Bf. Haynes et al., The role of the thymus in immune reconstitution in aging, bone marrow transplantation, and HIV-1 infection, ANN R IMMUN, 18, 2000, pp. 529-560
The human thymus is a complex chimeric organ comprised of central (thymic e
pithelial space) and peripheral (perivascular space) components that functi
ons well into adult life to produce naive T lymphocytes. Recent advances in
identifying thymic emigrants and development of safe methods to study thym
ic function in vivo in adults have provided new opportunities to understand
the role that the human thymus plays in immune reconstitution in aging, in
bone marrow transplantation, and in HIV-1 infection. The emerging concept
is that there are age-dependent contributions of thymic emigrants and proli
feration of postthymic T cells to maintain the peripheral T cell pool and t
o contribute to T cell regeneration, with the thymus contributing more at y
ounger ages and peripheral T cell expansion contributing more in older subj
ects. New studies have revealed a dynamic interplay between postnatal thymu
s output and peripheral T cell pool proliferation, which play important rol
es in determining the nature of immune reconstitution in congenital immunod
eficiency diseases, in bone marrow transplantation, and in HIV-1 infection.
In this paper, we review recent data on human postnatal thymus function th
at, taken together, support the notion that the human thymus is functional
well into the sixth decade and plays a role throughout life to optimize hum
an immune system function.