Mechanisms of asthma and allergic inflammation
Cyclophosphamide augments inflammation by reducing immunosuppression in a mouse model of allergic airway disease

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Background

Allergic asthma is a TH2 cell–driven immunological disease, characterized by eosinophilic inflammation. The cytotoxic agent cyclophosphamide paradoxically augments several immune responses.

Objective

We studied the proposal that cyclophosphamide may aggravate airway inflammation in allergic mice, and these features might result from the loss of regulatory T cells.

Methods

BALB/c mice were immunized with ovalbumin on days 0 and 14 and challenged with aerosolized ovalbumin from days 21 to 27. Some mice also received cyclophosphamide on days –2 and 12.

Results

In the lungs of cyclophosphamide-treated animals, pronounced worsening of inflammatory features was noted, including increased eosinophil infiltration, epithelial thickness, mucus occlusion, and eosinophil numbers in bronchoalveolar lavage fluid. There was also increased total and ovalbumin-specific serum IgE, increased IL-4 and IL-5 secretion by peritracheal lymph node cells, and reduced lung mRNA expression of IL-10 and TGF-β in animals treated with cyclophosphamide. The expression of FoxP3, a marker of regulatory T cells, was significantly reduced in lymphoid organs after the second injection of cyclophosphamide, and in the lung tissue after allergen challenge in cyclophosphamide-treated mice. Lung IL-10+CD4+ T cells and cytotoxic T lymphocyte–associated antigen 4+CD4+ T cells were reduced after allergen challenge in cyclophosphamide-treated mice.

Conclusion

Cyclophosphamide worsened features of allergic pulmonary inflammation in this model, in association with increased production of IgE and TH2 cytokines. The reduced expression of FoxP3 and immunosuppressive cytokines by cyclophosphamide is consistent with the possibility that toxicity to regulatory T cells may contribute to the increased inflammation.

Section snippets

Animals

Female BALB/c mice, 6-8 weeks old, were obtained from Animal Resources Centre (Perth, Australia). All animals were housed in pathogen-free conditions at the Garvan Institute of Medical Research. All experiments were approved by the Garvan/St Vincent's Animal Experimentation Ethics Committee and conducted according to the animal welfare guidelines of the National Health and Medical Research Control of Australia.

Induction of asthma and administration of cyclophosphamide

Mice were immunized and boosted by intraperitoneal injection of 100 μg ovalbumin

Cyclophosphamide exacerbated lung inflammation

Mice were immunized twice with ovalbumin and challenged 4 times by inhalation of aerosolized ovalbumin. Lung histology was assessed 24 hours after the last challenge. In these mice (ovalbumin group), high-power examination revealed significant cellular infiltration including numerous eosinophils in the perivascular and peribronchial areas (Fig 1, A). Sections of ovalbumin-immunized and challenged mice given 2 injections of cyclophosphamide (CY/OVA group) showed a much more pronounced cellular

Discussion

We have demonstrated that administration of cyclophosphamide was followed by increased airway allergic inflammation in a mouse model. Features increased by cyclophosphamide included eosinophilia in the lung tissue (Fig 1) and BAL fluid (Fig 2), serum IgE, and production of TH2 effector cytokines, IL-4 and IL-5 (Fig 3). The features augmented by cyclophosphamide are all consistent with a TH2 response. Cyclophosphamide is well known to augment TH1-mediated autoimmune diseases and other TH

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  • Cited by (0)

    Supported by the Cooperative Research Center for Asthma and by Infrastructure Grants from the New South Wales State Health Department. Dr Su is funded by an Endeavour International Postgraduate Research Scholarship from the Faculty of Medicine, University of New South Wales.

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