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Quantitative Studies on Intracytoplasmic A Particles Formed in DBA/2 Mouse Leukemias¹

Institute for Virus Research, Kyoto University, Kyoto, Japan

Formation of intracytoplasmic A particles in DBA/2 mouse leukemias was studied under various conditions with the fuchsin acid staining method. The A-particle index (API) was defined as the number of cells containing cytoplasmic aggregates of these particles per 100 leukemia cells examined in lymph node smears. API's of five different lymph nodes from the same mice were at almost identical levels. This provided a basis for estimating A-particle formation of the whole body from the API of a single node. The following observations were made: (a) in 322 cases of spontaneous leukemias, API levels varied greatly from case to case, ranging from 0 to 80; (b) males and the aged contained more A particles than their respective counterparts; (c) however, API was almost zero in mice that were nonleukemic; (d) during the natural course of leukemia, API rose significantly in almost one-half of the cases; (e) hormonal stimulation and litter numbers had no effect on API levels; (f) in contrast, transplantation exerted a rather suppressive effect on API levels; (g) API's of thymus and leukemia cells circulating in peripheral blood were considerably different from those of lymph nodes; furthermore, (h) API was linearly related to the mitotic index of leukemia cells; and (i) as in interphase cells, usually a single A-particle aggregate was found in mitotic cells, which was transferred to one "daughter" cell, leaving the other A-particle free; (j) API's in mitotic cells were sometimes at the same level of, and sometimes significantly higher than, those of interphase cells. These observations were discussed in connection with cell population kinetics of DBA/2 mouse leukemia cells.

¹ Supported by Grants 9131, 90172, and 92139 from the Ministry of Education, Japan, and in part by the Kazato Foundation, Tokyo, Japan.

² Present address: First Division, Department of Internal Medicine, Medical Faculty, Kyoto University, Kyoto, Japan.

Received 9/ 5/73. Accepted 2/ 1/74.