A ROLE FOR ENDOGENOUS HISTAMINE IN INTERLEUKIN-8-INDUCED NEUTROPHIL INFILTRATION INTO MOUSE AIR-POUCH - INVESTIGATION OF THE MODULATORY ACTION OF SYSTEMIC AND LOCAL DEXAMETHASONE

1 When injected into a 6-day-old mouse air-pouch, human recombinant interleukin-8 (IL-8; 0.03-3 mu g) induced, in a dose-dependent fashion, an accumulation of neutrophils which could be reliably assessed 4 h after the injection. No protein extravasation was measured above the values obtained with the vehicle alone (carboxymethylcellulose, CMC, 0.5% w/v in phosphate-buffered solution, PBS). 2 The IL-8 effect (routinely evaluated at 1 mu g dose) was inhibited neither by local administration of actinomycin D (1 mu g) nor by systemic treatment with indomethacin (1 mg kg(-1), i.v.), BWA4C (5 mg kg(-1), p.o.), methysergide (6 mg kg(-1), i.p.) and RP67580 (2 mg kg(-1), i.p.). 3 Treatment of mice with the H-1 antagonist, mepyramine (1-10 mg kg(-1), i.p.) resulted in a dose-dependent inhibition of the cell accumulation elicited by the chemokine, with a maximal reduction of approximately 50-60%. The mepyramine effect was not due to a non specific reduction of neutrophil function, since treatment with this drug (6 mg kg(-1), i.p.) did not modify the cell infiltration measured in response to a challenge with interleukin-1 beta (20 ng) or with the vehicle CMC to any extent. Moreover, treatment of mice with mepyramine did not modify cell counts in a peripheral blood film with respect to controls, Two other H-1 antagonists, chemically unrelated to mepyramine, diphenhydramine (9 mg kg(-1), i.p.) and triprolidine (0.5 mg kg(-1), i.p.), inhibited IL-8-induced migration to a similar extent (approximate to 50-60%), whereas the H-2 antagonist, ranitidine (5 mg kg(-1), i.p.) was without effect. 4 The concept that endogenous histamine could be involved in the IL-8 effect was strengthened in two ways: (i) addition of histamine (0.2-2 mu g) to a small dose of IL-8 (0.3 mu g) potentiated the cell elicitation induced by the chemokine without having any effect on its own; (ii) IL-8-induced neutrophil accumulation was greatly impaired in animals depleted of mast cell amines by sub-chronic (5 day) treatment with compound 48/80 according to an established protocol. 5 The glucocorticoid dexamethasone (Dex; 1-50 mu g per mouse, i.v., corresponding approximately to 0.03-1.5 mg kg(-1), given i.v. 2 h prior to challenge with IL-8) potently inhibited neutrophil infiltration with an approximate ED(50) of 5 mu g per mouse (approximate to 0.3 mg kg(-1), i.v.). Passive immunisation of mice with a polyclonal sheep serum raised against the steroid-inducible anti-inflammatory protein lipocortin 1 (LC1) abolished the inhibitory action of Dex whereas a control serum was without effect. 6 Local administration of Dex at a dose which was ineffective when given systemically (1 mu g) also reduced neutrophil migration induced by IL-8, either alone or in combination with histamine. This local inhibition (approximate to 50%), also seen with hydrocortisone (30 mu g), was prevented by the concomitant administration of the steroid antagonist RU38486 (10 mu g) indicating the involvement of glucocorticoid receptor in the response. 7 These findings characterize further the mechanisms underlying PMN recruitment induced by IL-8 in vivo, and point to a role for histamine. The anti-inflammatory action of the glucocorticoids, as in some other models, appears to be LC1-dependent when these drugs are given systemically and LC1-independent when the steroids are given locally.