Deposition of lipopigment--a new feature of human splenic sinus endothelium (SSE). Ultrastructural and histochemical study.

Lipopigment (LP) deposition was studied in a series of 36 control and 79 pathological spleens. In the control group the LP deposition in SSE was rudimentary and did not display age-dependence. A varying degree of lysosomal and cytoplasmic siderosis was a frequent finding in haemolytic anemia without any significant LP induction. In the acquired secondary storage syndrome and in some inherited lysosomal enzymopathies, the amount of LP in splenic sinus endothelium (SSE) was significantly increased and in some instances its deposition reached very high values. As deposition was not accompanied by any detectable lysosomal lipid storage phenomenon in pulpar histiocytes, the pigmentogenesis is thought to be by a process resembling that for lipofuscin. In ceroid-lipofuscinosis group the SSE affection was of low degree, as seen in other viscera. The LP deposition seems thus to be a prominent, albeit variable feature of human SSE lysosomal pathology and may represent a monotonous response to various stimuli connected with increased demands on the SSE lysosomal system. Only in some lysosomal enzymopathies, typically in sphingomyelinase deficiency was SSE LP deposited progressively and concurrently with the stored lipid. LP deposition was accompanied by an increase in lysosomal enzyme activities but lacked the alkaline phosphatase induction in SSE described in lipid and mucopolysaccharide storage diseases. This and several other features which are reviewed clearly distinguish SSE from the pulpar histiocytes with which they have been often identified.