Immunization of mice with P6 of nontypeable Haemophilus influenzae: kinetics of the antibody response and IgG subclasses

The kinetics of the anti-P6 antibody response was characterized in three st rains of mice of different haplotypes (Balb/c; H-2(d), C3H/H; H-2(k), SJL/J ; H-2(s)). Anti-P6 antibodies were measured on a weekly basis by enzyme-lin ked immunosorbent assay (ELISA), The primary response peaked 2 or 3 weeks a fter the initial injection with 40 mu g of purified P6. The response remain ed at a plateau for 8-10 weeks. A maximum titer of 1:1,638,400 was attained and then steadily declined. To study the ability of P6 to generate a recal l response, we opted to boost the vaccinated mice with a known subimmunogen ic dose of live nontypeable Haemophilus influenzne (NTHI) bacteria. After t he anti-P6 antibody titers in the primed animals had stayed at baseline lev els for 2 weeks, the mice were injected intraperitonealy with 10(8) cfu of NTHI in sterile saline. This challenge with live NTHI bacteria induced a ve ry rapid and strong secondary antibody response in all mice. Finally, we de monstrated that these murine anti-P6 sera were 100% bactericidal against th ree strains of NTHI when tested in a complement dependant bactericidal assa y. (C) 1999 Elsevier Science Ltd. All rights reserved.