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An allergen cloned from a Blattella germanica(German cockroach) cDNA library, encoded a 182-amino acid protein of 20,904 Da. This protein, designated B. germanicaallergen 4 (Bla g 4), was expressed as a glutathione S-transferase fusion protein in Escherichia coliand purified by affinity chromatography and high-performance liquid chromatography. The prevalence of serum IgE antibody to recombinant Bla g 4 in 73 cockroach allergic patients with asthma ranged from 40% (antigen binding radioimmunoassay) to 60% (plaque immunoassay). Cockroach allergic patients gave positive intradermal skin tests to recombinant Bla g 4 at concentrations of 10-3-10-5μg/ml, whereas non-allergic controls, or cockroach allergic patients with no detectable serum IgE antibody to Bla g 4, gave negative skin tests to 1 μg/ml. Polymerase chain reaction and Southern analysis identified a 523-base pair DNA encoding Bla g 4 in both B. germanicaand Periplaneta americana(American cockroach). However, Northern analysis showed that mRNA encoding Bla g 4 was transcribed in B. germanicabut not in P. americana, suggesting that allergen expression was species specific. Sequence similarity searches showed that Bla g 4 was a ligand binding protein or calycin and unexpectedly revealed that this family contained several important allergens: β-lactoglobulin, from cow milk, and rat and mouse urinary proteins. Although the overall sequence homology between these proteins was low (∼20%), macromolecular modeling techniques were used to generate two models of the tertiary structure of Bla g 4, based on comparisons with the x-ray crystal coordinates of bilin binding protein and rodent urinary proteins. The results show that members of the calycin protein family can cause IgE antibody responses by inhalation or ingestion and are associated with asthma and food hypersensitivity.

Asthma is a leading cause of hospital admission in children. The majority of children with asthma are sensitized and exposed to inhalant allergens that may contribute to chronic airway inflammation.