Persistence of community-acquired respiratory distress syndrome toxin-producing Mycoplasma pneumoniae in refractory asthma

Abstract

Background: The role of Mycoplasma pneumoniae (Mp) in the initiation and persistence of asthma remains elusive. Mp community-acquired respiratory distress syndrome toxin (CARDS Tx) is a unique virulence factor that induces an intense lymphocytic response and exacerbates asthma in animal models. We sought to determine the incidence of Mp infection and the presence of CARDS Tx in subjects with refractory asthma (RA).

Methods: We conducted a prospective observational study in 64 subjects with RA. Respiratory secretions (sputum, nasal lavage, and throat swab) and blood were analyzed for the presence of CARDS Tx and P1 adhesin (P1) DNA by polymerase chain reaction (PCR), and CARDS Tx by antigen capture. Serum IgM and IgG antibodies to CARDS Tx were determined by enzyme-linked immunosorbent assay (ELISA).

Results: Thirty-three of 64 subjects (52%) tested positive for Mp: 29 of 33 by CARDS Tx vs 10 of 33 by P1 assays. Ten subjects followed longitudinally for up to 633 days tested persistently positive for Mp. There were no significant differences in Mp-specific IgG responses between Mp-positive and Mp-negative groups. Eight of 10 subjects who tested persistently positive failed to mount a substantial IgG response to CARDS Tx, and up to 8 weeks of clarithromycin failed to eradicate Mp in five subjects.

Conclusions: Subjects with RA may be chronically infected with Mp. PCR for CARDS Tx appears to be the most sensitive method of identifying Mp infection. Despite the persistence of Mp in subjects with RA, some subjects failed to mount an IgG response, and macrolide therapy was insufficient to eradicate Mp.

Figure 1.

CARDS Tx PCR levels and serologic responses in 10 subjects with persistent Mycoplasma pneumoniae infection. A, PCR. B, CARDS Tx IgM. C, IgG titers. Each line represents an individual case. The index case is shown in bold dashed lines. CARDS Tx genome levels graphed at 10⁻¹ genomes represent samples that were below the detectable limits for the assay. CARDS Tx = community-acquired respiratory distress syndrome toxin; OD = optical density; PCR = polymerase chain reaction.

Figure 2.

Serologic responses to CARDS Tx and P1 adhesin. Serum IgG and IgM directed against CARDS Tx and P1 adhesin were analyzed by enzyme-linked immunosorbent assay at the initial visit for all subjects. Data are expressed as OD 405. See Figure 1 legend for expansion of abbreviations.

Figure 3.

Sputum sample. A, Stained with rabbit anti-CARDS TX polyclonal antibodies (left) or control rabbit antibody (right) (original magnification × 60). B, Stained with mouse anti-P1 monoclonal antibody (left) or control mouse antibody (right) (original magnification × 60). Both techniques demonstrated mycoplasmas associated with mononuclear cells in the sputum of a subject (shown in bold dashed lines in Figure 1) who had been treated with 8 weeks of macrolide therapy.