Comparison of specific immunoglobulin G, M and agglutinating antibodies against Legionella pneumophila.

Sera from 25 patients showing a 4-fold or greater rise in polyvalent IFA titer against Legionella pneumophila were examined for the presence of agglutinating antibodies and the titers of specific IgG and IgM immunoglobulins. Agglutinating antibodies were detected in 20 patients (80%) at titers paralleling and amounts of specific IgM present. In sera from the remaining 5 patients (20%), agglutinating antibodies and specific IgM were absent. In this study the class of antibody produced following infection with L. Pneumophila varied from patient to patient. Specific IgM or IgG only was produced or both classes of immunoglobulin appeared concurrently. IFA, using a polyvalent antihuman conjugate, detected both IgG and IgM but cross reactions among the L. pneumophila serogroups occurred in sera from 40.5% of the patients we examined. Tube agglutination measured mainly specific IgM and no cross reactions were evident with this technique. The value of a rapid tube agglutination test as an adjunct to IFA in the serodiagnosis of legionellosis was illustrated in this study.