PERSISTING HAEMOPHILUS-INFLUENZAE STRAINS INDUCE LOWER LEVELS OF INTERLEUKIN-6 AND INTERLEUKIN-8 IN H292 LUNG EPITHELIAL-CELLS THAN NONPERSISTING STRAINS

Nonencapsulated Haemophilus influenzae strains isolated from patients with chronic bronchitis can be divided into those that persist in the lower respiratory tract and those that do not, We tested the hypothesi s that persisting and nonpersisting strains differ in the extent to wh ich they activate epithelial cells to produce two potent inflammatory mediators, interleukin (IL)-6 and IL-8. A suspension of 10(7) and 10(8 ) colony forming units (cfu).mL(-1) of H. influenzae, persisting and n onpersisting, induced a dose-and time-dependent production of IL-6 and IL-8 by the human pulmonary mucoepidermoid carcinoma-derived cell lin e H292, but levels of IL-6 were lower after exposure to persisting H. influenzae (p<0.05), IL-8 production showed a similar trend (p<0.02; a nalysis of variance), H. influenzae bacteria that adhered to H292 cell s were equally distributed over persisting and nonpersisting isolates and induced IL-6 and IL-8 levels similar to their nonadhering counterp arts, The difference between persisting and nonpersisting H. influenza e was not due to cytotoxic, antimetabolic or antiproliferative effects on H292 cells, Furthermore, pre-exposure of cells to persisting and n onpersisting isolates did not block subsequent IL-1 beta-induced IL-6 production. We conclude that persisting clinical isolates induce less interleukin-6 and interleukin-8 in H292 cells than nonpersisting isola tes, probably because they excrete lower amounts of a stimulus of H292 cells, The stimulus is heat stable, hydrophilic and nonproteinous and probably not lipopolysaccharide alone. These findings support the sug gestion that some strains of Haemophilus influenzae that persist in th e airways of patients, may do so because they induce only a weak infla mmatory response.