D-082. Modulation of Dendritic Cell Maturation and Function by the OMP P5 Adhesin of Nontypeable Haemophilus influenzae

L. A. Novotny, S. Partida-Sanchez, L. O. Bakaletz;
The Res. Inst. at Nationwide Children's Hosp. and The Ohio State Univ. Coll. of Med., Columbus, OH.

Dendritic cells (DCs) are the primary antigen presenting cells at mucosal sites and serve to initiate and regulate immune responses via discrimination between pathogens and commensal microflora. Specific bacterial outer membrane proteins, including the OmpA protein family, induce DC maturation, cytokine secretion and migration. Nontypeable Haemophilus influenzae (NTHI) expresses an OmpA protein homologue called OMP P5, an adhesin critical to both nasopharyngeal colonization and pathogenesis of NTHI in experimental models of otitis media. While it is currently unclear how NTHI mediates long-term colonization in the absence of an inflammatory response, it is known that proteins expressed by other bacterial species can suppress immune cell activity. We therefore hypothesized that NTHI OMP P5 could modulate DC maturation and function. Expression of CD80, CD86 and MHC class II was comparable between unstimulated DCs and DCs exposed to a low concentration of 103 CFU NTHI. In contrast, up-regulated expression of each molecule was detected after incubation with 105 or 107 CFU NTHI, which indicated a mature DC phenotype. DCs incubated with an isogenic OMP P5 mutant demonstrated a similar maturation marker profile as DCs incubated with the parent strain, suggesting that NTHI concentration was the primary influence for the observed phenotype relative to DC maturation. Functionally, the mature DCs secreted 2 to 3-times more pro-inflammatory chemokines, including IL-8 and MIP-1α, than DCs stimulated with the lower concentration of NTHI. In contrast, no MIP-1α was detected by DCs incubated with isogenic OMP P5 mutant, regardless of bacterial concentration. Finally, a 7-fold increase in chemotaxis was observed by DCs stimulated with the isogenic OMP P5 mutant, compared to incubation with the parent strain. Collectively, these data demonstrated that DCs differentially responded to both NTHI concentration and expression of OMP P5. Further, they offer evidence for an OMP P5-mediated influence on specific DC functions, which may begin to explain how NTHI exists as both a commensal microorganism, yet under certain conditions, an opportunistic pathogen.
Supported by NIDCD/NIH R01DC03915 & R01005847 to LOB