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. 2001 Sep;39(9):3425–3426. doi: 10.1128/JCM.39.9.3425-3426.2001

Labsystems Enzyme Immunoassay for Chlamydia pneumoniae Also Detects Chlamydia psittaci Infections

Kristoffer Strålin 1,2,*, Hans Fredlund 1,2, Per Olcén 1,2
PMCID: PMC88366  PMID: 11558474

In a recent article, Bas and collaborators compared different serological methods to detect chlamydial antibodies in patients with Chlamydia trachomatis infections and healthy blood donors (1). Using the Labsystems enzyme immunoassay (EIA) for C. pneumoniae, no cross-reaction between C. trachomatis and C. pneumoniae was found. However, Gnarpe and collaborators recently showed cross-reactions between C. trachomatis and C. pneumoniae, when the Labsystems EIA for C. pneumoniae was used on sera containing high titers of C. trachomatis antibodies documented by the microimmunofluorescence (MIF) test (2). A broader cross-reactivity between the different chlamydial species was suspected. The Labsystems EIA test has previously been shown to have high sensitivity and specificity in the diagnosis of acute infections caused by C. pneumoniae during an epidemic of C. pneumoniae (3).

To examine the Labsystems EIA test for C. pneumoniae more extensively, we tested it on paired sera, taken from 43 patients for etiological diagnosis of pneumonia. The immunoglobulin G (IgG) and IgM antibody results for C. pneumoniae, C. psittaci, and C. trachomatis had previously been documented by the MIF tests, and IgG and IgM antibodies were now determined by the Labsystems EIA for C. pneumoniae. Of seven patients who were positive by the MIF test for C. pneumoniae, only three were positive by the EIA for C. pneumoniae, while five out of five patients who were positive by the MIF test for C. psittaci were positive by the EIA for C. pneumoniae. One patient with positive MIF test results for both C. pneumoniae and C. psittaci also tested positive for C. pneumoniae by the EIA. Sera from the remaining 30 patients, who showed no significant IgG or IgM antibody changes with the MIF test, also produced negative results with the EIA.

Because infections caused by C. pneumoniae and C. psittaci have important epidemiological differences, it is important to make a correct etiological diagnosis. The study of Gnarpe and collaborators and the present study indicate that cross-reactions between the chlamydial species occur when the Labsystems EIA for C. pneumoniae is used. The EIA could be used for the purpose of screening for chlamydial infections, but in nonepidemic situations we suggest that a method that differentiates between the chlamydial species, such as the MIF test, should be used directly (or, alternatively, as a second step after a screen with the EIA).

REFERENCES

  • 1.Bas S, Muzzin P, Ninet B, Bornand J E, Scieux C, Vischer T L. Chlamydial serology: comparative diagnostic value of immunoblotting, microimmunofluorescence test, and immunoassays using different recombinant proteins as antigens. J Clin Microbiol. 2001;39:1368–1377. doi: 10.1128/JCM.39.4.1368-1377.2001. [DOI] [PMC free article] [PubMed] [Google Scholar]
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J Clin Microbiol. 2001 Sep;39(9):3425–3426. doi: 10.1128/JCM.39.9.3425-3426.2001

AUTHORS' REPLY

S Bas 1, T L Vischer 1

In our study (1-1), we compared two different methods of serodiagnosis for Chlamydia pneumoniae infections (an enzyme immunoassay from Labsystems and the microimmunofluorescence [MIF] test) but no statistical analysis concerning possible cross-reactions between anti-C. trachomatis and anti-C. pneumoniae antibodies was presented. The analysis shows that the percentage of positive samples for immunoglobulin G (IgG) anti-C. pneumoniae antibodies, determined by either enzyme immunoassay or MIF, is always higher for positive IgG anti-C. trachomatis antibody samples than for negative ones. However, this difference was only significant when the presence of IgG anti-C. trachomatis and -C. pneumoniae antibodies was determined with the MIF test. Indeed, 92% of IgG anti-C. trachomatis antibody-positive samples also had IgG anti-C. pneumoniae antibodies while at the same time only 45% of IgG anti-C. trachomatis antibody-negative samples were found to be positive for IgG anti-C. pneumoniae antibodies (P = 0.0037, chi-square test). When the presence of IgG anti-C. trachomatis antibodies was documented by the MIF test and that of IgG anti-C. pneumoniae was identified by the Labsystems enzyme immunoassay, 77% of IgG anti-C. trachomatis antibody-positive but only 48% of the antibody-negative samples also had IgG anti-C. pneumoniae antibodies. The difference was not significant.

When the presence of IgG anti-C. trachomatis antibodies was determined with other methods, such as enzyme immunoassays using either synthetic peptides derived from species-specific epitopes in the variable domain IV of the major outer membrane protein or pgp3 as the antigen(s), the presence of IgG anti-C. pneumoniae antibodies was found in 62 to 72% of IgG anti-C. trachomatis antibody-positive samples and in 50 to 62% of antibody-negative samples. Therefore, though the differences were not significant in most cases, samples positive for anti-C. trachomatis antibody had a tendency to be more often anti-C. pneumoniae antibody-positive than do samples negative for anti-C. trachomatis antibody. However, if C. trachomatis infection was proven in these patients, the presence or absence of C. pneumoniae or C. psittaci was not demonstrated by culture, direct immunofluorescence, or nucleic acid amplification. It is therefore only possible to speculate about the presence or absence of anti-C. pneumoniae or anti-C. psittaci antibodies and about their probable cross-reactivities.

In conclusion, in our study, the detection of cross-reacting antibodies could be expected to occur more often with the MIF test than with enzyme immunoassays. Several studies have already reported that MIF specificity is lower than that generally thought (1-2–1-4, 1-6–1-9). Because MIF tests are detecting antibodies against surface protein antigens and because the protein composition of the C. pneumoniae outer membrane complex is similar to those described for C. trachomatis and C. psittaci (1-5), the detection of cross-reacting antibodies is not surprising. Moreover, recognition of the major outer membrane protein (1-4, 1-6, 1-7) and the 60-kDa proteins of the three species was shown to be cross-reactive (1-5).

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