Role of bacterial capsule in local and systemic inflammatory responses of mice during pulmonary infection with Klebsiella pneumoniae

The role of bacterial capsule in inflammatory responses in experimentally i nduced pneumonia caused by Klebsiella pneumoniae was evaluated by comparing the host immunological responses in mice infected with capsulate strain DT -S and non-capsulate mutant strain DT-X, Anaesthetised ICR mice were infect ed intranasally with inocula of strain DT-S or DT-X, Mice infected with str ain DT-X survived significantly Longer than those inoculated with strain DT -S, Viable bacterial counts in lungs and blood increased rapidly in mice in fected with strain DT-S, in contrast to the gradual decrease in their densi ty in lungs and intermittent bacteraemia in mice infected with strain DT-X, The number of broncho-alveolar lavage (BAL) cells in mice infected with st rain DT-X at 24 h after inoculation was significantly higher than in those infected with strain DT-S, In the early stages of infection, the levels of tumour necrosis factor-a and interleukin-6 in BAL fluid of mice infected wi th strain DT-X were significantly higher than those of mice infected with s train DT-S, In contrast, in the tate stage of infection, the levels of thes e cytokines in serum of mice infected with strain DT-S were significantly h igher than in mice infected with strain DT-X, These results suggest that K, pneumoniae capsule may suppress the host immunological responses, thus all owing the bacteria to grow, causing pneumonia, septicaemia and death.