Altered basement membrane structure of the spleen in hairy cell leukaemia. Demonstration of laminin in hairy cells.

Changes in five spleens affected by hairy cell leukaemia were characterized using immunohistochemical staining for the basement membrane (BM) components laminin and type IV collagen. The ring fibres had not been totally destroyed, and were well preserved in places. The spaces filled by abnormal blood or hairy cells were assigned to the categories of altered sinus and two types of pseudosinus. In an altered sinus the staining pattern of the ring fibres had gained attenuations and the sinus was sometimes lined by a continuous BM of uneven thickness. The number of altered sinuses was related to the size of the spleen. The pseudosinuses were larger than normal sinuses and usually also larger than altered sinuses. One of the two types seemed to be derived from ruptured Billroth's cords and entailed spaces of irregular size and shape bounded by strips of fibres containing BM proteins. No ring fibres were seen in the wall. The other type of pseudosinus occurred in those spleens where no white pulp remained. These spaces were large, located around arteries and bounded by irregular strips of BM material. In three cases a number of hairy cells could be demonstrated which showed positive staining for laminin either in the surface or in the cytoplasm. Adhesive properties of hairy cells would be conceivable on the basis of the presence of laminin on the surface of the cells.