In
asthma, it has been hypothesized that suppressor T-lymphocytes play a protective role and have been reported to be functionally abnormal. Thymic
hormone thymulin plays a role in the differentiation of T-lymphocytes and plasmatic
thymulin concentration and is related to the functional state of the thymus. To assess the participation of the thymus in the impairment of T-lymphocyte function, we measured plasma
thymulin activity in children with allergic
asthma (N = 40). The plasma
thymulin activity was compared with plasma
thymulin activity of children with nonallergic
asthma (N = 6), children with
atopic dermatitis (N = 9) or
allergic rhinitis (N = 7), and in age-matched healthy control children (N = 18) (age range of children studied, 2 to 19 years).
Thymulin activity was found within the normal range (1/16 to 1/64) in all control children and in all children with allergic
asthma and
allergic rhinitis, as well as in all children with intrinsic
asthma and
atopic dermatitis. Our findings are at variance with the low
thymulin activity previously reported in allergic
asthma, and we could not explain these discrepancies. (Both studies used the same bioassay, and the population studied did not appear to be different.) T-lymphocyte abnormalities in subjects with
asthma must be assessed by other means than measurement of thymic function.