Sera of leprosy patients with type 2 reactions recognize selective sequences in Mycobacterium leprae recombinant LSR protein.

Type 2 reactions (erythema nodosum leprosum [ENL]) are episodic, reactional states causing significant morbidity in lepromatous leprosy patients. With a view to defining the immunological differences between the stable and reactional forms of lepromatous leprosy, we determined antibody responses to LSR, a recombinant protein of Mycobacterium leprae previously described by us (S. Laal, Y.D. Sharma, H.K. Prasad, A. Murtaza, S. Singh, S. Tangri, R. S. Mishra, and I. Nath, Proc. Natl. Acad. Sci. USA 88:1054-1058, 1991), as well as to 10- to 15-mer overlapping peptides synthesized on the basis of the LSR amino acid sequence. We report here the selective recognition of B cell epitopes by sera from patients with ENL as compared with a control group with nonreactional lepromatous leprosy. Peptides 2 and 3, with the sequences GVTYEIDLTNKNAA and IDLTNKNAAKLRGD, respectively, were recognized by > 95% of sera from patients with active ENL. Peptide 3 in addition showed reactivity with sera taken from 91.6% of lepromatous leprosy patients who were apparently stable but who were recorded to have had ENL several weeks before or after the sample collection. The core sequence IDLTNKNAA common to both these peptides may be a major target of humoral responses in ENL. In addition, the RGD motif at the C terminus appeared to influence the antigenicity of peptide 3 in enzyme-linked immunosorbent assay. It would appear that humoral responses during ENL are directed to selective antigenic determinants of the leprosy bacillus. The use of such serological markers to identify lepromatous leprosy patients with a high risk for developing ENL would be of clinical and predictive value.