Position paper Microbial products in allergy prevention and therapy Premise Epidemiological and experimental studies have led to the hypothesis that stimulation of the immune system by certain microbial products may prevent or treat allergic diseases (1–5). There are also bacterial products on the market which have been proposed for treatment of allergic diseases but their clinical efficacy is not well documented, however. The European Academy of Allergology and Clinical Immunology (EAACI) appointed a Task Force to critically evaluate available information on the potential use of microbial products in allergy prevention and therapy and to discuss guidelines for future research. This first position paper is separately assessing the effects of bacterial extracts, probiotics, mycobacteria, oligodesoxynucleotides (ISS-ODN), and lipopolysaccha- ride derived molecules in allergic diseases. The section for each of the listed products is structured to present the alleged rationale that would justify their use against allergy and experimental data supporting it. Then, the outcome of representative clinical trials are summarized with regard to efficacy and safety (Table 1). Finally, conclusions are made regarding their potential role in allergic diseases and the eventual need for further research. Asthisisaverydynamicallyevolvingfield,theEAACI- Task Force will keep monitoring the new developments and will upgrade this position paper at regular intervals. Bacterial extracts Bacterial extracts are made from common pathogenic bacterial species, mostly those involved in upper and lower airway and/or urinary tract infections, with some million bacteria of different species/ml. Some recent studies have used bacterial lysate or bacterial surface layer proteins. While early preparations were adminis- tered subcutaneously, newer ones are given orally. Experimental data Oral bacterial extract enhanced natural killer activity and increased spontaneous and PHA-induced production of TNF-alpha,IL-2andIFN-gamma(6)inperipheralblood mononuclear cells in vitro and the expression of adhesion molecules (LFA-1, MAC-1, ICAM-1) in phagocytes (7). Transcription and synthesis of IL-6 and IL-8 have been observed in human lung fibroblasts cultured in the presence of oral bacterial extracts (8). Bacterial extracts inhibit serum-induced IL-12 expression in peripheral blood lymphocytes (9) and were proposed to interfere with other treatments, such as allergen-specific immuno- therapy (10). Inhumanvolunteers,oralbacterialextractsinducedan increase of IFN-alpha, IgA, and IL-2 concentrations in the bronchoalveolar lavage, increased serum total IgG levels and decreased serum total IgE levels (8). In addition, bacterial lysate induced the appearance in the P. M. Matricardi, B. Bjorksten, S. Bonini, J. Bousquet, R. Djukanovic, S. Dreborg, J. Gereda, H.-J. Malling, T. Popov, E. Raz, H. Renz, A. Wold for the EAACI Task Force 7 Paolo M. Matricardi, MD Asthma and Allergy Research Unit Ospedale Pediatrico Bambino Gesu Research Institute – IRCCS Piazza S. Onofrio, 4 00165 Rome Italy Accepted for publication 23 January 2003 Allergy 2003: 58: 461–471 Printed in UK. All rights reserved Copyright Ó Blackwell Munksgaard 2003 ALLERGY ISSN 0105-4538 461