CROSS REACTIONS TO HISTOPLASMA CAPSULATUM IN MICE

It h shown that a cross reaction occurs in mice infected with a sublethal dose of Histoplasma cap-su/atum. The animals howed similar protection, as to llfe, to a challenge with H. capsulatum as they did to Blastomyces dermasqtidis. Protection measured on tissue response in the surviving ani-mals was recognizable with the homologous, but not with heterologous challenge. Salvin obtained homologous sensitivity and immune reaction in a variety of experimental conditions giving living or dead organisms ofH. capsulatum to mice (Salvin, 1953, 1955 a, b). When 35-day old mice were immunized with acetone-dried cells of B. dermatitidis and challenged six days later with H. capsulatum, no protection was demonstrable (Salvin, 1953). Reversal of this experiment im-munizing with H. capsulatum and challenging with B. dermatitidis failed likewise to produce demonstrable protection. In marked contrast to the lack of cross reaction between the two fungi, Salvin (1955) obtained resistance to Rickettsia typhi in mice previously injected with sub-lethal doses of yeast ceils ofH. capsulatum. Mice infected either with B. dermatitidis or H. capsulatum reacted to intrader-mal injection with a partially purified antigen derived from the yeast phase of H. capsulatum (Salvin & Smith, 1959). Indeed, such cutaneous cross reactions with a "crude " (non-purified) antigen had been obtained earlier (Howell, 1947) in experimental nimals (Furcolow, Schwarz, Hewell, & Grayston, 1953) and in men. Similarly cross reactivity in serologic work in human disease had bee