218 Effect of Tissue Site and Antigen on Antibody Expression

Multiple genes code for the variable (V) x and constant (C) regions of immunogiobulin polypeptides. In addition to the large number of V genes which code for antibody combining sites, the murine heavy-chain locus has as many as 10 C (.CH) genes which specify molecules with different effector functions. As B cells have the potential to respond to an antigen by producing antibodies with a variety of V and C regions, it is of basic interest to study factors that affect the relative frequencies of certain V region clonotypes within the diverse repertoire, and that determine which Cn isotypes are produced by a B-cell clone after antigen stimulation. We have used the cloning assay of Klinman (1) to study both aspects of B-cell differentiation by examining the influence of lymphoid organ site and antigen load on the expression of V and C regions. At the level of V region expression, questions about the B-cell repertoire include (a) do various lymphoid tissues have the same frequency of precursors specific for an antigenic determinant, (b) does the repertoire of cells bearing different V regions specific for an antigen vary among tissues, and (c) how do encounters with antigen change the frequency and repertoire of affected B cells? Using a probe for the V region idiotype, the number of cells expressing a particular V region (clonotype) can be assessed relative to the total number of B cells specific for that antigen. Thus both the total number of precursors and the size of a subset within that population can be compared among lymphoid compartments before and after antigen stimulation.