The levels and bactericidal capacity of antibodies directed against the UspA1 and UspA2 outer membrane proteins of Moraxella (Branhamella) catarrhalis in adults and children

The UspA1 and UspA2 proteins from Moraxella catarrhalis share antigenic epi topes and are promising vaccine candidates, In this study, the levels and b actericidal activities of antibodies in sera from healthy adults and childr en toward UspA1 and UspA2 from the O35E strain were measured. Human sera co ntained antibodies to both proteins, and the levels of immunoglobulin Cr (I gG) antibodies were age dependent, Adult sera had significantly higher tite rs of IgG than child sera (P < 0.01), The IgG3 titers to the UspA proteins were higher than the IgG1 titers in the adults' sera, while the IgG1 titers were higher than the IgG3 titers in the children's sera (P < 0.05). The Ig G antibodies in the sera from 2-month-old children appeared to be maternall y derived, since the mean titer was significantly higher than that in sera from 6- to 7-month-old children (P < 0.05), Serum IgA antibodies to both Us pA1 and UspA2 were low during the first 7 months of age but thereafter grad ually increased along with the Ige titers, Analysis of sera absorbed with U spA1 or UspA2 showed that the antibodies to UspA1 and UspA2 were cross-reac tive with each other and associated with serum bactericidal activity. Exami nation of affinity-purified human antibodies confirmed that naturally acqui red antibodies to UspA1 and UspA2 were bactericidal and cross-reactive. The se results support using UspA1 and UspA2 in a vaccine to prevent M. catarrh alis infections.