HUMAN MONOCLONAL FAB FRAGMENTS SPECIFIC FOR VIRAL-ANTIGENS FROM COMBINATORIAL IGA LIBRARIES

Background: IgA constitutes the first line of immune defense, interacting with a variety of environmental antigens. Following infection with respiratory syncytial virus (RSV) individuals frequently exhibit elevated serum IgA titers specific for the virus. Previously combinatorial IgG libraries have successfully been used to clone such human antibody responses, Objectives: Here we evaluate the possibility of constructing combinatorial IgA libraries on the surface of filamentous phage to retrieve human viral-specific IgA Fab fragments. Study design: Bone marrow from an HIV-I seropositive donor was used as RNA source to construct combinatorial IgA kappa and lambda libraries of approximately 10(7) clones. Results: By affinity selection using an immobilized recombinant RSV FG protein, two unique IgA Fab fragments producing clones (AD5 and AD23) reactive with the selecting antigen were isolated. One of the Fab fragments was found to be specific for RSV F glycoprotein and bind with high apparent affinity (2 x 10(8) M(-1)). The other binds with lower affinity and exhibits cross-reactivity with other antigens. Conclusion. The strategy described, involving construction of combinatorial IgA libraries on the surface of filamentous phage, should be generally applicable to the investigation of both mucosal and systemic human IgA immune responses, and may become an important tool for evaluation of mucosal vaccine regimes.