Isospora felis: Development in Cultured Cells with Some Cytological Observations

Abstract

Isopora felis undelwent development in monolayer cultures of human cells (embryonic intestine, esophageal epithelium, amnion, lung, and epithelioid carcinoma of the cervix) as well as cells from embryonic bovine trachea, canine kidney, and chick kidney. Pairs of daughter organisms developed by endodyogeny and possibly schizogony. Special stains were used to study the cytological changes that occurred during development. Disappearance of red-stained material from the refractile body in organisms stained with Whipf's polychrome stain suggested utilization or conversion of this material by the sporozoite or change in its ionic nature; its reappearance in mature daughter organisms suggested replacement, reconversion, or return to the previous ionic composition for the next generation. Carbohydrate, identified as periodic acid-Schiff positive granules, also appeared to be utilized by the sporozoites and replaced in the mature daughter organisms. Nucleic acids were identified in the cytoplasm and the nucleus of sporozoites and daughter organisms by staining with gallocyaninchromalum after RNase or DNase digestion. The distribution of nucleic acids in these two stages was similar. Several species of Isospora have developed in cultured cells (Turner and Box, 1970; Fayer, 1972; Fayer and Kocan, 1972; Fayer and Mahrt, 1972). However, previous attempts to obtain development of I. felis have been unsuccessful. Sheffield and Melton (1970) inoculated monkey kidney cell cultures with mixture of Toxoplasma gondii, I. felis, and I. rivolta and found that a typical T. gondii infection resulted. They also inoculated similar cultures with mixture of I. felis and I. rivolta sporozoites and found no intracellular organisms. Shibalova and Petrenko (1972) inoculated cultures of chick fibroblasts, quail fibroblasts, monkey kidney, human embryo, rabbit, sheep embryo, green marmoset, and human amniotic cells with sporozoites of I. bigemina, I. felis, and I. revolta. Each of the three species entered cells, but only I. bigemina appeared to have undergone development. The present study represents further attempt to obtain development of I. felis by employing some of the same cell types used by previous investigators as well as several different cell types. This study also represents the first investigation of cytochemical changes of an isosporan in cell culture. Received for publication 5 July 1973. *Animal Parasitology Institute, Beltsville Agricultural Research Center, ARS, Beltsville, Maryland 20705. MATERIALS AND METHODS