Development of Monoclonal-antibody-ELISA, -DOT-BLOT and -DIP-STICK Immunoassays for Humicola lanuginosa in Rice

Abstract

Monoclonal antibodies (MAbs) were raised against Humicola lanuginosa, a thermophilic, saprophytic fungus that is commonly isolated from freshly harvested rice grains in Indonesia. Mice were immunized by direct injection into the peritoneum, without prior concentration, of fresh cell-free surface washings from a solid agar slant culture. Hybridoma supernatants were screened by ELISA using wells coated with a dilution of the immunogen. From one fusion 403 hybridoma clones were obtained yielding 52 cell lines secreting antibodies positive for H. lanuginosa. Twelve cell lines were re-cloned, grown in bulk and tested against other storage fungi. Most of the MAbs raised were IgM antibodies that cross-reacted with several of the storage fungi and/or uninfected rice grains. However, the IgM antibody EC6 did not recognize antigens from rice grains and cross-reacted strongly with only one other test fungus, Penicillium variabile, and partially with two others. This MAb was used to develop a highly sensitive DIP-STICK immunoassay to detect the fungus in infected grains. These assays are simple to perform, require no equipment and are suitable for field use by untrained workers.