Role of Immunity in the Clearance of Bacteremia Due to Haemophilus influenzae

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Abstract
The role of antibodies to capsular and somatic antigens in the clearance of Haemophilus infiuenzae was investigated by active and passive immunization. The clearance index (k) and the proportion of strain b organisms cleared 30 min after intravenous administration (ΔY30) were greater in eight-week-old actively immunized rats (k = 0.693, ΔY30 = 4.07) than in nonimmune animals (k = 0.075, ΔY30 = 0.95) (P < 0.025 for all); however, clearance correlated imprecisely with titers of bactericidal or anticapsular antibody. In three-week-old rats, intranasal immunization with strain b or U significantly increased (P < 0.005) the rate of clearance of strains band U. Passive immunization with antibodies to somatic or capsular antigens significantly increased the rate of clearance (P < 0.001) and the proportion of bacteria cleared (P < 0.05) with all test strains. The increased clearance associated with passive immunization correlated with increased splenic uptake of 32P-labeled H. influenzae (r =0.83, P < 0.025). Analysis of the disappearance of viable organisms and bacterial 32P suggested that bacteriolysis of H. influenzae did not occur during clearance of the bacteremia. Either antibody to capsular antigen or antibody to somatic antigen, administered or evoked in rats, accelerates intravenous clearance of H. influenzae by promotion of reticuloendothelial phagocytosis.