Mycoplasma pneumoniae-specific antibody-secreting cells (ASCs) in the peripheral blond were enumerated with an enzyme-linked immunospot assay in 12 children with mycoplasma pneumonia. Those cells were detected in the acute phases and declined in number in the convalescent stage. The maximum numbers of M. pneumoniae-specific ASCs ranged from 0 to 478 for immunoglobulin G (IgG), 13 to 1,992 for IgM, and 0 to 53 for IgA per 106 peripheral blood mononuclear cells, whereas the total numbers (i.e., including both specific and nonspecific) of immunoglobulin-secreting cells (IgSCs) were as high as 4,000 for both IgG and IgM and 1,000 for IgA per 106 peripheral blood mononuclear cells. Such a great increase in the numbers of total IgSCs in comparison with that in M. pneumoniae-specific ASCs suggests that the majority of the IgSC increase in the course of mycoplasmal infection was nonspecific to M. pneumoniae. The serum level of M. pneumoniae antibody measured by enzyme-linked immunosorbent assay remained high in the convalescent phase, while the number of specific ASCs decreased. Whereas this observation may be explained by declined degeneration or consumption of the antibody in the convalescent phase, it may be suggestive of the source of M. pneumoniae antibody other than ASCs in the peripheral blood.
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