Naturally occurring immune response against bacteria commonly involved in upper respiratory tract infections: analysis of the antigen- specific salivary IgA levels Giovanni A. Rossi a , Cristiano Peri b , Maria E. Raynal a , Anna-Carla Defilippi a , Francesco M. Risso a , Guido Schenone c , Eugenio Pallestrini c , Giovanni Melioli b, * a U.O. di Pneumologia, Istituto Scientifico Giannina Gaslini, Largo G. Gaslini 5, 16100 Genoa, Italy b U.O. Laboratorio di Analisi, Istituto Scientifico Giannina Gaslini, Largo G. Gaslini 5, 16100 Genoa, Italy c Dipartimento di Capo e Collo, Azienda Ospedale S. Martino, Genoa, Italy Received 20 September 2002; received in revised form 19 November 2002; accepted 28 November 2002 Abstract Lyophilized bacterial lysates, which actively stimulate the immune response, are widely used as vaccines or ‘biological response modifiers’ in subjects with recurrent bacterial respiratory infections. Since vaccines are indicated in the absence or in the presence of a weak constitutive immune response activity, a better knowledge on the ‘naturally’ occurring antibacterial immune response at the oropharingeal level should be helpful. A study was, therefore, designed to quantify the presence of salivary IgA directed against surface antigens bacteria frequently involved in the pathogenesis of upper respiratory tract infections: Klebsiella pneumoniae (KP), Staphylococcus aureus (SA), Streptococcus pyogenes (SPy), Morraxella catarrhalis (MC), Haemophylus influenzae (HI), and Streptococcus pnumoniae (SPn). In 34 volunteers (21 adults and 13 children), salivary fluid was collected and the presence of microorganism-specific IgA antibodies evaluated by a novel enzyme immuno-assay. In the whole population only 29 and 24% of subjects had IgA directed, respectively, to KP and SA, while the immune-response against other microbes was detectable in a small population ranging from 12 to 15% of all subjects studied. We found higher proportions of individuals with strain specific salivary IgA in the adult than in the pediatric population for all the microorganism evaluated. In addition, in children, the only strain inducing a significant production of specific IgA at oropharingeal level was KP. Interestingly, only ten out of 21 adults and two out 13 children have at least one significantly high antibody titer against one of the bacteria evaluated. Nevertheless, when a group of healthy donors was treated with a polyvalent mechanical bacterial lysate (Ismigen t.), the large majority developed a specific immune-response in the salivary fluid. These results are thus consistent with the good features of the novel enzyme-immunoassay and with a poor frequency of naturally induced specific anti-microbe antibodies in children and in adults despite the presence on recurrent respiratory infections in their clinical history. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Infection; Immunoglobulin; Bacteria 1. Introduction One of the difficult-to-deal problems in medical practice is the management of the patients with persis- tent or recurrent upper respiratory tract infections with or without associated chronic bronchial involvement [1]. Since a significant proportions of these subjects do not have detectable underlying etiologic factors explaining the recurrence of symptoms, this condition is frequently explained as a reflection of a familial or individual susceptibility or as the result of repeated exposure to infectious agents, at home or at school [1] for children and at home or at work for adults [2]. The observation that recurrent respiratory infections may be caused by or associated with secretory IgA deficiencies [3], has suggested as ‘prophylactic approach’ the stimulation of the ‘mucosal’ immune response against microorganisms commonly involved in the * Corresponding author. Tel.:  /39-010-563-6557; fax:  /39-010- 379-7977. E-mail address: giovannimelioli@ospedale-gaslini.ge.it (G. Melioli). Immunology Letters 86 (2003) 85  /91 www.elsevier.com/locate/ 0165-2478/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. doi:10.1016/S0165-2478(02)00290-0