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SummaryThe lpr gene induces in mice, accumulation of large numbers of CD4 -CD8 -(double negative [DN]) T lymphocytes which bear adhesion molecules not characteristic of normal resting T cells . These cells fail to acquire interleukin 2 (IL-2) receptors, produce IL-2, and proliferate when activated with mitogens or monoclonal antibodies (mAbs) against the T cell receptor (TCR) . Because of these poor functions in vitro, the nature and significance ofDN T cells in the autoimmune disease process is not clear. In the current study, we describe a surprising finding that mAbs against CD3-TCR-tx/(3 complex can strongly trigger the lytic activity of the DN T cells to induce redirected lysis of Fc receptor-positive targets . Similar redirected lysis was also inducible using mAbs against CD44 and gp90Mt :L-14, molecules involved in the binding of lymphocytes to endothelial cells. The spontaneous cytotoxic potential ofthe DN T cells was further corroborated by demonstrating that the lpr DN T cells constitutively transcribed perforin gene but failed to express granzyme A. The current study suggests that DN T cells are capable of mediating lysis ofautologous cells bearing the specific ligands for adhesion molecules involved in the signaling of cytotoxicity. These findings provide a novel insight into the functional significance of DN T cells in lpr mice and their potential role in the pathogenesis of autoimmune disease.

SYNOPSIS. A Tritrichomonas foetus‐likt flagellate was found in the stomach, small intestine, and cecum as well as in the nasal cavity of pigs. Xo appreciable differences in morphology or response to cultivation could be found among the trichomonads from the different sites; therefore, it is considered that they.belong to a single species, Tritrichomonas suis (Gruby & Delafond). a description of which is given. This organism could be grown indefinitely in various media, and, after a short period of cultivation, it was the only species surviving in cultures that originated from cecal samples containing 2 or 3 species. T. suis was found in the nasal cavity in 55 of 100 pigs, in the stomach in 41 (8.0%) of 512, in the small intestine in 3 of 100. and in the cecum in 215 (43.370) of 496. A T. batrachorum‐type trichomonad, herein described as Tritrichomonas rotunda n. sp., was found in the cecum in 52 (10.5%) of 496 pigs. This species is typically broadly pyriform or rotund (average length 8.95 ± 0.83 ii, range, 6.83‐11.4), with 3 equal or subequal anterior flagella slightly longer than the body, a relatively low undulating membrane extending y2 to 2/1 of the length of the body, and a posterior free flagellum usually a little shorter than the body. The narrow axostyle, expanded anteriorly into a curved capitulum closely associated with the large, spherical, anteriorly located nucleus, projects from the posterior surface of the flagellate for a distance which equals about 2/3 half of the body length. The parabasal apparatus is biramus. This species could be maintained only temporarily in media not containing extracts of cecal contents. A Trichomonas pronazeki‐typt flagellate, found in the cecum in 126 (25.4%) of 496 pigs and in the small intestine in 1 of 100. is described as Trichomonas buttreyi n. sp. This organism is relatively small (average length 5.92 ± 0.79 μ, range 4.55‐7.49). ellipsoidal in shape, with 5 to 4 flagella up to twice as long as the body, a relatively high undulating membrane of body length, a narrow axostyle with an inconspicuous capitulum closely associated with the usually oval nucleus, a projecting part of the axostyle that equals about j; of the body length, and a disc‐shaped parabasal body lying dorso‐lateral to the nucleus. In media without cecal extract this species could not be subcultured.

SYNOPSIS. Monolayer primary and secondary cultures of embryonic bovine kidney, spleen, intestinal and testicle cells, and secondary cultures of embryonic bovine thymus, maintained in lactalbumin hydrolysate, Earle's balanced salt solution and ovine serum were observed for a maximum of 21 days after inoculation of E. bovis sporozoites. The sporozoites entered the cells in all of these cultures but underwent development only in primary cultures of kidney and intestinal cells and in secondary cultures of kidney, spleen, thymus, intestinal, and testicle cells. In acellular media, the sporozoites retained motility no longer than 21 hr. In the cell cultures, free motile sporozoites were seen for as long as 18 days after inoculation. Sporozoites entered cells anterior end first; the process of penetration required a few seconds to about a minute. Sporozoites were also observed leaving host cells. Intracellular sporozoites were first seen 3 min after inoculation; they were observed at various intervals up to 18 days after inoculation. In transformation of sporozoites into trophozoites a marked change in size and appearance of the nucleus took place before the change in shape of the body occurred. Trophozoites were first found 7 days after inoculation, multinucleate schizonts after 8 days, and schizonts with merozoites after 14 days. Schizonts containing merozoites were seen only in kidney, spleen, and thymus cells. The mature schizonts were smaller and represented a much lower proportion of the total number than in comparable stages of infections in calves. Schizonts with many nuclei occurred in intestinal cells; the most advanced stage seen in testicle cells was the binucleate schizont. Nuclear and cytoplasmic changes were observed in the infected cells.