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? Pathogen-specific B and T cells from the original infected animals triggered a robust immune response after re-exposure to diphtheria antigens in the recipient animal. Inflammatory cytokines in the transferred serum increased the strength and efficacy of innate immune system activity. Diphtheria-specific antibodies in the transferred serum neutralized bacillus toxins and promoted bacterial elimination by innate effector cells. Serum complement proteins in the transfer directly promoted bacterial cell lysis and phagocytosis. The recipient animal s immune response to the foreign serum further activated host immune system function, allowing greater response to the bacillus infection.