Constitutive expression of IL-2Rbeta chain and its effects on IL-2-induced vascular leak syndrome
Introduction
Interleukin-2 (IL-2) exerts a broad spectrum of effects on the immune system and plays a crucial role in regulating both immune activation and homeostasis [1], [2], [3], [4]. Clinical trials using human recombinant interleukin-2, alone or in combination with the adoptive transfer of lymphokine-activated killer cells (LAK), has been shown to result in tumor regression in 25–30% of patients with metastatic melanoma or renal carcinoma [5], [6]. Intermittent IL-2 administration is also used in HIV-infected patients in combination with highly active anti-retroviral therapy (HAART). This association restores sustained, protective levels of CD4+ T lymphocytes [7], [8], [9], [10], [11]. However, the therapeutic use of IL-2 is restricted by its dose-dependent toxicity. Its side effects stem mainly from the development of vascular leak syndrome (VLS). IL-2-induced VLS is characterized by increased vascular permeability and decreased microcirculatory perfusion leading to interstitial edema and multiple organ failure [12], [13].
In a recent paper we addressed the cellular mechanisms involved in IL-2-induced VLS and described a mouse model of IL-2-induced pulmonary VLS. This was used to analyze both the early events (bronchoconstriction and sequestration of polymorphonuclear neutrophils) and the late events (modifications in the cell and protein contents of bronchoalveolar lavages, followed by edema) that characterize this lung injury [14]. Early/acute events were observed after one IL-2 injection whereas late/chronic events were measured after four IL-2 injections. By comparing the results obtained between C57BL/6 and Recombinase-activating gene 2 −/− mice, we showed that B, T and NKT lymphocytes are not required for IL-2-induced pulmonary VLS. By contrast, results obtained with double KO mice (Recombinase-activating gene 2 −/− //IL-15 −/−) demonstrated that NK cells are involved in both the early and late phases of the syndrome. Furthermore, granulocyte depletion was entirely effective in protecting mice from the late events of IL-2-induced pulmonary VLS, thereby demonstrating that NK lymphocytes and PMN are both critical for IL-2-induced pulmonary VLS late events [14].
IL-2 responsiveness is in part controlled by the expression of interleukin-2 receptors (IL-2R). In humans, two types of functional receptor have been described. The high affinity receptor is made of three chains (hIL-2Ralpha, hIL-2Rbeta and hIL-2Rgammac) [15], [16], [17], [18], [19], [20], [21]. Intermediate affinity IL-2R is composed of the association of hIL-2Rbeta and hIL-2Rgammac chains, which are selectively expressed by NK cells and monocytes, respectively [22]. Mice lack intermediate-affinity IL-2R and IL-2 responsiveness in these animals is entirely dependent on IL-2Ralpha expression [23], [24]. Therefore, the IL-2R system is different in humans and mice and the animal model may not be the most appropriate for studying the in vivo effects of human IL-2.
Here we further investigate the mechanisms involved in IL-2-induced VLS and used previously characterized human IL-2Rbeta transgenic mice for our experiments [25]. In these animals, the H-2k promoter supports constitutive expression of human IL-2Rbeta chain. We have verified that this chain is expressed by all cells of the immune system and that it did not modify the pattern of expression of mouse IL-2R chains [26]. The expression of human IL-2Rbeta chain in the presence of endogenously expressed murine IL-2Rgammac chain is sufficient to obtain a functional intermediate-affinity IL-2R [23], [27], [28]. These animals were used to analyze the role of the IL-2R complex in the early and late events that characterize the toxic pulmonary effects of human IL-2. Based on our results we also suggest that the human IL-2Rbeta transgenic mouse model may be useful for future studies aimed at evaluating the therapeutic index of human IL-2 or human IL-2 mimetics.
Section snippets
Inducing the early and late phases of vascular leak syndrome
Mice were injected i.v. with 10 μg of IL-2 (180,000 IU Aldesleukin, Chiron B.V., Amsterdam). Control mice were injected i.v. with NaCl (0.9%). Acute responses were evaluated 2 h after the first IL-2 injection. Late responses were measured after four daily i.v. injections and the different biological parameters were analyzed at the times indicated.
Mice were 6–9-week-old males. Wild type C57BL/6 mice were purchased from “CNRS CDTA” (Orléans, France). Human IL-2Rbeta transgenic animals on C57BL/6
The early events of IL-2-induced VLS are amplified in human IL-2Rbeta transgenic mice
The pathophysiological effects of a single IL-2 injection were first assessed by measuring bronchoconstrictive response to aerosolized metacholine. Whole body plethysmography was used to measure airway resistance to 100 mM metacholine. The results obtained with C57BL/6 mice and human IL-2Rbeta transgenic animals of the same genetic background were compared. As shown in Fig. 1, the bronchoconstrictive response of C57BL/6 mice to metacholine was significant 2 h after the first i.v. injection (AUC
Discussion
Given that the therapeutic use of IL-2 is restricted by its side effects, we considered it critical to unravel the mechanisms behind IL-2-induced VLS. We recently described a mouse model used to investigate the cellular mechanisms participating in IL-2-induced pulmonary VLS. We described the preponderant role played by NK cells in early events and the involvement of both NK and PMN cells in late-phase VLS [14]. Here, in this paper we begin to study the role played by IL-2R in IL-2-induced
Acknowledgements
We would like to thank Professor Tasuku Honjo (Department of Medical Chemistry, Faculty of Medicine, Kyoto University, Kyoto, Japan) for generously providing the human IL-2Rbeta transgenic mice and for his continuous support. The authors would also like to thank Laurence Motreff and Marianne Nahori for their technical assistance. The work was supported by Grants from Agence Nationale de Recherche sur le SIDA (ANRS) and Institut National de la Santé et de la Recherche Médicale (INSERM).
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Eric Assier and Valérie Jullien made equal contributions to this paper.