Immunoglobulin G subclass-specific antileishmanial antibody responses in indian Kala-Azar and post-Kala-Azar dermal leishmaniasis

Antileishmanial antibody responses in the sera of Indian kala-azar (KA) and post-KA dermal leishmaniasis (PKADL) patients were analyzed by enzyme-linked immunosorbent assay (ELISA) and immunoblot experiments using immunoglobulin G (IgG) class- and subclass-specific reagents. All sera showed antileishmanial reactivities in IgG ELISA which followed the order IgG1 > IgG2 > IgG3, with very little IgG4. Immunoblot analysis with IgG class-specific reagents revealed variable patterns of reactivity by KA and PKADL sera, although certain common bands around the 60- to 63-kDa and 28-kDa regions were discernible. Sera from antimony-unresponsive KA cases, on the other hand, strongly recognized two bands at around 20 to 22 kDa, in addition to other bands in the high-molecular-mass region. Further analysis showed that the 28-kDa band was preferentially recognized by the IgG2 isotype, while 20- to 22-kDa and 60- to 63-kDa bands were recognized by the IgG1 isotype. Antibodies belonging to the IgG3 isotype reacted to antigens primarily in the region of 14 to 34 kDa and persisted in patients even several months after cure. Immunoblot studies also revealed the presence of a nonspecific band which arose as a result of binding bet veen a 66-kDa leishmanial antigen and streptavidin. Finally, the results presented in this study suggest that certain leishmanial antigens preferentially stimulate the synthesis of a particular IgG subclass(es), depending on the nature of such antigens or their epitopes.