Two hundred fifty strains of Mycoplasma pneumoniae isolated during the past 20 years in Japan were classified into two groups (I and II) based upon different PCR-restriction fragment length polymorphism patterns of their P1 cytadhesin genes. Clear shifts between the M. pneumoniae groups were observed but did not appear to be correlated with M. pneumoniae epidemic cycles. Patients' sera showed relatively higher levels of antiadhesin antibodies to M. pneumoniae strains homologous with the infecting strain.

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

Two attenuated strains of Mycoplasma pneumoniae, P24-S 1 and P24-S11, were tested for their ability as a live vaccine to confer on hamsters immune resistance against challenge infection with a virulent strain of M. pneumoniae, FH-P24. Fifty percent protection was obtained by vaccination with the P24-S1 strain administered once or twice.In contrast, only 10°0 of the animals were protected by the P24-S11 vaccine even when it was given three times. Vaccination with the P24-S1 strain resulted in higher humoral and cellular immune responses than the P24-S11 did.These results suggest that the P24-S1 strain has the primary qualities a vaccine which may be used for protection against human mycoplasmal infection.

SPF-BALB/c mice in which Mycoplasma pneumoniae cell proliferation accompanied by immunological responses had been confirmed, were immunized with live vaccines or with hyperimmune sera of M. pneumoniae FH-P24 and its mutant strains (P24-S1, P24-S11), were then assayed for infection-protection. Eight weeks after the last vaccination, 70 percent protection was obtained by inoculation once or twice with live FH-P24 and P24-S1 vaccines, respectively. After 12 weeks, 80% protection was achieved by FH-P24 and 60% by P24-S1 live vaccine, while protectivity was not obtained by P24-S11 live vaccine. In case of passively immunized mice, IgG antibody titers and protective effect were not always found to be parallel. Namely, mice which were passively immunized with anti-FH-P24 serum, showed only 20% protection. However to get the above results, it was necessary that the anti-mutant strain serum be ten times higher than anti-FH-P24 serum in IgG titer. In the immunoblot analysis, sera from patients infected with M. pneumoniae immunoblotted the 168-KDa (P1 protein) and the 85-KDa protein of FH-P24 and P24-S1, but not the 85-KDa protein of P24-S11.