No abstract

Mechanisms involved in neutrophil accumulation induced by intradermal injection of interleukin‐1 (IL‐1) in the rabbit were investigated using intravenously‐injected 111In‐labelled neutrophils. C5a des Arg, N‐formyl‐methionyl‐leucyl‐phenylalanine (FMLP) and leukotriene B4 (LTB4) were included for comparison. Local inhibition of protein biosynthesis in the skin using actinomycin‐D or cycloheximide blocked 111In‐neutrophil accumulation induced by IL‐1, but not that induced by the other mediators. Actinomycin‐D and cycloheximide had no effect on local plasma protein leakage induced by intradermally‐injected C5a des Arg, or that induced by zymosan. 111In‐neutrophil accumulation induced by zymosan was, however, partially suppressed. A monoclonal antibody, MoAb 60.3, recognising neutrophil surface CD18 antigen, was preincubated with 111In‐neutrophils before intravenous injection. This pretreatment did not affect circulating numbers of radiolabelled cells, but it inhibited their accumulation in response to IL‐1, C5a des Arg and the other mediators. The results suggest that neutrophil accumulation induced by IL‐1, but not the other mediators, requires local protein biosynthesis, probably in the microvascular endothelium. Neutrophil accumulation to IL‐1 and the other mediators appears to require neutrophil surface antigen, CD18. The inflammatory response to zymosan may be mediated by both endogenous C5a des Arg and IL‐1.

Isolation of the human neutrophil activating protein (NAP) interleukin 8 (IL8) from leukocytes has revealed that it is structurally related to beta-thromboglobulin (beta TG) from platelets. Both these proteins occur as natural mixtures of multiple forms, differing from each other by unequal truncation at the NH2 terminus. In this study we have compared IL8 and beta TG forms for in vitro and in vivo neutrophil activation. In contrast to IL8, none of the beta TG forms were found to exert granulocyte chemotactic activity in vitro, as measured in the agarose assay. However, fractions rich in the most extensively processed forms of beta TG (e.g. NAP-2) as well as pure NAP-2 did induce lactoferrin release from granulocytes, whereas fractions containing only the longer forms (e.g. connective tissue-activating peptide III) were inactive. In order to observe this in vitro effect, about 10-fold less IL8 (10 nM) than NAP-2 was required. In the presence of a vasodilator substance low doses (2-20 pmol) of IL8 and the shorter forms of beta TG caused granulocyte accumulation and plasma leakage in rabbit skin whereas the longer forms of beta TG again failed to do so. Finally, granulocytosis induction following i.v. injection was found to occur with NAP-2. At the maximal dose tested (250 pmol), this in vivo effect of NAP-2 was less pronounced than that of IL8. In the case of IL8, NH2-terminal processing did not seem to affect granulocyte stimulatory activity. It should be noted, however, that the extent of processing of IL8 is less than that occurring with beta TG. It can be concluded that the platelet factor beta TG, structurally related to the monokine IL8, can also play a role in neutrophil activation during inflammatory reactions.