AIMS--To compare the numbers of alkaline phosphatase positive reticulum cells (AL-RC) and macrophages in bone marrow transplant (BMT) recipients with numbers in normal subjects and to look for correlations with clinical features. METHODS--Sections of femoral marrow were obtained at necropsy from 18 BMT recipients and nine normal subjects who had died suddenly. AL-RC were visualised through their endogenous alkaline phosphatase activity. Macrophages were stained by an immunocytochemical technique using the antibody EBM/11 (CD68) and through their endogenous acid phosphatase activity. The numbers of stained cells were counted and expressed as a percentage of total nucleated cells. RESULTS--In both sets of marrow tissue, more macrophages stained for CD68 than for acid phosphatase, indicating macrophage heterogeneity. The percentage value for CD68 positive macrophages was higher among the transplant recipients (p < 0.01). At least in part this was caused by a reduction in haemopoietic cell numbers. Percentage values for acid phosphatase and alkaline phosphatase positive cells did not differ between the two groups. To exclude the effect of changes in marrow cellularity, stromal cell ratios were compared. The AL-RC: CD68 and acid phosphatase:CD68 ratios were both lower in BMT recipients, indicating that after BMT either the absolute number of AL-RC and acid phosphatase cells decreases, or CD68 cells increase, or there is a combination of the two. There was no correlation between the number of each cell type and cell dose given at transplantation, time after transplantation, presence of graft versus host disease or infection, marrow erythroid:myeloid ratio, or peripheral white cell count. The ratio of AL-RC to macrophages in our intact marrow was 0.43, considerably higher than that reported in cultured marrow. CONCLUSIONS--AL-RC and acid phosphatase positive cells may be most important for supporting haemopoiesis and their reduction after BMT may contribute to depression of haemopoiesis. CD68 positive cells include macrophages with a wide variety of functions and these may be increased in response to marrow damage.
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