Infants and children with haematological disease

Summary The aim of the present work was to study certain aspects of the kinetics of bone marrow cell proliferation in normal children and in children with haematological disease. In addition to haematological techniques the following methods were used with bone marrow aspirates: semiquantitative assessment of the cellularity, differential cell counts, and study of the proliferative activity of the cells by means of in vitro one hour incubation with tri‐tiated thymidine and stripping film autoradiography. Labelled thymidine incorporation into nuclear. DNA was estimated by determining the distribution of developed silver grains over the cells (grain count). The relative number of labelled cells (labelling index) is a measure of the proliferative activity. Chapters I and II comprise a description and critical discussion of the methods used. Some technical modifications were introduced in order to improve the reproducibility of the methods. The use of the brush technique for making smears was shown to give a reasonably uniform distribution on the smear of all cell types, except megekaryocytes, and a low percentage of disintegrated cells. The introduction into the classification system of a cell group designated ‘stem cells’ was proposed. This group conforms to the following morphological criteria and labelling behaviour: (a) the cells are mononuclear with a finely reticular chromatin and usually visible nucleoli, i.e. are immature, (b) they lack definite characteristics of any differentiated cell line, i.e. are undifferentiated, and (c) they have the capacity to incorporate thymidine, i.e. are proliferative. The proliferating and non‐proliferating pools were defined in the erythropoietic and granulopoietic cell lines on the basis of their labelling behaviour. Chapter III describes the findings in 60 healthy infants and children, aged from a few hours to 8 years, special attention being paid to the situation during the first month of life, and more especially to the first week. The results of the differential counts confirmed and extended the results of previous investigations. ‘Stem cells’, as defined above, were present in all smears in significant proportions, the range of variation being relatively small. During the first week of life the labelling index of the ‘stem cell’ pool was low but then gradually increased, attaining at about one month a value which then remained fairly constant. The labelling indices within the erythropoietic and granulopoietic pools were quite constant throughout the age period and did not differ significantly from the results of comparable investigations in adults. The ratio between non‐proliferating and proliferating erythroblasts, however, decreased during the first month, after which it remained essentially constant. These findings were interpreted as indicating a rapid neonatal decrease in erythropoietic activity during this age period and confirm the results of previous investigators, who came to the same conclusion using other methods. Furthermore the results of the present study indicate that the decrease is due to a reduction in cellular proliferation at the ‘stem cell’ level. Chapter IV describes studies of: A. Haemolytic disease of the newborn; B. Congenital hypoplastic anaemia; C. Infantile genetic agranulocytosis; and D. Pancytopenia. A. Five neonates with haemolytic disease due to incompatibility within Rh‐groups between mother and child were investigated during the first day of life and before any exchange transfusion had been made. The only abnormal finding was that the labelling index of the ‘stem cell’ pool was considerably higher than that of healthy neonates. Haemolytic disease of the newborn is thus characterized by an increased proliferative acitivity of the ‘stem cell’ pool and an apparently normal proliferation and maturation within the medullary erythropoietic cell line. B. Three infants with Congenital (erythroid) hypoplastic anaemia were investigated prior to corticosteroid therapy. The bone marrow differential counts were normal except for low numbers of erythroblasts, the deficiency being greater in the more mature compartments. The labelling indices of the ‘stem cell’ and granulopoietic pools were normal except for a low index of the ‘stem cell’ pool in one of the cases. The labelling index of the erythropoietic pool was apparently subnormal in two cases and normal in one. The findings were interpreted as indicative of a low influx from the ‘stem cell’ pool to the erythroid cell line and ‘ineffective’ erythro‐poiesis, i.e. cell death, within the eryth‐ron. The pathophysiological disturbances appear to be those expected from either a deficiency of erythropoietin or a blocking of its effect, the latter being more likely, as an elevated serum erythropoietin level is a frequent finding in this disease. This would imply that erythropoietin is essential for both transformation of ‘stem cells’ and development of differentiated stages. C. Three children with Infantile genetic agranulocytosis were studied, one of them with repeated bone marrow aspirations during the age period two weeks to six months. In all cases there was a severe neutropenia and a varying degree of monocytosis in the peripheral blood. The bone marrow differential counts showed a marked reduction of myelocytes and mature neutrophils. ‘Stem cells’ and erythroid elements were normal except for one low value of the ‘stem cell’ labelling index in one of the cases. The labeling indices of the granulopoietic compartments showed a tendency to low values in myelocytes and close to nor‐ mal values in promyclocytes. These findings were interpreted as indicating that the transformation of ‘stem cells’ to promyclocytes was normal, but that there was a destruction of cells in later stages. D. Three cases with pancytopenia were investigated, Two of the cases showed many features in common: bone marrow hypocellularity, a very low number of megakaryocytes, a low ‘stem cell’ labelling index, and no marked signs of disturbances in the development of the erythropoietic and granulopoietic cell 1inr.s. These findings were interpreted as indicating that the bone marrow insufficiency was mainly due to a reduced flow from the ‘stem cell’ pool to the differentiated cell lines. The third case showed a hypercellular bone ninrrow with abundant megakaryocytes and very abnormal distribution within the differentiated cell lines but also a low ‘stem cell’ labeling index. In this case, the pancytopenia seemed to be due, mainly to destruction of cells during maturation and only to some extent to reduced influx from the ‘stem cell’ pool.