Relationship of Histoplasmin Agar-Gel Bands and Complement-Fixation Titers in Histoplasmosis

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Abstract
Wiggins, GeraldineL. (Communicable Disease Center, Atlanta, Ga.),and Joseph H. Schubert. Relationship of histoplasmin agar-gel bands and complement-fixation titers in histoplasmosis. J. Bacteriol.89:589–596. 1965.—Culture filtrates of various strains ofHistoplasma capsulatumwere studied with sera from patients with histoplasmosis, by use of the agar-gel and complement-fixation tests. It was found that the filtrates represented three types: those containing H and M components, those with H only, and those with neither H nor M. The same strain ofH. capsulatumoften produced culture filtrates of more than one type. Complement fixation showed that only the filtrates having both the H and M components were sufficiently sensitive as diagnostic antigens to detect the antibodies in histoplasmosis. H and M fractions prepared by ion-exchange chromatography were found to produce more than one band; therefore, it was concluded that the available fractions were not pure. The formation and identification of bands were affected by the concentration of the antigen and the arrangement of the wells containing the antigen and serum. The optimal concentration of the antigen varied, depending on the position of these reagents. The method found most practical for the identification of bands in unknown sera consisted of selecting the optimal concentration of the components with a box titration, by use of antigen having both the H and M components, placing known positive sera in wells adjacent to the unknown sera, and studying the sera for lines of identity. The M band was usually closest to the antigen well, and the H was nearest the serum well. These bands could be reversed by dilution, adjusting the H antibodies so that they equalled or exceeded the M antibodies. One human serum in which the bands were reversed showed the H bands at a higher serum dilution than that obtained with the M band. Patients with culturally proven histoplasmosis had the M band in their serum regardless of the stage of disease or length of duration; only 4 of 10 patients in the active stage of histoplasmosis also had the H band. The low prevalence of the H band would eliminate it as a diagnostic tool for detecting the active stage of the disease. Other bands obtained with histoplasmin antigen in the sera from proven cases were of no assistance in determining the clinical status of the patient.