Mechanisms of recurrent bacteria AOM in children under scrutiny

By Joanna Lyford, Senior medwireNews Reporter

The immune response in young children with bacterial acute otitis media (AOM) differs between individuals who are prone to such infection and those who are not, US researchers have shown.

Their finding offers new insights into the different capacities of children to respond to nasopharyngeal colonisation and middle ear infections, say Michael Pichichero and David Verhoeven, from Rochester General Hospital in New York.

Streptococcus pneumoniae and Haemophilus influenzae frequently colonise the nasopharynx mucosa of infants and reflux through the Eustachian tubes to cause AOM. Children can be classified as prone to such infection, typically experiencing three to four middle ear infections per year, or non-prone, with few or no such infections.

In this study, Pichichero and Verhoeven assessed the immune response in three compartments of the body – nasopharynx, middle ear and systemic peripheral blood – of 16 AOM-prone children with a current episode and eight non-prone children without AOM or upper respiratory infection. All children were aged approximately 9 to 18 months.Writing in Clinical & Experimental Immunology, the authors reveal that AOM-prone children had lower levels of interferon (IFN)-γ and interleukin (IL)-2 from pathogen-specific memory CD4 T-cells in their peripheral blood than non-prone children. This same was true for plasma.

In the nasal mucosa, IL-2 expression was higher in infection-prone than non-prone children whereas expression levels of IFN-γ and IL-17a were similar in the two groups. Conversely, levels of cytokines responsible for T-cell expansion and survival such as insulin-like binding protein 4 and IL-7 were lower in AOM-prone versus non-prone children.

Analysis of fluid taken from the middle ear indicated that, as in the nasal mucosa, IFN-γ and IL-17a transcript levels were similar in the two groups of children whereas levels of IL-2 responses were lower in non-prone than AOM-prone children.

Taken together, the findings suggest that cytokine levels in the middle ear are more similar to those of the nasal mucosa than peripheral blood, “suggesting that proximal mucosal sites may better predict the quality of the middle ear response than peripheral blood”, write Pichichero and Verhoeven.

They conclude: “These data suggest a divergence in potential protection from activation induced apoptosis could exist in infection prone and non-prone children. Future studies will examine cytokine mechanisms mediating the expansion and/or survival of T-cells in both populations with respect to lower antigen specific CD4 T-cells.”

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