Evidence obtained by others who used direct immunofluorescence staining to demonstrate serological differences among strains of
Legionnaires disease bacterium prompted this study of parameters influencing the ability of the indirect immunofluorescence test to detect human
antibodies to
Legionnaires disease bacterium. A total of 25
Legionnaires disease bacterium strains, representing four serogroups, were used as immunofluorescence
antigens to test selected human sera. The use of
diethyl ether in preparing the
antigens was discontinued when it was found that titers against
ether-killed group 2 (Togus 1-like)
antigens were impossible to determine. Instead, heat-killed
suspensions of
Legionnaires disease bacterium in 0.5% buffered normal chicken yolk sac were used to show the serogroup diversity of the strains and the serogroup specificity of the antibody response of some, but not all, patients with serological evidence of
Legionnaires disease. These studies suggest that multiple
antigens should be used in serological tests for
Legionnaires disease. Furthermore, the fact that some sera contain
antibodies that bind equally well to strains of all four serogroups implies that demonstration of a fourfold increase in titer of paired sera when tested with a single
antigen should not be interpreted as evidence of
infection with a strain of the same serogroup.