Boosting immunity?

In collaboration with the Haematology Department (Drs Yves Beguin and Frédéric Baron) and the Immunology Department (Dr Michel Moutschen) of the Liège CHU, as well as the Virology Department at the Pasteur Institute in Paris (Dr Rémi Cheynier), Professor Geenen's team were able to draw conclusions and produce new hypotheses about the relationship between growth hormone and thymus activity. The researchers first observed that stopping growth hormone treatment triggered a decrease in IGF-1 levels, which was to be expected, and which depends on the growth hormone. However, they also observed a very clear reduction in thymophoiesis and the intrathymic proliferation of T lymphocyte precursors. “Looking at the TREC level, we can see that it drops as treatment is stopped. This correlates perfectly with a reduction in the level of IGF-1. One month after treatment is reintroduced, all parameters have almost returned to the levels measured before treatment with growth hormone injections was stopped" explains Vincent Geenen. Maintaining production of T lymphocytes by the thymus in adults is therefore linked to growth hormone. “It is probably IGF-1 which is most significant in terms of T lymphocyte production", continues Professor Geenen.

The next stage for the researchers was to attempt to see in vitro which cells are required for thymus function. “Without a doubt, IGF-1 is produced from within the thymus, but a doubt remains as to the precise nature of the cells which produce this growth factor", says Vincent Geenen.

Moreover, the researchers plan on initiating a study to find out if it would be possible, based on this new knowledge, to increase the immune response to vaccines in elderly people, or to reinforce the immune defences of immunodeficient patients. “Chemotherapy sessions, for example, destroy the immune system, which regenerates very slowly afterwards. It would be interesting to see if, in this case, treatment with growth hormone could accelerate regeneration by increasing the production of T lymphocytes” suggests Vincent Geenen.

But he warns against his team's results being misinterpreted: “It would be a shame if this article encourages fraudulent doctors who say that growth hormone is an anti-ageing hormone and that it will improve immune function. That is not true. Our study simply shows that in patients with a well-documented growth hormone deficiency, there is a reduction in the level of growth hormone which has an effect on the efficacy of certain immune functions.”