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The neutrophil‐activating proteins interleukin 8 and β‐thromboglobulin: in vitro and in vivo comparison of NH2‐terminally processed forms

Isolation of the human neutrophil activating protein (NAP) interleukin 8 (IL 8) from leukocytes has revealed that it is structurally related to β‐thromboglobulin (βTG) 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 βTG forms for in vitro and in vivo neutrophil activation. In contrast to IL8, none of the βTG 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 βTG (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 vasodilatator substance low doses (2–20 pmol) of IL8 and the shorter forms of βTG caused granulocyte accumulation and plasma leakage in rabbit skin whereas the longer forms of βTG 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 βTG. It can be concluded that the platelet factor βTG, structurally related to the monokine IL8, can also play a role in neutrophil activation during inflammatory reactions.