Protective role of liposome incorporated lipopolysaccharide antigen of Klebsiella pneumoniae in a rat model of lobar pneumonia.

In a lobar pneumonia model of Klebsiella pneumoniae, the immunoprotective role of free lipoploysaccharide (LPS) and liposome-incorporated LPS was studied. An alteration in the biological activity of the LPS molecule, in terms of its pyrogenicity and lethal toxicity, was observed on incorporation in the liposome. Compared at equal doses, liposome-incorporated LPS was found to be non-pyrogenic and 10 times less toxic than free LPS. Liposome-incorporated LPS was more effective in providing protection against K. pneumoniae induced lobar pneumonia in rats. The immunological mechanism underlying protection revealed involvement of both nonspecific and specific immune response. Alveolar macrophage activation was observed after 4 and 14 days of treatment with the free and liposome-entrapped forms of LPS, respectively. Specific immunity in terms of plaque-forming cells was seen with both forms of LPS. Delayed type hypersensitivity reaction was observed only with liposome-incorporated LPS. It is concluded that a non-toxic and immunogenic form of K. pneumoniae LPS can be obtained by incorporation of the native preparation into liposomes.