured prior to, and 3 and 10 days post skin-test (ST1) and the response in cattle given the CFT and SICCT tests are show as open and closed circles respectively. Where a response at either day 3 or 10 was significantly different from the pre-test response, this is indicated (*p < 0.05). For both panels, data are presented as mean (OD_450 nm) of the PPD-B stimulated response minus the PPD-A response (± standard error).