GENE FAMILY USE AND SOMATIC MUTATION IN PRIMARY AND SECONDARY FLUORESCEIN-SPECIFIC IGM ANTIBODY-RESPONSES

A comparative analysis of the DNA sequences of primary and secondary I gM, fluorescein-specific antibodies was performed. These antibodies we re secreted by hybridomas generated following fusion of immunized BALB /c mouse lymphocytes and SP2/0 myeloma cells. Our results show that pr imary and secondary fluorescein-specific IgM antibodies use a variety of segments from the variable region of the immunoglobulin heavy chain locus (V-H), with members of the J558 and 7183 V-H gene families pred ominating in both populations. D regions from the DF116 and DSP2 famil ies were used exclusively in our primary antibody sample and predomina ted in the secondary response. In the primary antibodies, 15 out of 18 definable D regions were transcribed in reading frame one, but in the secondary antibodies the three reading frames were used stochasticall y. Secondary IgM antibodies showed a higher frequency of somatic mutat ion than their primary counterparts, but we could detect no evidence o f selection for mutations in the complementarity determining regions a s compared with the framework regions. It appears that fusion of secon dary cells, 3-6 days after immunization, is able to 'capture' the IgM- producing population of B cells at a stage in their development follow ing mutation but prior to antigenic selection.