Passive intranasal monoclonal antibody prophylaxis against murine Pneumocystis carinii pneumonia

Abstract

Passive antibody immunoprophylaxis is one method used to protect patients against infection if they are unable to mount an adequate active immune response. Topical application of antibody may be effective against infections at mucosal sites. Using a SCID mouse model of Pneumocystis carinii pneumonia, we were able to demonstrate protection against an airborne challenge with P. carinii by intranasal administration of antibody. Immunoglobulin M (IgM) monoclonal antibodies to an epitope shared by mouse and human P. carinii organisms reduced organism numbers by more than 99% under the conditions described. An IgG1 switch variant of one of the IgM monoclonal antibodies was also protective. These experiments provide a model for exploring the utility of this approach in protecting at-risk patients from infection with P. carinii.

FIG. 1.

Effect of MAb prophylaxis on the outcome of SCID mice exposed to P. carinii. Mice were treated daily with intranasal MAb as indicated on the horizontal axis while being continuously exposed to P. carinii-infected seed mice. The dots represent the number of P. carinii nuclei in the lungs of each animal in this experiment. The dashed line represents the lower limit of detection of organisms in this experiment.

FIG. 2.

Immunofluorescence analysis of the binding of the indicated MAb to mouse P. carinii. The top-row samples were developed with an anti-mouse IgG secondary antibody (2° Ab), while those in the bottom row were developed with an anti-mouse IgM secondary antibody. MAb 2B5 is an IgG MAb specific for mouse P. carinii, and 5E12 is an IgM MAb which binds to both mouse and human P. carinii. The analysis shows that MAbs 4F11 and 1G4 are of the IgM isotype and that 4F11(G1) is of the IgG isotype.

FIG. 3.

Immunofluorescence analysis of the binding of the indicated MAb to human P. carinii. The top-row samples were developed with an anti-mouse IgG secondary antibody (2° Ab), while those in the bottom row were developed with an anti-mouse IgM secondary antibody. MAb 2B5 is an IgG MAb specific for mouse P. carinii, and 5E12 is an IgM MAb which binds to both mouse and human P. carinii organisms. This analysis confirms the isotypes of the various MAbs and demonstrates that MAbs 1G4, 4F11, and 4F11(G1) bind to human, as well as mouse, P. carinii.

FIG. 4.

Western blot of the binding patterns of IgM MAbs 1G4 and 4F11 and of the IgG1 switch variant of MAb 4F11, 4F11(G1). Lanes 1, 3, and 5 contain homogenized P. carinii-infected mouse lung, while lanes 2, 4, and 6 contain homogenized normal mouse lung. Molecular mass markers are noted in kilodaltons.