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The processing of phagosomes containing Legionella pneumophila and Escherichia coli were compared in Tetrahymena vorax, a hymenostome ciliated protozoan that prefers lower temperatures. L. pneumophila did not multiply in the ciliate when incubated at 20 to 22°C, but vacuoles containing L. pneumophila were retained in the cells for a substantially longer time than vacuoles with E. coli. Electron micrographs showed no evidence of degradation of L. pneumophila cells through 12 h, while E. coli cells in the process of being digested were observed in vacuoles 75 min after the addition of the bacterium. T. vorax ingested L. pneumophila normally, but by 10 to 15 min, the vacuolar membrane appeared denser than that surrounding nascent or newly formed phagosomes. In older vacuoles, electron-dense particles lined portions of the membrane. Acidification of the phagosomes indicated by the accumulation of neutral red was similar in T. vorax containing L. pneumophila or E. coli. This ciliate could provide a model for the analysis of virulence-associated intracellular events independent of the replication of L. pneumophila.

The development of Brugia pahangi (Nematoda: Filarioidea) was studied in nude (congenitally athymic) mice C3H/HeN (nu/nu) and in their phenotypically normal littermates (nu/+). Nude mice were highly susceptible to this parasite. As in the natural host (the cat), the nematodes' third molt in nude mice occurred at 7 to 10 days. The final molt occurred at about 24 days for male worms and 33 days for female worms. Adult worms were smaller than those from other hosts, such as the cat. After inoculation of various numbers of infective larvae, recoveries of adult worms averaged about 15% of the inoculum. In long-term infections initiated with 100 larvae, about 75% of the worms localized in the heart or lungs. Patent infections were seen as early as day 50 PI. Microfilaremia developed in most nude mice given 100, 50, or 25 infective larvae, but was less frequent in those given only 10. Mean filaremias generally rose during the first 6 mo, but in individuals usually did not exceed 500-600/20 mm3 of blood. As in the Mongolian jird, intraperitoneal inoculations yielded large quantities of worms and microfilariae. Few worms could be recovered from normal mice after day 40, even when large (1,000 larvae) inocula were used. Microfilaremia was not detected in normal mice. Although recoveries of adult worms from some nude females were not as high as those from nude males, neither nude nor normal mice showed consistent evidence of a differential susceptibility based on sex. Given the strong, consistent dichotomy of response to B. pahangi between nude and normal mice, this system may be useful in studies of protective immune responses in filariasis.

SUMMARYPolyoma virus demonstrated a requirement for all of the individual amino acids of Eagle's minimal essential medium; however, arginine deprivation inhibited virus synthesis to the greatest extent. Early recovery of virus synthesis upon addition of arginine to an arginine-deprived infection indicated that arginine deprivation possibly inhibited a late step of virus synthesis. Arginine deprivation inhibited polyoma virus DNA synthesis by 6o%, whereas plaque-forming activity was inhibited approximately 9o % during the same period. Arginine deprivation did not affect the number of cells synthesizing structural antigens; however, the encapsidation of virus DNA, dependent upon the synthesis of all structural proteins necessary for virus maturation, was inhibited approximately 9 ° %. A portion of the particles synthesized in arginine-deprived cultures was susceptible to nuclease digestion suggesting incomplete assembly.