Lymphocyte blastogenic responses to L. pneumophila in acute Legionellosis.

Thirteen patients with acute Legionellosis were studied. Acute serologic studies obtained within the first two weeks of illness were non-diagnostic in 10 of 13 cases. Lymphocyte blastogenic responses to sonicated L. pneumophila were much higher in patients with acute disease (mean net cpm +/- SEM = 66,786 +/- 15,428) than in subjects without a history of Legionellosis (11,800 +/- 1,760) p less than 0.01. Eleven of the 13 patients with acute Legionellosis had net cpm greater than 17,000. Lymphocytes from six patients with acute non-Legionnaires' pneumonia had mean cpm of 3,769 +/- 909 (p less than 0.01). Blastogenic response to L. pneumophila appears to occur earlier than the production of measurable antibody and may be a useful adjunct to diagnosis.