Intra- and inter-species transmission and antigenic difference of Pneumocystis carinii derived from rat and mouse.

Pneumocystis carinii (Pc) derived from nude mice (MPc) and hypercorticonized rats (RPc) was subjected to transmission experiments via intranasal (i.n.) route into athymic nu/nu mice (BALB/c background) and run/rnu rats (Rowett hooded strain) and their euthymic heterozygotes rnu/+ rats. Although all these recipient animals received intensive cortisone treatment, MPc propagated only in nu/nu mice. In contrast, RPc strains from three different sources were transmitted successfully to both rats and mice irrespective of their athymicity. The MPc strain could not be transmitted to the other three rat strains used. When RPc organisms were successively propagated in nu/nu mice they lost their pathogenicity to rats after five passages. An antigenic difference between MPc and RPc was suggested by cross reaction of rabbit-raised antiMPc and antiRPc sera against MPc and RPc organisms. An absorption experiment of the sera with both MPc and RPc revealed cross reactivity as well as specific reactivity. The mouse passaged RPc seemed to change the antigenic characteristic to that of MPc.