The mechanisms of antibody generation in the llama

The llama is able to generate a unique class of antibody. The heavy chain immunoglobulins consist only of two heavy chain polypeptides and bind antigen specifically through single protein domains. Although the mechanisms by which such an antibody interacts with antigen has been studied at some length the manner in which the heavy chain antibody is generated within the llama is unknown. In this study a number of components of the llama immune system have been characterised. The isolation of genes encoding the variable domain of the heavy chain antibody indicates that specific genetic elements within the llama genome are responsible for the generation of the heavy chain antibody. The discovery of constant region genes that encode the heavy chain antibody provides an explanation for the absence of a major immunoglobulin domain from the final, secreted gene product. The lack of this domain within the expressed antibody is believed to be the result of a single nucleotide splice site mutation. In order to investigate the process of llama antibody generation further additional components of the llama immune system, the recombination activating genes (rag) were isolated. One such llama rag gene (rag-i) was cloned, expressed and utilised in an in vitro assay system to investigate recombination events taking place during antibody generation. This assay involved the use of specific signal sequences derived from variable domain gene sequence data and represents, to our knowledge, the first examination of non-murine RAG activity. Through the use of this system distinct differences between llama and mouse recombination signal sequences (RSSs) were uncovered. These differences, located within a specific region of the RSS known as the coding flank, may play an important role in llama antibody generation. These results have led to the proposal of a number of models for the mechanisms involved in llama antibody generation.