The clinical investigations demonstrated the involvement of IL-10 in chronic otitis media. 97,98 IL-10 was identified in middle ear effusions from children undergoing tympanostomy tube placements and its mean concentration was 569/58.7 pg/ml. 97 It has been assumed that the presence of IL-10 in middle ear effusions might be one of the causes of a lack of clinical features of acute inflammation and could lead to a chronic inflammatory state. Chronic otitis media has been also associated with dysregulated local production of IL-10. 98 Patients with chronic otitis media showed high levels of IL-10 ( /100 pg/ml) produced by sinus lavage cell culture and simultaneously low production of IL-10 by peripheral blood mononuclear cells. Investigations of cytokine profiles in different experimental models of OME showed a rapid appearance of IL-10 in the early stages of acute otitis media 99 Á 103 and that IL-10 in mucosa was produced predominantly by CD4 ' T cells. 104 Streptococcus pneumoniae induced expression of IL-10 mRNA in middle ear mucosa within 1Á/2 days after inoculation. 99, 100 Lipoteichoic acid, one of the components present within the cell wall layer of most Grampositive bacteria, 101 and non-typeable Haemophilus influenzae (NTHi) 102,103 induced the expression of IL-10 mRNA in middle ear mucosa even faster, within 6 h after inoculation. It is interesting to note that the expression of IL-10 mRNA followed the expression of TNF-a and IL-6 mRNAs, 99,100 and sometimes occurred simultaneously with the pro-inflammatory cytokines. 101, 102 Thus, clinical and experimental data about IL-10 in OME lead to the following conclusions: