Antibodies against Mycobacterium leprae antigen 7 from birth to 18 months of age: an indicator of intra-uterine infection in leprosy.

All babies of three non-leprosy mothers and ten tuberculoid leprosy mothers and four of five babies of mothers with inactive lepromatous leprosy showed a decline in serum concentration of antibodies against M. leprae antigen 7 during the first 4 months of life, as expected from catabolism of maternal IgG. By contrast, ten of twenty babies of mothers with active lepromatous leprosy showed a decline in concentration of anti-M. leprae 7 antibodies considerably less than expected. This indicates that these babies have been stimulated by M. leprae antigen 7, either as free antigen or by viable M. leprae before birth, and thus that leprosy may occur as a congenital infection. Studies of anti-M. leprae antibodies in repeated serum samples obtained during the first 18 months of life indicated that children of mothers with bacilliferous leprosy are frequently exposed to M. leprae to a sufficient extent to stimulate the immune system of the baby to production of anti-M. leprae antibodies during this period. The consequences of this exposure to M. leprae should be ascertained by careful clinical studies.