Vol. 29, No. 10 Serology and Leprosy: Immunoassays Comparing Immunoglobulin G Antibody Responses to 28- and 30-Kilodalton Proteins Purified from Mycobacterium bovis BCG MARIA CRISTINA VIDAL PESSOLANI,'t* JOSE MAURO PERALTA,2 FRANKLIN D. RUMJANEK,3 HARRISON MAGDINIER GOMES,1 MARIA ANGELA DE MELO MARQUES,' ELZA CARMEM CERQUEIRA ALMEIDA,4 MARIA HELENA FERES SAAD,1 AND EUZENIR NUNES SARNO' Setor de Hanseniasel and BioManguinhos,4 Fundaqcao Oswaldo Cruz, and Departamentos de Imunologia2 and Bioquimica,3 Centro de Ciencias da Sau'de, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil Received 6 March 1991/Accepted 22 July 1991 Two major proteins from Mycobacterium bovis BCG culture filtrates with molecular masses of 28 kDa (P28) and 30 kDa (P.), identified as components of the BCG 85 complex, were purified and used in enzyme-linked immunosorbent assays (ELISAs) for the determination of specific immunoglobulin G (IgG) levels in patients with leprosy or tuberculosis or with exposure to these diseases. High reactivity to both antigens was observed with sera from lepromatous leprosy patients, whereas antibody levels in sera from paucibacillary leprosy patients were not significantly different from those in sera from healthy individuals from an area in which leprosy is endemic. High IgG responses were also found in some contacts of lepromatous leprosy patients. A comparison of the levels of anti-P28 and anti-P30 within the multibacillary leprosy patient group showed much higher IgG reactivity to P28 than to P30, suggesting that the antibody response of lepromatous patients is directed predominantly against the 28-kDa protein. A high degree of correlation in values of ELISAs based on P2. and on the phenolic glycolipid of Mycobacterium leprae was observed in all groups analyzed. The potential use of an assay based on the 28-kDa protein to selectively distinguish individuals destined to develop multibacillary leprosy is discussed, as also is the likelihood that the 28-kDa-30-kDa complex, part of the fibronectin-binding family, is an important component of M. leprae. Infection with mycobacteria induces a complex immune response in the host which involves both cellular immune reactions and antibody production. It is also known that immunological resistance to infection is primarily dependent on mechanisms of cell-mediated immunity (2), while the role played by the humoral immune response remains ill defined. Evidence now suggests that antibodies and activated T cells can interact and influence each other, affecting immunity and pathogenetic mechanisms in mycobacterial infections. In tuberculosis, immunosuppression has been associated with increased levels of antibodies against mycobacteria (9). Similarly, there is a negative correlation in leprosy between specific cell-mediated immunity and the levels of circulating antibodies. Generally, lepromatous patients have abnor- mally high levels of antibodies and weak cell-mediated immunity, whereas tuberculoid patients have low antibody levels and strong cell-mediated immunity (2). In recent years, several mycobacterial components that constitute major targets of antibody response in leprosy patients have been defined and characterized. Dominant carbohydrate-containing epitopes of Mycobacterium leprae are found in the specific phenolic I (PGL-I) and the cross- reactive lipoarabinomannan (4). The reactivity frequencies against these antigens in sera from lepromatous patients are relatively high in comparison with those in tuberculoid sera. In addition, some dominant antibody-reactive epitopes have been identified in proteins with apparent molecular masses of 28, 35, and 36 kDa (5, 13, 22). * Corresponding author. t Present address: Department of Microbiology, Colorado State University, Fort Collins, CO 80523. In a recent report, we were able to identify components in the short-term culture filtrates of Mycobacterium bovis that were markers of an appreciable humoral immune response in leprosy (19). The most reactive fractions were composed of a 28- to 30-kDa protein doublet, according to polyacrylamide gel electrophoresis, indicating that these proteins may act as markers in diagnosing this form of the disease. In the present study, the individual 28- and 30-kDa com- ponents of the 28- to 30-kDa doublet were resolved and identified as components of the BCG 85 complex (7, 25, 26), the mycobacterial family of fibronectin-binding proteins (1, 20). The antibody levels against these purified antigens were evaluated in sera from leprosy patients, household leprosy contacts, and control groups, suggesting a differential re- sponse to the two antigens. MATERIALS AND METHODS Sera. The test group consisted of 109 serum samples from leprosy patients registered for treatment at the Oswaldo Cruz Foundation, Rio de Janeiro, Brazil. All patients were clinically and histologically classified by the Ridley and Jopling scale and, on the basis of these results, divided into a polar lepromatous (LL) group consisting of 22 patients, a borderline lepromatous (BL) group (47 patients), an indeter- minate leprosy group (8 patients), and a borderline tubercu- loid leprosy group (32 patients). The majority of the patients had either been untreated or commenced chemotherapy; none of the patients had been treated for more than 2 years. Sera from 115 clinically healthy household contacts (HC) of leprosy patients were also studied; the majority of these were contacts of multibacillary patients. 2285 JOURNAL OF CLINICAL MICROBIOLOGY, Oct. 1991, p. 2285-2290 0095-1137/91/102285-06$02.00/0 Copyright © 1991, American Society for Microbiology on July 23, 2020 by guest http://jcm.asm.org/ Downloaded from