Two major
proteins from Mycobacterium bovis BCG culture filtrates with molecular masses of 28 kDa (P28) and 30 kDa (P30), 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 P28 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.