A study of cellular immunity in clinically healthy children of parents with leprosy in northern Thailand.

A study was done of the response to PPD-tuberculin, candida and the tuberculin conversion rate after BCG vaccination among 302 healthy children in northern Thailand. The children were grouped according to whether their parent(s) or other household contact(s) had tuberculoid leprosy (74 children), lepromatous leprosy (47 children), or all family members were healthy (181 children). No significant differences were detected in the responses to candida or PPD-tuberculin on initial skin testing or in the history of a previous BCG vaccination in the three groups of children. However, among the children who were initially tuberculin negative, significantly decreased PPD conversion rates occurred in children from lepromatous families in comparison to those from tuberculoid families (p less than 0.01) or normal families (p less than 0.05). In the children from lepromatous families who were initially PPD and candida negative, 0 of 3 developed PPD-tuberculin conversions after BCG in comparison to 12 of 14 (85.7%) from normal families (p = 0.015). These data indicate that some children from lepromatous families were relatively unresponsive to stimulation with BCG and possibly other mycobacterial vaccines. The immunopathogenesis of this relative unresponsiveness should be further defined, since it might have important implications for the prevention of leprosy with a vaccine.