Impairment of Jones‐Mote Hypersensitivity and Specific Antibody Response against Depolymerized Flagellin in Lepromatous Leprosy

Cutaneous hypersensitivity and antibody‐producing capacity were assessed in patients with lepromatous leprosy with defective immunity, by immunizing them with monomeric flagellin from Salmonella adelaide Results were compared with those of controls, matched for age and sex, derived from similar socioeconomic stratum, but without any defect of the immunological system. In contrast to the normal individuals, who showed Jones‐Mote type of hypersensitivity, no lepromatous patient could mount any ‘delayed‐in‐time’ cutaneous hypersensitivity reaction against an intradermal challenge of monomeric flagellin. However, when immunized through the subcutaneous route, both groups could produce adequate amounts of specific serum antibody. In addition to this unique split tolerance found in all lepromatous patients, some patients showed low levels of ‘natural’ IgM antibody, reduced formation of specific antibody when immunized through the subcutaneous route, and incomplete maturation of IgG class of anti‐flagellin antibody. When immunized by the intradermal route, however, production of both anti‐flagellin antibody and maturation of IgG antibody was significantly inhibited in normal adults but not in lepromatous patients. Thus, contrary to the earlier concept of hyperactivity of the humoral immune apparatus in lepromalous leprosy, the present study detected B‐cell hypofunction in some patients.