Antibacterial immunity of lower airways: local or localized?

Clearance of bacteria in the bronchoalveolar lavage, the level and functional activity of IgA and changes in the cellular composition of BAL were examined in mice after supralaryngeal immunization and subsequent challenge with Klebsiella pneumoniae. More than 60% of the bacterial inoculum was removed by nonspecific mechanisms within 90 min after inoculation; within the time interval 1.5-3.5 h, clearance was significantly accelerated in locally immunized mice. The enhancement of clearance effectiveness is specific and increases proportionally with the length of immunization (1 less than 2 less than 4 weeks); it is of short duration and towards the end of the 3rd week after immunization, in 73% of immunized animals, the clearance values did not differ from values found in controls. The local immunization did not influence the total level of IgA in BAL, the formation of specific IgA antibody was minimal, in vivo binding of IgA to klebsiella could not be demonstrated. In immunized mice, a significant increase in the numbers of PMN and lymphocytes, as well as an increased activity of phagocytic cell (PMN, MP) was found in BAL. The time interval of 1.5-3.5 h after challenge bounds the space for mechanisms, activated by local immunization in lower airways. The actual participation of individual factors in the accelerated elimination of bacteria from the lumen of airways, remains unclear so far.