We have constructed chimaeric (ch) mouse/human antibodies with identical binding regions isolated from the V-genes of two mouse parent hybridoma cell lines, with specificity against the P1.7 and P1.16 epitopes on the outer-membrane protein PorA on meningococci. The chimaeric antibodies can be used to analyse relationships between specificity, binding activity (avidity and kinetics), isotype (antibody class and antibody subclass) and in vitro anti-bacterial activity of meningococcal antibodies. The antibody sets represented the human isotypes IgG1, IgG3 and IgM, which dominate during immune response against protein antigens. The binding activities were quite similar for all these isotypes, surprisingly also for the pentameric IgM. Interestingly, monomeric IgM, prepared from pentameric IgM by partially reduction and alkylation, had similar binding activities as the original pentameric IgM. Regarding in vitro anti-bacterial activity, chIgG1 was superior in SBA (serum bactericidal activity) compared with chIgG3, while chIgG3 was more efficient in OP (opsonophagocytosis; measured by flow cytometry) than chIgG1. ChIgM showed slightly higher SBA than chIgG1 on molar basis, and much higher OP than chIgG3 and chIgG1. A lower concentration of antibodies was needed against the P1.16 than against the P1.7 epitope to induce SBA, but this was not the case for OP.

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