Antibody coating of bacteria is used to help diagnose lower respiratory tract infections; it is based on the postulation that invasive bacteria stimulate an immune response whereas colonizing bacteria do not. An aspirate sample is washed, pelleted, plated into shallow wells on microscope slides, and heat fixed, after which fluorescein-conjugated anti-human immunoglobulin is added with appropriate controls. Of patients with pneumonia, 54 to 73 per cent have antibody-coated bacteria compared with none to 2 per cent of the controls. There is no advantage in using specific immunoglobulin classes ( MeduriJ990).
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