The objective of this study was to investigate the contribution of the interaction between CD40 and its
ligand (
CD40L) to
antigen-induced airways inflammatory responses. To this end, we used a model involving
ovalbumin (OVA) sensitization followed by OVA
aerosol challenge in
CD40L knockout (KO) mice. OVA-specific
IgE and
IgG1 were detected in the serum of the sensitized control, but not in CD40L-KO mice. After
antigen challenge, sensitized control mice developed airway
inflammation that was primarily eosinophilic. This inflammatory response was dramatically reduced in CD40L-KO mice. In contrast, similar numbers of eosinophils were observed in both the bone marrow and the peripheral blood in the sensitized controls and mutant strains after
antigen challenge. To investigate the mechanisms underlying these findings, we examined levels of the
cytokines IL-5,
IL-4, and
TNFalpha in both bronchoalveolar lavage (BAL) and serum. Similar levels of
IL-5 were detected in BAL and serum of control and CD40L-KO mice; however, negligible levels of
IL-4 in BAL and serum and of
TNFalpha in BAL were detected in CD40L-KO mice when compared with control mice. Furthermore, we demonstrated that endothelial cell expression of
vascular cell adhesion molecule 1 in OVA-sensitized and -challenged CD40L-KO mice was, as detected by immunohistochemistry, markedly decreased compared with that observed in similarly treated control mice. In addition, we locally overexpressed
IL-4 and
TNFalpha by using an adenoviral (Ad)-mediated gene transfer approach.
Intranasal administration of either Ad/
TNFalpha or Ad/IL-4 into OVA-sensitized and -challenged CD40L-KO mice did not reconstitute airway
eosinophilia. However, concurrent administration of Ad/
TNFalpha and Ad/IL-4 upregulated endothelial expression of
vascular cell adhesion molecule 1, and resulted in full reconstitution of the inflammatory response in the airways. Together, these findings demonstrate the importance of the CD40-CD40L costimulatory pathway in the full expression of the inflammatory response in the airways.