Stimulation of adenoidal lymphocytes by Alloiococcus otitidis

Otitis media with effusion (OME) is characterized by persistent effusion in the middle ear cavity and by chronic inflammation in the middle ear mucosa . Alloiococcus otitidis, a gram-positive aerobic bacterium, has been isolat ed in middle ear effusion, and by means of sensitive polymerase chain react ion detection assays it has been detected in as many as 20% of middle ear a spirates of patients with OME. Because A otitidis may freely interact with leukocytes in the middle ear effusion, it may potentially modulate the infl ammatory reaction in OME. To study the nature of these interactions, we app lied an in vitro assay in which killed A otitidis bacteria were incubated w ith peripheral blood and adenoidal mononuclear cells. The expression of the proliferation-associated surface marker CD69 was then measured in B lympho cytes and in CD4+ helper and CD8+ cytotoxic-suppressor T lymphocytes by mea ns of multicolor flow cytometry. Alloiococcus otitidis induced the expressi on of CD69 in both peripheral blood and adenoidal T and B cells. Among the T cells, the cytotoxic-suppressor T lymphocytes were preferentially activat ed. It was also tested whether A otitidis would have an effect in another c ytotoxic and immunoregulatory system, namely, the induction of natural kill er cell activity in peripheral blood mononuclear cells. However, the effect was minimal compared with that of Salmonella minnesota or Staphylococcus a ureus. The results show that A otitidis has a unique immunostimulatory capa city in vitro that is mainly confined to CD8+ T lymphocytes.