The relationship between virus infections and increased asthma flares in childhood is incompletely understood. It is now generally accepted that the predominant immune response in atopic asthma is mediated by T cells of the helper subtype (Th2). The following findings are important to note in the context of virus infections and asthmatic exacerbations in children: 1) An early pattern of transient Th2 response occurs in all neonates. This early Th2 bias eventually terminates in most individuals but persists in a significant fraction through adulthood. 2) Wheezing children over 2 years of age frequently have a combination of allergen- specific IgE (a Th2 response) and culture-proven virus infection. 3) In experimental animals, interleukin-4 (IL-4), a Th2-cell-derived cytokine, can convert cytotoxic CD8+T cells into non-toxic Th2-cytokine (IL-5) producing CD8+ T cells. We have recently established that the transcription factor GATA-3 plays a determinative role in Th2-specific gene expression. Also, in collaborative studies with us, Dr. Q. Hamid's group has demonstrated a significant increase in expression of GATA-3 mRNA colocalizing with IL-5 message in human asthmatic bronchoalveolar lavage (BAL) cells and biopsies compared to controls. Taken together, these observations lead us to hypothesize that: a) Viruses cause exacerbations of asthma by augmenting pre-existing Th2 responses through an increase in GATA-3 gene expression. b) Virus-induced increase in expression of the eosinophilic chemoattractant RANTES, which has been shown to activate T cells to trigger IL-5 production, also contributes to increased asthma flares during virus infections. To address this hypothesis we will:
Aim I. Investigate the expression of GATA-3, T cell cytokine and RANTES mRNA in purified peripheral blood T cells of children by quantitative RT-PCR techniques.
Aim II. Determine the consequence of T cell-specific expression of a dominant-negative mutant of GATA-3 on airway inflammation in mice using a doxycycline (dox)-inducible transgenic system recently established in our laboratory. These studies will determine whether inhibition of GATA-3 activity alone can abrogate Th2-like responses in vivo.
Aim III. Determine the consequence of lung-specific inducible RANTES overexpression on T cell activation in vivo in transgenic mice. The effect of RANTES overexpression on GATA-3 and IL-5 gene expression will be investigated in T cells isolated from BAL cells and lung draining lymph nodes.
