IgA proteases are extracellular metalloendopeptidases released by bacteria that selectively cleave IgA at the hinge region, allowing for increased bacterial colonization of mucosal surfaces. We recently identified IgA1 and IgA2 proteases in the Mannheimia haemolytica secretome. IgA-specific protease of M. haemolytica, the main bacterial causative agent of Bovine Respiratory Disease (BRD), is a possible virulence factor or target of mucosal immunity to increase the efficacy of vaccines against BRD. In order to study this, both IgA protease genes were cloned, and sequence analysis revealed that the proteins have multiple domains viz., 1) IgA protease, 2) pertactin, and 3) autotransporter. The whole protein has a calculated molecular weight of 164kDa, whereas IgA1, pertactin, and autotransporter have molecular weights of 70 kDa, 25 kDa, and 64 kDa, respectively. Recombinant forms of each protein has been purified. In assays to determine the IgA-specific protease activity of M. haemolytica, purified bovine IgA was incubated with concentrated M. haemolytica culture supernatant or rIgA1. SDS-PAGE and western blot analysis demonstrated IgA-specific protease activity in the presence of ZnCl2. In supernatant, which resulted in the release of an approximately 37 kDa product. The identity of the cleavage product was confirmed as a portion of IgA by LC-MS/MS spectrometry. Convalescent bovine sera with naturally high anti-M. haemolytica antibody titers were tested for anti-IgA protease components in ELISA, where rIgA1, rIgA2 and r-pertactin were used as ligands. Data from this study showed that there were high anti-IgA1 & IgA2 protease antibodies and low anti-pertactin antibodies, confirming the immunogenic nature of these proteins. Highly pure recombinant forms of IgA1, IgA2, pertactin and autotransporter will be used in immunization studies of mice. Results of immunization of mice with rIgA1 & r-pertactin will be addressed.