OPSONIC ANTIBODIES TO OUTER-MEMBRANE PROTEIN P2 OF NONENCAPSULATED HAEMOPHILUS-INFLUENZAE ARE STRAIN-SPECIFIC

The ability of monoclonal antibodies (MAbs) specific for variable and conserved epitopes of outer membrane protein (OMP) P2 (b,c) of nonenca psulated Haemophilus influenzae to promote opsonophagocytosis of this bacterium by human polymorphonuclear leucocytes (PMNs) was determined by flow cytometry. MAbs rendering PMNs fluorescent because of associat ion with fluorescein isothiocyanate-labelled bacteria were defined as stimulating opsonophagocytosis. Opsonophagocytosis was dependent on th e presence of both antibodies and complement. Of the 14 MAbs directed to the variable parts of OR IP P2 (L. van Alphen, P. Eijk, L. Geelen-v an den Broek, and J. Dankert, Infect. Immun. 59:247-252, 1991), 9 stim ulated opsonophagocytosis. Four of the five nonopsonophagocytic MAbs t hat were immunoglobulin G1 were unable to cause complement activation. The MAbs promoting opsonophagocytosis included MAbs specific for one or more OMP P2 antigenic variants of H. influenzae strains isolated fr om patients with chronic bronchitis during persistent infection. MAbs cross-reacting in enzyme-linked immunosorbent assays with nonrelated H . influenzae did not promote opsonophagocytosis of strains from other patients. Opsonophagocytosis was not observed in the presence of three MAbs reacting with OMP P2 epitopes common in H. influenzae. These res ults indicate that OMP P2-dependent opsonophagocytosis of nonencapsula ted H. influenzae is strictly strain specific.