In 1890,Emil von Behring and Shibasaburo Kitasato demonstrated the efficacy of serum transfer at conferring infection resistance-a process now known as "passive immunity." The researchers isolated serum from animals that had recovered from infection with the diphtheria bacilli and subsequently injected the serum into other healthy animals.This procedure conferred specific resistance against the pathologic effects of diphtheria infection in the recipient animals.Which of the following immune phenomena were primarily responsible for these effects?

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The serum from infected animals contains diphtheria-specific antibodies.Some of these antibodies can bind to and neutralize diphtheria toxin,reducing symptoms of infection,whereas others interact with the bacilli themselves,inducing bacterial death by phagocytosis and complement fixation.Antibodies have a half-life of several weeks in the circulation,and therefore promote short-term disease resistance and immunity.No B cell or T cell would have been transferred with the serum,which is a cell-free fraction of blood.It is unlikely that there are inflammatory cytokines in the serum donor,because it had already recovered from infection,and cytokines alone would not impart resistance to infection.Serum transfer should not provide any complement components not already present in the recipient.Although it is possible that the foreign serum elicited an immune response to allelic differences in the transferred serum proteins,this should not impart specific resistance to diphtheria.

In 1890,Emil Von Behring and Shibasaburo Kitasato Demonstrated the Efficacy