Reaction to intradermally applied phytohaemagglutinin in asthma patients in relation to corticosteroid therapy.

Phytohaemagglutinin (PHA) skin test (diameter of induration 24 h following intradermal injection of 1.0 microgram purified PHA) was carried out on 23 patients with exacerbated atopic asthma and 28 patients with exacerbated non-atopic asthma. Preselected adult patients had either not previously been treated with systemic corticosteroids or steroid therapy had been suspended for at least 3 months. Nearly all non-atopic asthma patients and patients with atopic asthma previously treated with corticosteroids showed increased reactions to PHA. Patients with atopic asthma not earlier treated with corticosteroids demonstrated normal responses. None of the asthmatics showed a negative PHA reaction. Administration of single depot doses of corticosteroids produced decreased reactivity to PHA in nearly all patients. These results suggest that neither atopic nor non-atopic asthma is in itself associated with impaired PHA skin reactivity but that changes in this reactivity are largely due to the corticosteroid therapy administered to these patients. In relation to PHA reactivity certain effects of this therapy may persist for as long as 3 months after its cessation.