BONE MARROW, THYMUS AND BLOOD: CHANGES ACROSS THE LIFESPAN

Abstract

The aim of this review is to present age-related changes in the bone marrow and thymus and their effects in later life. Age-related hematologic changes are marked by a decline in marrow cellularity, increased risk of myeloproliferative disorders and anemia, and a decline in adaptive immunity. The exact mechanisms that produce these changes remain undefined. For the most part, the changes in function that are a consequence of aging alone rarely have meaningful clinical consequences. However, in the face of the stresses induced by other illnesses, the decreased physiologic reserve can slow or prevent an appropriate response to the stressors.

Figure 1

Aging of bone marrow and thymus. Bone marrow cellularity declines from birth in a manner comparably to thymic mass. This is reflected histologically by the increased presence of fat. The clinical consequences of these age associated changes, in the absence of disease are a mild anemia and immune deficiency. The latter is reflected by an increased predisposition to certain infections (e.g., herpes zoster or reactivation of latent tuberculosis) and possibly to the increased predisposition to cancer.