Low circulating thymulin-like activity in children with AIDS and AIDS-related complex.

Thymic secretory function was assessed by determining levels of circulating thymulin-like activity in plasma of 21 pediatric patients infected with the HTLV-III/LAV retrovirus. All the patients had serum antibodies against p41 antigens of HTLV-III on Western blot analyses. In accordance with the latest definition established by the Centers for Disease Control, 14 patients had the acquired immunodeficiency syndrome (AIDS) and the remaining 7 were classified as having AIDS-related complex. Their ages ranged from 1 to 7 years, with 10 being less than 1 year of age. Circulating thymulin activity, normally highest in healthy children under 15 years of age, was undetectable in 11 patients and below normal range for age in the remaining. OKT4/OKT8 ratios of T-cell subsets in peripheral blood were below normal in the majority of patients. Our findings suggest that thymic epithelial injury may be an early event in HTLV-III/LAV-related disease and may precede the development of clinical and/or immunologic aberrations.