Dominant cell wall proteins of Mycobacterium leprae recognized by monoclonal antibodies.

A cell wall fraction of Mycobacterium leprae has enhanced potency in activating immune T cells. By using a panel of monoclonal antibodies (MoAb), the dominant immunogen in this preparation was shown to be a complex of proteins of apparent molecular weight (Mr) 65 to 50 kD with a major antigen of 65 kD. Antigen capture assays supported the results of immunoblots and ELISA that this protein was concentrated in the cell wall. By varying the MoAb used as capture or tracer antibody, one of the three MoAb-defined epitopes on the 65 kD protein proved to be unique to M. leprae while the other two were shared by M. bovis (BCG) and M. tuberculosis. The cross-reactive epitope defined by MoAb L22 was present on a protein of Mr 12 kD as well as the 65 kD protein. The 12 kD protein was strongly radiolabelled with 125I and was immunoprecipitated by L22 but not by two other MoAb, L12 or L14. By contrast the higher molecular weight forms were only weakly precipitated by the three MoAb. Competitive inhibition assays with lepromatous leprosy sera demonstrated that the MoAb-defined epitopes were recognized by human B cells. The proteins bearing one of the cross-reactive determinants was purified from M. bovis (BCG) sonicate by affinity chromatography with MoAb L22 coupled to Sepharose 4B. This antigen fraction stimulated proliferation in peripheral blood mononuclear cells from BCG vaccinated, mantoux positive individuals indicating that the cell wall protein has cellular as well as humoral reactivity. The three MoAb defined epitopes are encoded by the DNA clone Y3178 recently isolated from M. leprae.