Expression of α4-integrins on human neutrophils

Abstract α4 Integrins are important adhesion molecules mediating binding of lymphocytes, monocytes, and eosinophils to multiple cellular and extracellular ligands. Mature neutrophils have been recently suggested to express α4-integrins as well. We studied whether human neutrophils can synthesize α4-integrins upon activation in vitro or in vivo. Two anti-α4 mAbs, but not multiple subclass-matched non-binding controls, reacted with granulocytes in an inducer and time-dependent manner. Nevertheless, staining with Ig subclass-specific second-stage reagents surprisingly revealed that commercial anti-α4 mAbs contain two distinct Igs, the α4-specific IgG1 and an IgG2a of an unknown specificity. We showed that in vitro inductions used by us and others only induce the binding of nonspecific IgG2a from the commercial HP2/1 to activated neutrophils. By reverse-transcriptase polymerase chain reaction, α4 mRNA was not detectable in purified neutrophils. Our results show that α4 integrin protein and mRNA are absent from normal and stimulated human neutrophils.