OX40-OX40L Interaction Mediates Basophils To Prime Th2 Responses In Ovalbumin-Induced Allergic Airway Inflammation

Background Asthma is a chronic allergic airway inflammation, in which Th2 immune responses play essential roles. Recently, many studies have demonstrated that basophils play a great role in the induction of Th2 responses in different diseases; the underlying mechanisms are poorly understood. OX40-OX40 ligand(OX40L) interaction has been shown to be involved in the Th subsets differentiation and asthmatic inflammation.Objective To confirm the initiation role of basophils in the early phase of allergic airway inflammation, and further explore the potent molecular mechanisms by which basophils initiate Th2 responses, thus leading to allergic airway inflammation.Methods 1. The kinetics of numbers of basophils, dendritic cells(DCs) and Th2 cells in mediastinal lymph nodes(MLN) and the change of molecular expression on basophils were observed in the early phase of asthma, respectively. 2. Establising the basophil differentiation condition: Bone marrow single cells from mice were cultured with recombinant IL-3 and then were sorted by fluorescence-activated cell sorter(FACS). The kinetics of OX40 L and OX40 expression on basophils were evaluated by flow cytometry. 3. The OX40-OX40 L interaction was blocked by OX40 L blocking antibody(anti-mouse CD252) or OX40~-/- na?ve T cells in the basophil and na?ve T cell co-cultures to investigate Th2 differentiation by flow cytometry. 4. To explore the role of OX40-OX40 L interaction in the early phase of asthma, anti-mouse CD252 was injected via tail vein in the sensitization phase of the OVA-induced asthmatic mice. The pathology of lung, levels of ovalbumin-special immunoglobulin E(OVA-s Ig E) in serum, numbers of eosinophils in bronchial alveolar lavage fluid(BALF) and levels of Th2 cytokines such as IL-4, IL-5 and IL-13 were determined, respectively. 5. To determine whether OX40-OX40 L interaction was involved in the induction of Th2 responses initiated by basophils in asthma, the adoptively transfer of basophils model was used. The Th2 cells in MLN, the pathology of lung, levels of OVA-s Ig E in serum, numbers of eosinophils in BALF and levels of Th2 cytokines such as IL-4, IL-5 and IL-13 were determined, respectively.Results 1. The number of basophils increased significantly, but not DCs in the MLN in the early phase of asthmatic mice. In addition, the peak of basophils was earlier than that of Th2 cells Th2 cells. Among the array of molecules on basophils, the level of OX40 L expression altered most remarkably. 2. Basophils can express OX40 L in the presence of IL-3 plus DNP-OVA and anti-DNP Ig E in vitro. 3. Blockade of OX40-OX40 L interaction inhibited the Th2 cell differentiation primed by basophils in vitro. 4. The levels of serum OVA-s Ig E, numbers of eosinophils and levels of IL-4, IL-5 and IL-13 in BALF decreased, thus alleviating inflammation in lung when OX40-OX40 L interaction was blocked by anti-mouse CD252 in the early phase of asthma. 5. The adoptive transfer of basophils derived from MLN of OVA-immunized mice triggered a robust Th2 response and eosinophilic inflammation in wild-type recipients but largely muted in OX40~-/- recipients and in mice receiving OX40L-blocked basophils.Conclusions 1. Basophils participate in the induction of allergic airway inflammation. 2. Basophils can express OX40 L in an inducible manner in vivo and in vitro. 3. OX40-OX40 L interaction is involved in the Th2 cell differentiation primed by basophils in vitro. 4. Basophils-associated OX40 L participates in initiation of Th2 responses, thus leading to asthmatic inflammation.