INTRODUCTION
Cockroach is a common allergen in urban and under-resourced areas and a significant source of atopic morbidity worldwide, particularly among children and young adults1-3. The German cockroach (CR, Blattella germanica ) is commonly associated with CR allergies in the United States with CR allergens being detected in 85% of homes in low-income urban communities 4. CR allergy has a high prevalence, and has long been established as a strong cause of asthma initiation and progression with early exposure leading to increased CR sensitization, asthma severity, and morbidity 4-8.
Several studies defined CR allergens based on IgE reactivity from sensitized individuals and correlated sensitization prevalence with severity of clinical symptoms 3,9-12. T cells, and in particular type 2 T helper cells, significantly contribute to the development of allergy and asthma 13-15; however, CR-specific T cell responses have been characterized in less detail16-21, and very little information is available particularly for the population most impacted by CR allergies, namely urban and under-resourced children.
In general, allergen-specific T cell responses are often characterized following in vitro expansion steps 17,22-25 to account for their low frequency which may also alter the phenotype of responding T cells 26. We and others previously demonstrated that allergen-specific T cells can be detected ex vivo  using a novel assay strategy with the combination of several T cell epitopes into pools 24,27-29. This technique uses the upregulation of the activation markers such as CD154 (CD40L) as a read-out for T cell reactivity and can be combined with intracellular cytokine staining (ICS) to further identify T cell phenotypes as well as polyfunctionality 24,27,30 and to improve the characterization of CR-specific T cell responses.
Thirteen groups of German CR allergens have been defined based on IgE reactivity and are listed at the official allergen database maintained by the World Health Organization and International Union of Immunological Societies (WHO/IUIS) Allergen Nomenclature Sub-committee (www.allergen.org) 2. As in the case of other allergies (i.e., cat, mite, or mouse24,27,31,32), certain allergens have been described as dominant for CR-specific T cell responses. Those studies however were associated with certain limitations, such as testing a set of candidates derived from predicted epitopes from a more limited set of allergens, reliance on in vitro expansion and re-stimulation steps, and most importantly they only addressed dominance in sensitized adults16-18.
Here we characterized the patterns of T cell responses to 11 cockroach allergens in a cohort of children with CR sensitization and asthma with a median age of 12 years that were enrolled as potential participants in an IT clinical trial (CRITICAL). Before initiation of IT treatment,ex vivo T cell reactivity and the cytokine profile specific for each individual allergen was determined using pools of overlapping peptides spanning the entire protein sequence of the various CR allergens. The basal numbers of regulatory CD4+ T cells (Tregs) was also assessed, and compared with the magnitude of effector T cell responses. Additional correlation analyses were performed to examine the relationship of T cell responses to skin prick test and serological IgE responses 33 as well as to the Composite Asthma Severity Index (CASI) and its components 34.