Quantitative Studies of Haemopoietic Spleen Colonies in Rats treated with Cytotoxic Chemicals

Abstract

Summary. Quantitative studies of spleen colonies in rats are reported in some detail and the findings are compared with those reported for spleen colonies in mice, and with those of the only other extensive report on rat spleen colony histology. While similarities are observed between the two studies on rat spleen colony histology, there are marked differences between these results and those that are obtained in mice. The reasons for these differences are discussed and it is concluded that the haemopoietic micro‐environment of the rat spleen is considerably different from that in the mouse, and that this is probably the major reason accounting for differences in rat and mouse spleen colony histology.

Capacity of Rat Haemopoietic Colony-Forming Units to Produce Differentiated Progeny

“…The number of surface spleen colonies at various times after the transplanta tion of bone marrow or spleen cells was assessed using a X 2 magnification hand lens after fixation of the spleen in Carnoys fixative for 1-2 h [5]. The total num ber and histological type of colony in both the spleen and femoral bone marrow were obtained from microscopical analysis of 5-um-thick serial, longitudinal sec tions stained in haemotoxylin and eosin [5,7].…”

“…Bone marrow cell suspensions were prepared by flushing out the marrow, with TC199, from both femurs of up to 5 donor rats and aspirating the suspension through a 19-gauge needle to obtain a separated cell suspension [5], Spleen cell suspensions were prepared by forcing spleens through stainless steel gauzes of gradually decreasing mesh size and, finally, through a 19-gauge needle. The num ber of cells in each suspension was determined using haemocytometers.…”

“…The total num ber and histological type of colony in both the spleen and femoral bone marrow were obtained from microscopical analysis of 5-um-thick serial, longitudinal sec tions stained in haemotoxylin and eosin [5,7]. Except for megakaryocytic colonies (where 5 megakaryocytes or more were considered a colony) more than 100 cells were classified as a colony which was considered pure, i.e., consisting of one cell line only, unless it contained more than 10% of another cell type [5,7].…”

“…In both studies it was evident that a high proportion of rat spleen colonies consisted either entirely of cells, arbitrarily termed 'undifferen tiated', which were too immature to classify as belonging to any one haemopoietic cell line, or of a mixture of these cells with recognizable erythroid cells ['erythrocyte variant'; 6]. Data were also presented [5] which showed that unlike spleen colonies in mice, rat spleen colonies in creased in number as the time for colony development was extended from 7 or 8 to 12 days. This change was associated with a shift towards a higher proportion of colonies consisting of undifferentiated cells.…”

“…The dif ference in the proportion of CFU lost by differentiation in the spleen and bone marrow could explain the different CFU population doubling times in these two organs [4]. Two detailed reports [5,6] have considered the histology of bone marrow-derived colonies in the spleens of rats treated with cytotoxic chem icals. In both studies it was evident that a high proportion of rat spleen colonies consisted either entirely of cells, arbitrarily termed 'undifferen tiated', which were too immature to classify as belonging to any one haemopoietic cell line, or of a mixture of these cells with recognizable erythroid cells ['erythrocyte variant'; 6].…”