John E. Ubelaker

Ultrastructural and immunohistological characterization of the SIRC corneal cell line

SummaryA widely utilized rabbit corneal cell line, SIRC, was characterized ultrastructurally and immunohistologically. Although SIRC cells are often described as being of epithelial origin, important ultrastructural and antigenic characteristics indicate that these cells are fibroblastic and not epithelial. SIRC cells lack desmosomes, cytoplasmic filaments, and cytokeratin—structures that are characteristic of corneal epithelial cells. By contrast, the dendritic morphology, presence of vimentin, and the extensive dense accumulations of ribosomes and rough endoplasmic reticulum are consistent with a fibroblastic phenotype. Collectively, the morphology, ultrastructural features, and antigenic composition favor the hypothesis that SIRC cells are fibroblastic cells (keratocytes) and not corneal epithelial cells.

SYSTEMATICS OF SPECIES REFERRED TO THE GENUS ANGIOSTRONGYLUS

Based on morphological criteria of the male bursa, angiostrongylid nematodes often placed in the genus Angiostrongylus Kamensky (1905) were found to be heterogeneous, comprising species which are relegated to 5 distinct genera: Angiostrongylus Kamensky, 1905 (syn. Haemostrongylus Railliet and Henry, 1907); Parastrongylus Baylis, 1928 (syn. Pulmonema Chen, 1935, Rattostrongylus Schulz, 1951, Morerastrongylus Chabaud, 1972, Chabaudistrongylus Kontrimavichus and Delyamure, 1979); Angiocaulus Schulz, Orlov and Kutass, 1933; Gallegostrongylus Mas-Coma, 1977 (syn. Thaistrongylus Ohbayashi, Kamiya and Bhaibulaya, 1979 n. syn); and Stefanskostrongylus Drozdz, 1970. These genera all contain species located primarily in specific host groups: Angiostrongylus in carnivores; Parastrongylus in rodents (Muridae), Angiocaulus in mustelids; Rodentocaulus in rodents (Cricetinae), Gallegostrongylus in rodents (Muridae), and Stefanskostrongylus in insectivores. Species in each genus include: Angiostrongylus (A. vasorum, A. raillieti, A. chabaudi); Parastrongylus (P. tateronae, P. cantonensis, P. mackerrasae, P. sandarsae, P. sciuri, P. petrowi n. comb., P. dujardini, P. schmidti, P. costaricensis n. comb., P. malaysiensis n. comb., P. ryjikovi n. comb., P. siamensis n. comb.); Angiocaulus (A. gubernaculatus, A. ten n. comb., A. sp. Caballero, 1951); Rodentocaulus (R. ondatrae) and Gallegostrongylus (G. ibicensis, G. andersoni, G. harinasutai n. comb.). Angiostrongylus pulmonalis is likely similar to Stefanskostrongylus soricis and is transferred to this genus. Angiostrongylus minutus is removed to Stefanskostrongylus.

In vitro penetration of human corneal epithelium by Acanthamoeba castellanii: a scanning and transmission electron microscopy study.

Human corneal buttons were exposed to Acanthamoeba castellanii trophozoites and cysts for 12 hours at 35°C. The buttons examined by light microscopy and scanning and transmission electron microscopy had severe epithelial ulceration and penetration by trophozoites. Observations on trophozoites below the surface suggest that penetration is accomplished by both secreted cytolytic enzymes and phagocytosis. It is likely that the secretion of one or more enzymes constitutes the initial step in preparing the host tissue for endocytosis or that the secretory mechanism is used by the amebas to move through the outer squamous layer to the basement epithelium where phagocytosis occurs. Based on this study and a previous study, it appears that entry into the cornea is a two-step process involving adherence and penetration by trophozoites.

A role for elevated plasma corticosterone in modulation of host response during infection with Trichinella pseudospiralis

Summary Suppression of host inflammatory response in mice infected with Trichinella pseudospiralis was associated with host plasma corticosterone levels significantly higher than those seen in uninfecled mice or in mice infected with T. spiralis. Increases in the population of mitochondria and depletion of lipid droplets in cells of the zona fasciculata were seen in the adrenals of mice infected with T. pseudospiralis. Elevations in enteritis, myositis and myocarditis accompanied 100% mortality in adrenalectomized mice infected with T. pseudospiralis, while lower levels of inflammation and no mortality were observed in sham operated or intact animals infected with this parasite. The severe myositis normally accompanying infection with T. spiralis was suppressed by concurrent infection with 1000 or 2000 T. pseudospiralis to levels equivalent to those seen in animals receiving 015 and 0‐41 mg cortisone acetate/25 g mouse/day, respectively.

