1. We investigated the mediators responsible for neutrophil migration induced by
ovalbumin (OVA) in immunized mice and the mechanisms involved in their release. 2. OVA administration promoted dose- and time-dependent neutrophil migration in immunized, but not in non-immunized mice, which was mediated by
leukotriene B(4) (LTB(4)) and tumour
necrosis factor (
TNF)alpha, since it was inhibited by LTB(4) synthesis inhibitor (
MK 886) or by LTB(4) receptor antagonist (
CP 105,696), by
dexamethasone and by antiserum to
TNFalpha (82, 85, 63 and 87%, respectively). Confirming
TNFalpha involvement, OVA challenge in immunized p55
TNF receptor deficient mice (p55(-/-)) did not promote neutrophil migration (control: 2.90 +/- 0.68; p55(-/-): 0.92+/-0.23 x 10(6) neutrophils cavity(-1)). 3. OVA-stimulated peritoneal cells from immunized mice released a
neutrophil chemotactic factor which mimicked, in naive mice, neutrophil migration induced by OVA. 4. Supernatant chemotactic activity is due to
TNFalpha and LTB(4), since its release was inhibited by
MK 886 (93%) and
dexamethasone (90%), and significant amounts of these mediators were detected. 5.
TNFalpha and LTB(4) released by OVA challenge seem to act through a sequential mechanism, since
MK 886 inhibited (88%) neutrophil migration induced by
TNFalpha. Moreover, peritoneal cells stimulated with
TNFalpha released LTB(4). 6. CD(4)(+) T cells are responsible for
TNFalpha release, because the depletion of this subset prevented the release of
TNFalpha (control: 400 +/- 25; immunized: 670 +/- 40; CD(4)(+) depleted: 435 +/- 18 pg ml(-1)). 7. In conclusion, neutrophil migration induced by OVA depends on
TNFalpha released by CD(4)(+) cells, which acts through an LTB(4)-dependent mechanism.