Читать книгу Pathology of Genetically Engineered and Other Mutant Mice - Группа авторов - Страница 114

The bone marrow occupies the cavities of the trabecular meshwork of the axial and long bones. It is highly vascularized and supplied by nerves, but it lacks lymphatic drainage. The bone marrow forms a network of hemopoietic and nonhemopoietic cells, including endothelial cells, pericytes, fibroblasts, and osteoblasts. Together, these cells form a niche, a microenvironment for HSCs that controls their self‐renewal and differentiation [5]. The HSCs generate progenitor cells that differentiate into erythrocytes, leukocytes, including immature B lymphocytes, and platelets. In addition to its major role in generating blood cells, the bone marrow is also the site where populations of plasma cells and memory T cells reside following their induction in secondary lymphoid organs.

 Examination of bone marrow: Routine assessment of the bone marrow is performed on sections of bones following formalin fixation and decalcification. Decalcification is usually achieved with organic acids such as formic acid or with chelating agents such as ethylenediaminetetraacetic acid (EDTA) solution. The latter procedure takes longer but is preferred for immunohistochemistry because of enhanced antigen preservation. The knee joint with the distal femur and proximal tibia and sternum are good choices. Light microscopy of H&E‐stained sections, preferably less than 4 μm thick, can assess overall cellularity, ratio of erythroid to myeloid precursors, and number of megakaryocytes. Examination of smears or cytospin preparations of bone marrow cells can provide a more detailed analysis of the cellular composition of the bone marrow. Cell suspensions can be obtained by flushing the long bones with a 25G needle and syringe after removing the ends (epi‐ and metaphyses). In depth analysis of the cellular composition of bone marrow and the different maturation stages of blood cell lineages requires flow cytometry of cells labeled with fluorochrome‐conjugated antibodies.

 Hypoplasia and aplasia: Mutations or chemical treatments that induce DNA damage or interfere with cell division will induce bone marrow aplasia, a general loss of all hematopoietic lineages. Hematopoietic cells are absent, and bone marrow space is filled with venous sinuses and a few adipocytes (Figure 7.1). Such changes are often associated with a reduction of the red pulp of the spleen. Loss of specific lineages may be seen with genetic deletion of growth factors. A selective decrease of erythropoiesis is associated with chronic inflammation. There is increased myelopoiesis and an increase of hemosiderin.

 Hyperplasia: Increased numbers of hematopoietic cells may involve all or selected cell lineages. The hyperplasia is usually the result of increased demand induced by increased secretion of growth factors or cytokines, and is typically associated with increased extramedullary hematopoiesis (EMH) in the spleen and liver. An increase of erythropoiesis is caused by anemia and may be associated with megakaryocyte hyperplasia if there is loss of platelets. Increased myelopoiesis is often seen with chronic inflammation and can result in a dramatic shift of the myeloid:erythroid ratio.Figure 7.1 Bone marrow. Bone marrow hypoplasia four days after deletion of Cul4A in Cul4a/Pcid2tm2Ktc mice (b) compared with C57BL/6J mice (a). (c) Fibro‐osseous lesions in 821‐day old female 129S1/SvlmJ and 427‐day old female KK/H1J (d) mice. Higher magnification of fibro‐osseous lesion (e).

 Aging‐associated changes: The overall cellularity of the bone marrow in old mice remains high at >90% in contrast to humans in which the hematopoietic cells are gradually replaced by adipocytes, although there are strain and regional differences in the distribution and accumulation of adipocytes. Aging is associated with an increased number of HSCs, increased myelopoiesis, and increased accumulation of plasma cells. The plasma cells promote myelopoiesis through the local secretion of inflammatory cytokines [6]. These changes may be difficult to assess in routine H&E sections of the bone marrow. Fibro‐osseous lesions are proliferative alterations comprised of fibrovascular tissue intermixed with fine bone trabeculae in the bone marrow of aged mice (Figure 7.1). Although they replace hemopoietic tissue, the lesions are not sufficiently expansive to compromise the production of hemopoietic cells. Fibro‐osseous lesions occur predominantly in female mice with a high incidence in B6C3F1 mice and in certain inbred strains including 129S1/SvImJ, KK/H1J, and NZW/LacJ [7–9].