Seventy

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Golden Syrian hamsters adoptively immunized with hyperimmune Mycoplasma pneumoniae rabbit antiserum, immunoglobulin (Ig) M-rich (IgM) fraction, IgG-rich (IgG) fraction, antiserum absorbed with either killed M. pneumoniae or killed Staphylococcus aureus organisms, or antiserum treated with 2-mercaptoethanol (2-ME) were examined for resistance against aerosol infection with virulent M. pneumoniae. Significant resistance to the establishment of infection in the respiratory tract was shown in hamsters pretreated with the untreated antiserum, IgG fraction or 2-ME-treated antiserum, whereas animals pretreated with the IgM fraction and the antisera absorbed with M. pneumoniae or S. aureus organisms were not significantly resistant. Histopathologically, lung lesions were markedly suppressed in animals with high resistance, but were typically pneumonic in animals with low or no resistance. The efficacy of adoptively administered serum preparations was closely related to their antibody titers. The results indicate that humoral antibody plays an important role in protection against experimental M. pneumoniae pneumonia in hamsters, although the participation of the cell-mediated immune response was not determined.We (8) reported earlier that an inactivated adjuvant vaccine prepared with Mycoplasma pneumoniae strain FH-P24, passaged 24 times in vivo, induced a high level of serum antibody in hamsters and showed a very high protective potency. The results support those of Chanock and his co-workers (2, 11, 13) and McCormick et al (10), who stated that resistance of humans to M. pneumoniae pneumonia was correlated with the presence of naturally acquired or vaccine-induced antibody in serum. In our previous study, also, resistance against M. pneumoniae infection in hamsters corresponded to serum antibody titers, especially those of complement-fixing (CF) antibodies (8).In the present study, we analyzed the role of the humoral immune factor by adoptive immunization with the antiserum, its immunoglobulin (Ig) M-rich (IgM) and IgG-rich (IgG) fractions, the antiserum absorbed with killed Staphylococcus 585

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