Development of Long-Term Specific Cellular Immunity after Acute Blastomyces dermatitidis Infection: Assessments following a Large Point-Source Outbreak in Wisconsin

Ninety-fivepersons exposed to a point-source of Blastomyces dermatitidis</it> in Wisconsinin 1984 were evaluated 3 months after exposure for the development of specific cellular immunity, and the 48 infected persons were again evaluated 7 and 21 months after exposure. The immune response was assessed by an assay of [3H]thymidine uptake by lymphocytes proliferating in responseto stimulation with Blastomyces alkali</it>- and water-soluble antigen (B-ASWS) or blastomycin and byskin testingwith blastomycin. At3 months, 36(84%)of43 patients demonstrated a proliferative response to B-ASWS (mean value of experimental [E) - control [C) counts, 16,852 ± 2664, and of E/C, 42.2 ± 5.3). None ofthe patients demonstrated a proliferative response to blastomycin, and only 19(41%) of 45 patients tested had a positive blastomycin skin test. By 21 months, 47 (98%) of the 48 patients demonstrated a proliferative response to B-ASWS on at least one testing date. Of those initially positive, 82% had a persistently positive proliferative response at 21 months; mean E - C and E/C values were comparable to those seen at 3 months. None of the 47 uninfected persons demonstrated a proliferative response to B-ASWS: 7 with positive histoplasmin skin tests had a mean E - C value of 1094 ± 432, and the 40 others, a mean value of 1139 ± 212. A proliferative response to B-ASWS in exposed individuals is a reliable marker of specific cellular immunity in blastomycosisand the response persists in most patients for up to at least 2 years.