Fluorescent antibody technics have been applied to various fields of medicine for
demonstrating the presence and localization of antigens in tissues and cells and for
detecting antibodies to these antigens. In mycobacterial diseases, however, this technic
brought little benefit, altholigh several trials were reported by some investigators. This
may be due to a broad spectrum of common antigenicity among various strains of
mycobacteria, and therefore due to difficulty in preparing specific antigen for
serodiagnosis.
Since large quantities of Mycobacterium leprae made available from infected armadillo
tissued, there have been many evidences that protein antigens specific to this bacillus
exist. However, nobody has so far succeeded in using specific antigen for the
serodiagnosis of leprosy. In 1970 (1), Ⅰ reported the presence of protein antigens in
crude extract of leprosy nodules, using immuno-electrophoretic technics. It was the first
result of my study on active substances in lepromin. Leprosy nodule extract (NE) gave
single precipitation line against rabbit antisera to lepromatous tissue, NE and NEPR
(purified protein of NE), while no reaction against the antiserum to M. leprae purified by
trypsin digestion. This fact suggests the most of protein antigen was lost during the
purification. On the other hand, normal skin extract gave no precipitation against these
antisera. Therefore, it is obvious that NE contains protein antigen specific to
lepromatous tissues.
Then, all of the components present in leprosy nodule extract were fractionated by
starch-block zone-electrophoresis and gel-filtration through Septadex G200 column or
CMC-column chromatography. The last procedure allowed to separate one fraction
consisted mainly of polysaccharide, while the other fractions consisted of proteins. Ten
micrograms of each autoclaves fraction were used for skin test with leprosy patients, in
order to know the distribution of skin-reacting antigen in these fractions. The result is
shown in Table 1. Only F4G2, NEPR and NEG2 showed positive skin reaction, with a
diameter larger than 10 mm, in borderline and tuberculoid crises, while negative in
lepromatous. F4G2 was later found to contain the same antigen as NEG2. Therefore, we
could fine at least two protein antigens, NEPR and NEG2, causing Fernandez-type skin
reaction (2). NEPR had higher molecular weight than that of NEG2. NEPR was a good
immunogen in rabbits, while NEG2 was not. Therefore, antigenic property of NEG2 was
not known.
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