Immunity against Francisella tularensis in northern Finland.

Immunity against Francisella tularensis in northern Finland was studied by antibody determination and by the lymphocyte blast transformation test previously shown to reliably demonstrate immunity to tularemia. Seven out of 1072 (0.7%) Red Cross volunteer blood donors from the rural areas around Oulu had agglutinating antibodies with a titre of 80 or higher, and 5 (0.5%) also had cell-mediated reactivity against F. tularensis. None of them was aware of ever having had tularemia, and only 1 recollected symptoms of tularemia-like illness 15 yr earlier. A high proportion of persons with low titres of antibodies to F. tularensis also had antibodies to Yersinia enterocolitica suggesting that the low titres of antibodies to F. tularensis also had antibodies to Yersinia enterocolitica suggesting that the low titres are unspecific; none of the subjects with such low titres had a positive blast transformation test.