RSV infection is associated with the development of otitis media, sinusitis(in children) and bronchitis (in adults) due to NTHI. We have recently shown that RSV infection enhances the adherence of NTHI to type II alveolar epithelial cells (A549) by more than 200%, which is mediated almost exclusively by the bacterial surface fimbriae.

In the present study, the role of NTHI fimbriae on regulation of interleukin (IL)-6 and -8 production by RSV-infected A549 cells was evaluated. Confluent monolayers of A549 cells were infected with purified RSV (MOI=0.1) or control media. After 24 h, the supernants were discarded and wild-type NTHI or its fimbriae-deficient isogenic mutant {NTHI(F-)} were incubated(A549:NTHI=1:100). Four h later, the unattached NTHI were removed by washing, and the cell cultures were then incubated with media containing 10μg/ml of gentamicin (to inhibit NTHI growth) for 16 h. The quantities of IL-6 and IL-8 present in the cell culture supernatants were determined by commercial ELISA kits. All experiments were performed in triplicate.

The results are summarized in the table below. RSV as well as wild-type NTHI and NTHI(F-) by themselves significantly enhanced the production of IL-6 and -8 when compared with control (P<0.05). Both strains of NTHI further augmented the IL-6 and -8 production by RSV-infected cells when compared with RSV or NTHI alone (P<0.05). However, augmentation of the cytokines by NTHI(F-) in both control and RSV-infected uninfected cells was lower than that by wild-type NTHI.

Table 1 No caption available.
Full size table

In summary, the bacterial surface fimbriae mediate the enhanced attachment to as well as augment the production of IL-6 and -8 by RSV-infected respiratory epithelial cells. It is therefore likely that blocking of fimbriae mediated attachment of NTHI by chemotherapeutic agents or fimbriae-specific antibodies may reduce the disease occurence or severity due to NTHI during viral infection.