In vivo retroviral marking of antigen-specific B lymphocytes.

A major obstacle in the study of B lymphocyte development subsequent to immunization has been the paucity of distinctive phenotypic markers which might permit the separation and scrutiny of a mature antigen-experienced or memory cell population. To address this issue, we have introduced a recombinant non-replicating retrovirus into antigen-reactive lymph nodes in vivo using the expression of a reporter gene to monitor the trafficking, phenotype and persistence of retrovirus-marked B cells. Marked cells are first observed in the medullary cords where they proliferate for approximately 10 days prior to migration to the spleen. Up to half of the marked cells bear antigen-specific immunoglobulin receptors, but otherwise phenotypically resemble conventional B cells. The abundance and persistence of the marked cells suggest an association with the memory compartment. These experiments demonstrate a feasible approach for the identification and lineage analysis of antigen-responsive B cells, and suggest that the lymph node medulla supports a transient phase of post-antigenic B cell development associated with a long-lived antigen-specific B cell subset.