Thymus volume correlates with the progression of vertical HIV infection

The thymus is the organ responsible for the maturation and selection of T lymphocytes and is thus pivotal in allowing the development of a functional immune system. Because in HIV infection cell-mediated immune responses are severely impaired, we studied the role of thymus in the control of the progression of HIV infection to AIDS. Thymic volume was analysed by magnetic resonance imaging in 31 vertically HIV-infected children. Plasma HIV viral load and phenotypic and functional cellular immunity-defining parameters were examined in the same patients. Thymic volume was not correlated with age or nutritional status; thymic volume was nevertheless correlated with CD4 T-lymphocyte counts and with the percentage and absolute number of CD45RA+CD62L+ (naive) T lymphocytes. In addition, the ability of peripheral blood mononuclear cells to proliferate upon tetanus stimulation was directly proportional to thymic volume. Finally, a negative correlation was detected between thymic volume and HIV viral load. Because low HIV plasma viraemia and preserved immune function are favourable prognostic indices in HIV disease, these data indicate that an immunological, thymic-dependent control of the progression of HIV infection might be possible, at least in vertically transmitted HIV infection.