Cloning, sequencing and expression of immunoglobulin variable regions of murine monoclonal antibodies specific for the p1.7 and p1.16 PorA protein loops of Neisseria meningitidis

The P1.7 and P1.16 epitopes on the PorA protein on the outer membrane of Neisseria meningitidis can induce protective antibodies upon vaccination. Structural analysis of antibodies to these targets can give information on the immune response induced by these epitopes and can reveal any structural similarities among the antibodies. To do so, we have isolated the immunoglobulin (Ig) variable genes from four mouse hybridomas expressing antibodies against the P1.7 and P1.16 epitopes. These V genes were successfully expressed as functional chimeric (ch) mouse/human IgG1 antibodies by subcloning them into expression vectors containing the constant genes of human heavy and light chains. Sequencing the two sets of V genes against P1.16 revealed a high degree of homology, similar to that previously published for P1.7 V genes. The close homology allowed us to interchange heavy and light chains between antibodies in some instances to construct new antibodies that bind the original antigen. This study demonstrates that the immune response in mice against the meningococcal PorA protein epitopes P1.7 as well as P1.16 is limited to few and very similar germline genes, and therefore the P1.7- and P1.16-specific antibodies share high degree of similarities amongst each other. These V genes were used to construct chimeric antibodies with conserved antigen-binding activity.