Distribution of age-related thymulin titres in normal subjects through thecourse of life

The thymus has a dominant immunological role in utero and in early childhoo d, being a primary source of T lymphopoiesis, and its investigation may be particularly relevant for the immunological study of paediatric patients. T hymulin, a nonapeptide secreted by the thymus, is an essential hormone for T lymphocyte differentiation and function. As thymulin values in the normal population have not been well documented, especially for children under th e age of 1 year, we detail thymic endocrine function by presenting age-rela ted plasma thymulin levels in a large series (n = 93) of healthy individual s, ranging from birth to old age. We demonstrate that thymulin is already d etectable at birth; it then gradually increases with age, reaching the high est level in children aged 5-10 years. Starting at adolescence, thymulin ti tres gradually start to fall, reaching the lowest value at 36 years of age and remaining steady until 80 years (the oldest person tested).