Acute Otitis Media (AOM) is the most common infectious disease among children. During AOM, children typically have diminished hearing and this can lead to temporary delayed speech and language development and possibly permanent hearing loss. This project seeks support to continue our prospective, longitudinal clinical and translational studies of AOM (RO1 DC 08671) with a specific focus on defining the adaptive and innate immune response deficits among otitis prone (OP) children to infections caused by nontypeable Haemophilus influenzae (NTHi) and Streptococcus pneumoniae (Spn). To better understand NTHi and Spn pathogenesis and assist in vaccine development we plan to (1) identify specific adaptive immune deficits in OP children; (2) determine independent contributions of mucosal immunity in OP children; (3) understand the role of innate responses to co-infection of respiratory bacteria and viruses; and (4) define the role of differences in the nasopharyngeal (NP) inflammatory response in shaping the mucosal microenvironment to allow for NTHi/ Spn colonization and then infection. Therefore, we will investigate: 1. The mechanisms causing a diminished capacity to generate adaptive immune responses to NTHi and Spn following NP colonization and AOM in OP versus non-OP (NOP) children. We will define mechanisms causing poor T-cell function with respect to immune maturity and examine the capacity to generate memory T-cells, compare the generation and activity of NTHi/Spn specific B-cells, define key intrinsic differences of antigen-presenting cell function and evaluate mucosal immune responses. 2. The contributions of innate immunity that alters the NP microenvironment to favor NTHi and Spn colonization during concurrent viral infections to aid the pathogenesis of AOM. We will determine the level of NP and middle ear up-regulation of NTHi/Spn epithelial adherence receptors during antecedent respiratory viral infections; define the role of pro-inflammatory cytokine mediators induced by respiratory viral infections in modifying resistance to NTHi/Spn colonization; and characterize expression of toll like receptors (TLR) as mediators of innate and adaptive immune response clearance of NTHi/Spn colonization. During our current funding time interval, we have re-defined the OP child phenotype thereby providing new clarity and direction in the study of these children. Further understanding immune defects in OP children, will point the way to rational design of future candidate vaccines. Second, we will establish the key mediators of controlled inflammation in the NP during colonization that promote an effective immune response compared to pathological uncontrolled inflammation that allows disease progression. From that knowledge we can seek to modulate or silence those innate immune response pathways that facilitate disease progression while preserving the necessary innate responses that facilitate protective immunogenicity.