Suppression of human PMN bactericidal activity by human IgA paraproteins.

IgA paraproteins which have previously been shown to suppress neutrophil chemotaxis were found to suppress neutrophil bactericidal activity in a concentration dependent manner. This inhibition was cell directed, dependent on the Fc portion of the IgA, and lost after reduction and alkylation which resulted in conversion of polymeric to monomeric IgA. IgA suppression of bactericial activity was not due to interference with cell metabolism or membrane fluidity as evidenced by a lack of effect on chemiluminescence or Con-A cap formation. Further tests demonstrated that the presence of IgA paraproteins inhibited PMN ingestion of IgG coated latex particles which could account for their effect on PMN bactericidal activity.