Eizo Hayatsu

Interferon production during the course of Mycoplasma pneumoniae infection

In patients infected with Mycoplasma pneumoniae the development of interferon (IFN) was studied in nasopharyngeal secretions and sera. The production of IFN-gamma by lymphocytes was also investigated in response to M. pneumoniae antigen and mumps virus antigen. IFN-alpha was detected in 25 (61.0%) of 41 nasopharyngeal secretion samples and in 25 (59.5%) of 42 serum samples within 6 days after the onset of illness. IFN-alpha was significantly higher in nasopharyngeal secretions than in sera and a significant correlation was observed between the two. In most of the patients lymphocytes produced a larger amount of IFN-gamma in the convalescent stage than in the acute stage, when lymphocytes were stimulated with M. pneumoniae antigen. In some patients, however, lymphocytes did not produce IFN-gamma during the course of illness. Such lymphocytes, negative for IFN-gamma production in response to M. pneumoniae, produced IFN-gamma after the depletion of macrophages, and readdition of macrophages suppressed the production of IFN-gamma by lymphocytes. When lymphocytes were stimulated with heterogeneous antigen (mumps virus), they produced no IFN or a small amount of IFN in the acute stage of M. pneumoniae infection, and IFN production increased in the convalescent stage. Different mechanisms seem to work for homogeneous and heterogeneous antigens in the suppression of IFN production in M. pneumoniae infection.

Acquired Immunity to Mycoplasma pneumoniae Pneumonia in Hamsters

An inactivated Mycoplasma pneumoniae vaccine was prepared from a culture in a liquid medium supplemented with water extract of egg yolk. Vaccinated Syrian hamsters were exposed to virulent M. pneumoniae aerosol and were examined for the retention of mycoplasmas and for histopathological changes in the respiratory tracts. When a vaccine prepared with strain FH was administered intramuscularly or by inhalation in aerosol, no significant resistance was shown with respect to mycoplasma proliferation. An increased resistance, however, was observed when an aluminium phosphate‐adsorbed vaccine, and when a plain vaccine (although to a lesser degree) prepared with hamster 24‐passaged strain FH, was administered intramuscularly. Histopathologically, lung lesions were markedly suppressed in groups showing high resistance. A correlation between the serum antibody titer and the resistance to infection was observed. Hamsters which received a hyperimmune rabbit antiserum intracordally showed a high resistance to M. pneumoniae infection. The suppression of histopathological changes also coincided with high complement‐fixing antibody titers of either actively or passively immunized hamster serum. The results suggest that humoral immunity plays an important role in resistance to M. pneumoniae pneumonia in hamsters.

Immunological Responses of Hamsters in the Acquired Immune State to Mycoplasma pneumoniae Infection

Protective effects of vaccination of hamsters against Mycoplasma pneumoniae infection, evaluated according to the recovery of mycoplasmas and histopathological changes in the respiratory tract after challenge infection, persisted for at least 6 months after the final vaccination. Serum antibody levels reached a maximum in the second week after the last vaccination and decreased markedly between the first and the third months, but increased again in sera obtained from animals given booster injections. Metabolism‐inhibiting antibodies were detected in bronchial washings of animals showing high resistance obtained by vaccinal or passive immunization. Antiserum transfer was also effective for protection but cell‐mediated immune responses were not demonstrated in any animals up to 6 months after the vaccination. Even after 10 months, suppression of both mycoplasmal proliferation and lung lesions was apparent, and a single dose of the vaccine induced a significant booster effect. These findings suggest that (1) humoral immunity is more important than cell‐mediated immunity in resistance of hamsters to M. pneumoniae pneumonia, and (2) the antibody secreted in the respiratory tract may be involved in the local defense mechanisms.

Role of Humoral Antibodies in Resistance to Mycoplasma pneumoniae Pneumonia in Hamsters

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.

Immunogenicity and Protective Effect of Hemolysis Mutants of Mycoplasma pneumoniae

Two attenuated strains of Mycoplasma pneumoniae, P24‐S1 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% 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.

Characterization and Pathogenicity of Hemolysis Mutants of Mycoplasma pneumoniae

Hemolysis mutants were produced by treating Mycoplasma pneumoniae FH‐P24 strain with N‐methyl‐N‐nitro‐nitrosoguanidine and were classified into three different groups. The first group of mutants, strains P24‐L1, L2, and L11, showed wide and clear hemolytic zones. Their attachment ability to erythrocytes of various animals and to hamster lung cells were the same as those of the parent strain. The second group, strain P24‐S1, showed non‐hemolysis and non‐hemadsorption, but retained the attachment ability to lung cells, although not to erythrocytes. The third group, strain P24‐S11, was non‐hemolytic, had completely lost the attaching ability, and did not proliferate in vivo. Strains in the first group produced significant microscopic pneumonic lesions in hamsters while strain P24‐S1 produced milder lung lesions. Strain P24‐S11 did not cause any lung lesions, and organisms were not recovered from the lungs of hamsters. The attachment of M. pneumoniae to respiratory epithelium as a cause of infection and the existence of a relationship between the hemolytic abilities of the organisms and histopathogenicity in the hamster lung tissue were further supported by the present data.

Suppressive Effect of Macrophages on Interferon-γ Production by Human Peripheral Lymphocytes Stimulated with Mycoplasma pneumoniae

Production of interferon (IFN)‐γ was investigated in human peripheral lymphocytes stimulated with Mycoplasma pneumoniae. Lymphocytes obtained from non‐immune individuals produced no IFN. IFN‐γ was produced by T cells obtained from immune individuals, and the helper/inducer T cells produced two‐ to sixfold higher titer of IFN‐γ than the suppressor/cytotoxic T cells. The addition of macrophages in T cell cultures suppressed the production of IFN‐γ; this differs from the previous result wherein the addition of macrophages enhanced the production of IFN‐γ, when stimulated with mumps virus or measles virus.