Anti-mycobacterial antibodies in saliva

Abstract

Modified techniques for the fluorescent leprosy antibody absorption (FLA-ABS) test and the enzyme-linked immunosorbent assay (ELISA) using phenolic glycolipid-I (PG) antigen of M. leprae were employed for detecting anti-M. leprae antibodies in sera and saliva from the patients with leprosy, household contacts and inhabitants in leprosy endemic areas. The FLA-ABS test with saliva was positive in 20 (58.8%) of the 34 household contacts, 92 (39%) of the 236 schoolchildren and 37 (38.1%) of the 97 adults who had social contacts with leprosy, but negative in the 23 patients with pulmonary tuberculosis. Serological specificity of salivary anti-M. leprae antibodies detected in the specimens of saliva from the schoolchildren was checked by cross-reactions and additional absorption tests. Only 7 out of the 55 specimens of saliva showing a positive FLA-ABS test were cross-reactive with some species of mycobacteria. Positive reactions against M. leprae were not influenced at all by additional absorptions with cross-reacting mycobacteria, but became negative after an additional absorption with M. leprae. Therefore, the modified technique of FLA-ABS test was found specific to M. leprae and useful for detecting subclinical leprosy infection. The PG-ELISA activity was most frequently found in the serum and salivary IgA from the patients with leprosy, the percentage of positive reactions in saliva being comparable to that of FLA-ABS test. The PG-ELISA using anti-IgA-enzyme conjugate was negative in the specimens of saliva from the patients with tuberculosis and the schoolchildren who had no suspicious symptom nor FLA-ABS reactivity, but was positive in 3 (11.1%) of the 27 specimens of saliva from the schoolchildren who had suspicious symptoms and/or FLA-ABS reactivity and in 17 (17.5%) of the 97 specimens of saliva from the adults who had social contacts with leprosy. Therefore, the PG-ELISA with saliva was also found specific to M. leprae and useful for detecting the secretory type of anti-PG antibodies. A significant difference in the percentage of positive reactions between FLA-ABS and PG-ELISA was discussed from a point of view concerning specific epitopes of M. leprae.