Identification of a novel subset of activation induced deaminase (AID)-dependent B-1 cells that mediate Initiation of Contact Sensitivity (37.10)

Abstract

Abstract Contact sensitivity (CS) to haptens is related to delayed type hypersensitivity (DTH) and is a well characterized prototype of T cell mediated inflammation. CS is additionally dependent on a parallel immune pathway. In response to sensitization, a population of B-1 cells produces antigen-specific IgM which mediates a rapid inflammatory response to hapten re-exposure. Interference with this pathway prevents the full development of the classic delayed response and is therefore termed the “CS-Initiation” pathway. The identity of the B-1 cell subset responsible for CS-Initiation is not known. Here, we show that CS-Initiation is dependent on activation induced deaminase (AID), an enzyme central to the process of somatic hypermutation (SHM). Using adoptive transfer experiments, we demonstrate that the defect is specific to B-1 cells as transfer of wild type B-1 cells reconstitutes CS-Initiation in deficient recipients. We went on to identify and characterize a unique subpopulation of B-1 cells in the spleens of sensitized mice that possess initiation activity. Detailed analysis of B cell receptor genes isolated from these cells revealed evidence of AID-mediated SHM. The sensitivity of CS-Initiation to very low amounts of hapten and the dependence on AID suggests that these cells are selected to generate antibodies capable of mediating CS-Initiation. This work funded by the Canadian Institutes of Health Research, the American Academy of Allergy, Asthma and Immunology and the National Institutes of Health.