Abr deactivates Ras-related C3
botulinum toxin substrate (Rac), a master molecular switch that positively regulates many immune cell functions, by converting it to its
GDP-bound conformation. In this article, we report that, in the absence of Abr function,
cockroach allergen (CRA)-immunized mice experienced a fatal
asthma attack when challenged with CRA. The
asthma in abr(-/-) mice was characterized by increased pulmonary mucus production, elevated serum
IgE, and leukocyte airway infiltration. Decreased pulmonary compliance was further documented by increased airway resistance upon
methacholine challenge. Peribronchial and bronchoalveolar lavage eosinophils, key cells associated with allergic
asthma, were increased in abr(-/-) mice, but adoptive transfer of this cell type from immunized mice to naive controls, followed by CRA challenge, showed that eosinophils are not primarily responsible for differences in airway resistance between controls and abr-null mutants. CD4(+) T cell numbers in the airways of CRA-challenged abr(-/-) mice also were significantly increased compared with controls, as were the Th2 T cell-secreted
cytokines IL-4 and
IL-5 in total lung. Interestingly, when control and abr(-/-) CD4(+) T cells from CRA-immunized mice were transferred to wild-type animals, airway resistance upon challenge with CRA was significantly higher in mice transplanted with T cells lacking Abr function. CD4(+) T cells from CRA-immunized and challenged abr(-/-) mice contained elevated levels of activated
GTP-bound Rac compared with wild-type controls. Functionally, abr(-/-) CD4(+) T cells from CRA-exposed mice showed significantly enhanced chemotaxis toward CCL21. These results identify Abr-regulated CD4(+) T cell migration as an important component of severe CRA-evoked allergic
asthma in mice.