Effect of interleukin-16-blocking peptide on parameters of allergic asthma in a murine model

Abstract

In this study, we examined whether peptides based on the hydrophilic Cluster of Differentiation (CD) 4-binding part of the amino acid sequence of human interleukin-16 can block interleukin-16-induced chemotaxis of murine lymphocytes in vitro. Peptide 3 was capable of inhibiting interleukin-16-induced chemotaxis of murine splenocytes in vitro. Next, we compared the effects of intra-airway administration of peptide 3 with those of antibodies to interleukin-16 on antigen-induced features in a murine model of allergic asthma. Intra-airway administration of peptide 3 largely inhibited the development of antigen-induced airway hyperresponsiveness while airway eosinophilia was not affected. Similar effects were observed after intranasal application of antibodies to interleukin-16. These results indicate that treatment with peptide 3 causes the same effects as do antibodies to interleukin-16, possibly via the inhibition of interaction between interleukin-16 and its receptor CD4. Therefore, peptide 3 could be useful as a lead compound in attempting to limit airway hyperresponsiveness via binding to CD4.

Introduction

Human allergic asthma is characterised by airway hyperresponsiveness and infiltration of lymphocytes and eosinophils in the lungs (Corrigan and Kay, 1992). There is increasing evidence that CD4⁺ T cells play a crucial role in orchestrating these different phenomena by producing Th2-type cytokines, including interleukin-4 and interleukin-5 Corrigan and Kay, 1992, Virchow et al., 1996.

Besides interleukin-4 and interleukin-5, many other cytokines have been associated with the pathology of asthma, one of them being interleukin-16 (Center et al., 1996). Interleukin-16 has been demonstrated to use the CD4 molecule as its receptor. Upon binding and cross-linking of CD4 molecules, several second messengers, including p56lck and protein kinase C, are activated Haughn et al., 1992, Ryan et al., 1995, Racioppi et al., 1996. Furthermore, interleukin-16 can evoke different functional responses in CD4⁺ cells. One of the most extensively described actions of CD4 cross-linking by interleukin-16 is the induction of chemotaxis in vitro (Center and Cruikshank, 1982). It has been demonstrated that interleukin-16 can induce such responses in various CD4⁺ cells, including eosinophils, monocytes and T helper cells Center et al., 1995, Center et al., 1996. Other biological effects of interleukin-16 include induction of interleukin-2R expression and up-regulation of MHC-II expression in human lymphocytes Center et al., 1995, Center et al., 1996.

Both CD4⁺ and CD8⁺ T cells constitutively express messenger RNA for interleukin-16 and the biologically active protein is secreted from CD8⁺ T cells after stimulation with either histamine or 5-hydroxytryptamine (5-HT) Laberge et al., 1995, Laberge et al., 1996. Furthermore, CD4⁺ T cells release interleukin-16 after mitogen, antigen or anti-CD3 stimulation (Center et al., 1996). Bioactive interleukin-16 can also be produced by eosinophils, mast cells and epithelial cells Bellini et al., 1993, Lim et al., 1996, Rumsaeng et al., 1997. These data suggest that interleukin-16 may be involved in the pathophysiology of asthma. Indeed, in patients with allergic asthma as well as in a murine model of allergic asthma, there is interleukin-16 expression in epithelial cells and bioactive interleukin-16 was found in bronchoalveolar lavage fluid after antigen challenge Laberge et al., 1997, Hessel et al., 1998. Interestingly, inhibition of endogenous interleukin-16 by intraperitoneal administration of antibodies to interleukin-16 has been demonstrated to partially decrease airway hyperresponsiveness but not to affect the number of eosinophils in bronchoalveolar lavage fluid in a murine model of allergic asthma (Hessel et al., 1998).

In a previous study, Keane et al. (1998) demonstrated that peptide 3, which is based on the predicted amino acid sequence of one of the hydrophilic C-terminal regions of interleukin-16, is capable of partially inhibiting recombinant human interleukin-16-induced chemotaxis of peripheral blood mononuclear cells. They also demonstrated that peptide 3 could displace binding of antibodies (OKT4) to CD4 molecules. These data suggest that the C-terminal hydrophilic domain of interleukin-16 is involved in binding to CD4 and is critical for induction of chemotaxis in CD4⁺ cells (Hessel et al., 1998). Additionally, these data suggest that the peptide might inhibit interleukin-16-induced activity by binding to CD4 molecules, thereby preventing cross-linking of CD4 molecules by interleukin-16. Finally, sequence homology of murine and human interleukin-16 is over 80% and cross-specificity is nearly 100% since identical effects were observed on migration of human or murine CD4⁺ T lymphocytes induced by either recombinant human or recombinant murine interleukin-16 and this chemoattracting activity could be blocked by anti-human interleukin-16 mAb (clone 14.1, Keane et al., 1998).

In the present study, we examined the effect of various peptides based on the predicted amino acid sequence of interleukin-16 on recombinant human interleukin-16-induced chemotaxis of lymphocytes in vitro. Next, we examined the effects of intranasal administration of these peptides on airway hyperresponsiveness and eosinophilia in a murine model of asthma. In addition, we compared the effects of local administration of these peptides with those of administration of antibodies to interleukin-16 on the same parameters.