Resistance to Klebsiella pneumoniae and the importance of two bacterial antigens.

The resistance of mice to a lethal infection with Klebsiella pneumoniae, type I, was investigated. Antibody of both IgG and IgM class produced good protection when given with an intra-nasal inoculum of the organism. While antibody directed against capsular antigens was highly protective, so too was antibody directed against a second, non-capsular and heat-labile antigen. This antigen does not appear to be related to either the K or O antigens of Klebsiella and is present in several strains of Klebsiella. It is suggested that this antigen may play a role in determining resistance to this organism by humans.