Cloning of microbial epitopes relevant for T- and B-cells

This review summarises, and illustrates, the technology that is available for the molecular cloning and precise identification of T-cell and B-cell epitopes, particularly those of bacteria and parasites. Methods include: selective cloning following subtractive hybridization of nucleic acids; selective screening of expression libraries; analysis of subcloned "epitope libraries" or "deletion constructs"; scanning of multiple synthetic peptides, and computer enhanced prediction. The direct sequencing of polymerase chain reaction products allows the rapid analysis of epitope heterogeneity occurring among natural populations. Multiple epitopes can be assembled either by synthesis or by the expression of polymeric epitope-bearing peptides. Prospects for probing expression libraries with T-cells are bleak due to the complexities of antigen processing, presentation and T-cell recognition in vitro. Elucidation of the enzymic steps involved in processing, resolution of peptide/MHC II co-crystals, and pairing of a large number of known epitopes with their functional restriction elements will significantly improve the ability to predict T-cell epitopes.