IL-8 Released Constitutively by Primary Bronchial Epithelial Cells in Culture Forms an Inactive Complex with Secretory Component

Abstract

The bronchial epithelium is a source of both α and β chemokines and, uniquely, of secretory component (SC), the extracellular ligand-binding domain of the polymeric IgA receptor. Ig superfamily relatives of SC, such as IgG and α2-macroglobulin, bind IL-8. Therefore, we tested the hypothesis that SC binds IL-8, modifying its activity as a neutrophil chemoattractant. Primary bronchial epithelial cells were cultured under conditions to optimize SC synthesis. The chemokines IL-8, epithelial neutrophil-activating peptide-78, growth-related oncogene α, and RANTES were released constitutively by epithelial cells from both normal and asthmatic donors and detected in high m.w. complexes with SC. There were no qualitative differences in the production of SC-chemokine complexes by epithelial cells from normal or asthmatic donors, and in all cases this was the only form of chemokine detected. SC contains 15% N-linked carbohydrate, and complete deglycosylation with peptide N-glycosidase F abolished IL-8 binding. In micro-Boyden chamber assays, no IL-8-dependent neutrophil chemotactic responses to epithelial culture supernatants could be demonstrated. SC dose-dependently (IC50 ∼0.3 nM) inhibited the neutrophil chemotactic response to rIL-8 (10 nM) in micro-Boyden chamber assays and also inhibited IL-8-mediated neutrophil transendothelial migration. SC inhibited the binding of IL-8 to nonspecific binding sites on polycarbonate filters and endothelial cell monolayers, and therefore the formation of haptotactic gradients, without effects on IL-8 binding to specific receptors on neutrophils. The data indicate that in the airways IL-8 may be solubilized and inactivated by binding to SC.

The human ovarian follicular fluid level of interleukin-8 is associated with follicular size and patient age

“…a 2 M has been documented to be a carrier protein of IL-8 in the lung, facilitating the binding of IL-8 to neutrophils in an inflammatory setting (16)(17)(18)(19). The precise function of free and a 2 M-bound IL-8 in the human ovarian follicle remains a topic of further study.…”

“…It is known that in the human airway a 2 M interacts with IL-8 modulating its activity (16)(17)(18)(19); therefore, we probed for the presence of free and a 2 M-bound IL-8. Individual FF samples were fractionated by size exclusion chromatography on Superose 6 column and SMART high-performance liquid chromatography (HPLC) (Pharmacia, Uppsala, Sweden), as previously described (22).…”

“…Studies of the human airway indicate that a 2 -macroglobulin (a 2 M) may be an important mediator of IL-8 action through its binding of the protein (16)(17)(18)(19); however, there are no reports of a 2 M in the human ovary.…”

Immunoglobulin Transport and Immunoglobulin Receptors

“…Free SC has been shown to form a high molecular weight complex with interleukin 8 (IL-8) secreted by primary cultures of human bronchial epithelial cells, inhibiting its activity as a neutrophil chemoattractant (Marshall et al, 2001). Other investigators reported that monomeric and polymeric IgA triggered efficient phagocytosis of heat-killed Neisseria meningitidis by human neutrophils but SIgA did not (Vidarsson et al, 2001).…”

Biological Activities of IgA

“…SIgA interacts with the human secretory leukocyte protease inhibitor and can enhance local defense (Hirano et al, 1999). Interaction of SC with CXCL-8 (interleukin-8, or IL-8) makes the latter inactive in terms of leukocyte recruitment in in vitro migration assays (Marshall et al, 2001).…”