Vaccination against Legionella pneumophila: serum antibody correlates with protection induced by heat-killed or acetone-killed cells against intraperitoneal but not aerosol infection in guinea pigs.

An aerosol model of Legionella infection has been established in guinea pigs. Infected animals showed growth of Legionella in their lungs, dissemination of organisms to the spleen, development of pneumonia and fever, and weight loss. Vaccination studies using heat-killed or acetone-killed cells were carried out, and guinea pigs were challenged intraperitoneally or by using the aerosol model of infection. Both vaccines were shown to give moderately high levels of protection against intraperitoneal challenge (28 to 145 50% lethal doses). Protection was found to be dose dependent and correlated with antibody levels as measured by enzyme-linked immunosorbent assay to an outer membrane antigen and by indirect immunofluorescence to heat-killed cells. In contrast, the same vaccination regimens that protected against intraperitoneal challenge failed to protect guinea pigs against aerosol challenge with comparable doses of Legionella, despite the presence of serum antibody. The results are discussed in terms of the possible requirements for immunity to aerosolized Legionella, including secretory immunoglobulin or cell-mediated immunity.

Rapid batch method for the preparation of fluorescein isothiocyanate-conjugated antibody.

A rapid, reproducible, and relatively simple method for the preparation of large quantities of fluorescein isothiocyanate-conjugated antibody is presented. Tagged globulins with fluorochrome-protein ratios of 1 and 2 were eluted from diethylaminoethyl-cellulose in batch form by using sodium phosphate-buffered 0.1 M and 0.2 M saline, respectively. The intensity and specificity of the fluorescence due to this antibody was quite high, as determined by the ability of untagged antibody to block the immunological reactivity of the fluorescent antibody and by the lack of fluorescence of antigenically unrelated material when treated under identical conditions.

Role of the macrophage in natural resistance to salmonellosis in mice.

In vitro, macrophages from normal strain BRVR mice killed Salmonella more quickly than did macrophages from normal strain BSVS mice. Salmonella injected intraperitoneally multiplied more quickly in BSVS mice than in BRVR mice. BRVR macrophages injected intraperitoneally into BSVS mice protected against Salmonella multiplication better than did BSVS macrophages. The populations of peritoneal cells that could be washed from the peritoneal cavity of normal BRVR and BSVS mice were morphologically and numerically identical. In vitro, BSVS macrophages were as efficient as BRVR macrophages in phagocytizing virulent Salmonella. These findings all support the concept that the greater natural resistance of BRVR mice to Salmonella infection may be explained by the greater ability of normal BRVR macrophages to kill ingested Salmonella.