The fine structure of spermatogenesis in Hymenolepis diminuta (Cestoda) with a description of the mature spermatozoon

SummaryThe processes of spermatogenesis and spermiogenesis in Hymenolepis diminuta were studied by electron microscopy using improved preparative techniques. Spermatogonia (Type A) are characterized by nuclei 3.79 (±0.17) μm in diameter, dense cytoplasm packed with free ribosomes, and aggregates of mitochondria. After mitoses, certain spermatogonia (Type B) assume syncytial rosettes containing eight nuclei. Primary spermatocytes maintain the rosette syncytium and have large nuclei (4.28±0.24 μm in diameter), smooth endoplasmic reticulum, and polysomes. The secondary spermatocyte is short-lived and is characterized by nuclei (2.0±0.11 μm in diameter) and perinuclear membranous lamellae. The syncytial spermatid cluster contains avoid nuclei which condense and elongate to a final diameter of 0.22±0.04 μm. Once elongated, these nuclei become delimited from the syncytium by invaginations of the plasma membrane. During delimitation, cortical peripheral microtubules arise beneath the spermatozoon plasmalemma and a 9+1 axoneme extends the length of the mature lance-shaped spermatozoon.

Scanning electron microscopy of the eggs of Ascaris lumbricoides, A. suum, Toxocara canis, and T. mystax.

Eggs of Ascaris lumbricoides, A. suum, Toxocara canis, and T. mystax were examined by scanning electron microscopy (SEM). All species under study exhibited pronounced surface ridges. The ridges formed distinctive patterns in T. canis and T. mystax. In the Ascaris species, the ridges are similar except that they are more pronounced in the eggs of A. suum. Operculumlike structures were observed only in Ascaris. Correlation of data from SEM with previously reported transmission electron microscopy suggests that the surface ridges seen in Ascaris eggs are formed by the chitinous layer of the shell.

The fine structure of the cysticercoid of Hymenolepis diminuta

SummaryElectron microscopy of the outer wall of the capsule of the eight-day old Hymenolepis diminuta cysticercoid shows it to be part of a syncytium. The surface cytoplasm is a continuous layer connected by arm-like projections to a nucleated cytoplasm lying beneath the surface. The free surface of the outer cytoplasm is greatly increased by numerous branched microvilli. In addition to the syncytium, a separate cell type is described and evidence is presented for its involvement in the formation of the basement layer and other fibrous components of the cystic wall. The possible functions of branched microvilli are commented upon.

Relationship of South American cricetines to rodents of North America and the Old World

ABSTRACT The occurrences of sigmodontine rodents in the Hemphillian Land Mammal Age of Arizona and northern Mexico have been offered as evidence for a North American origin of South American cricetines from a common ancestor of peromyscines, Copemys. The discovery of neotomines and peromyscines associated with sigmodontines in the Hemphillian of central Mexico, combined with the previously reported evidence of ectoparasite distributions and the distribution of nematode endoparasites belonging to the genus Parastrongylus suggest a dual origin of New World cricetines. These data are consistent with the hypothesis that the North and South American cricetines did not have a common New World ancestor. The Copemys–peromyscine lineage may have had an origin from eumyines independent of the Old World cricetodontines, or evolved directly from the Old World cricetodontines and migrated to the New World.

EXPERIMENTAL INFECTION OF SIGMODON HISPIDUS WITH THIRD-STAGE LARVAE OF ANGIOSTRONGYLUS COSTARICENSIS

Adult Sigmodon hispidus, were given 50 third-stage larvae of Angiostrongylus costaricensis orally, intraperitoneally, subcutaneously, and on abraded and unabraded skin. Larvae could not penetrate unbroken skin but established normal infections in the cecal vasculature by all other routes. Significantly more adults were recovered after oral and intraperitoneal inoculation than subcutaneously or through abraded skin. In a single animal given larvae subcutaneously, adult worms were recovered from the pulmonary arteries, an abnormal location for this species of metastrongylid nematode, which usually occurs in the ileocolic mesenteric arteries.

In Vitro Intercellular Adherence of acanthamoeba castellanii: A Scanning and Transmission Electron Microscopy Study

Human corneal buttons were exposed to trophozoites and cysts of Acanthamoeba castellanii for 12 hours. Examination of the buttons by scanning electron microscopy showed numerous trophozoites on the surface of the epithelium. Trophozoites examined by transmission electron microscopy had limited regions of attachment to the epithelium but extensive regions of attachment to each other. Attachment regions were characterized as plaque-like maculae of an incomplete desmosome junction. Firm attachment mechanisms may explain how penetration of the human cornea occurs.