Assessment of Chlamydia trachomatis-specific IgA and IgG serum antibodies in genitourinary Chlamydia trachomatis infection--comparative study between HITAZYME and IPAzyme.

We assessed the C. trachomatis antibody assay kit HITAZYME (Hitachi Chemical Co., Ltd.) using clinical specimens. This kit is based on an enzyme immunoassay (EIA) which utilized purified Chlamydia trachomatis outer membrane antigen as the solid phase antigen. Twenty-nine untreated male urethritis patients, 816 pregnant housewives, 188 cervicitis patients, and 76 pelvic inflammatory disease patients were tested. Agreement between the HITAZYME test and antigen detection in infected area was assessed, and a comparison was made with IPAzyme (a commercially available indirect immunoperoxidase assay kit). 1) Summary of HITAZYME and IPAzyme IgA: Agreement between the two assays was relatively good, i.e., 82.6% (916/1109). However, 5.5% (61/1109) were HITAZYME (-), IPAzyme (+), and 11.9% (132/1109) were HITAZYME (+), IPAzyme (-). Thus, in quite a few cases the results did not agree. IgG: Agreement between the two assays was 73.7% (817/1109). Agreement was relatively low, 24.4% (271/1109) were HITAZYME (-), IPAzyme (+). 2) In the cases of disagreement, more specific Western blot analysis was performed to check the reactivity of the anti-C. trachomatis antibody. When IgA was used, agreement between HITAZYME and Western blot analysis was 69.6% (16/23), and agreement between IPAzyme and Western blot analysis was 30.4% (7/23), whereas when IgG was used, agreement between HITAZYME and Western blot analysis was 80.0% (12/15), and agreement between IPAzyme and Western blot analysis was 20.0% (3/15). There was significantly greater agreement with HITAZYME than with IPAzyme. In other words, HITAZYME had greater specificity when reacted with C. trachomatis antigen than IPAzyme. 3) The IgA antibody-positive rate in antigen (+) cases (male urethritis: 72.7%, pregnant housewives: 65.7%, cervicitis: 70.3%, pelvic inflammatory disease: 70.0%) was significantly (p < 0.01) higher than in antigen (-) cases (male urethritis: 16.7%, pregnant housewives: 13.6%, cervicitis: 22.6%, pelvic inflammatory disease: 30.4%). Therefore, IgA antibody can serve as a suitable indicator for active infection. 4) The IgG antibody-positive rate in antigen (-) female cases was 15.5% using HITAZYME and significantly (p < 0.01) lower than with IPAzyme. HITAZYME had greater specificity than IPAzyme. In conclusion, HITAZYME has relatively good sensitivity and specificity. Moreover, since it is an EIA assay, it allows objective evaluation of results. It permits processing of a large number of specimens because it is easy to perform. Thus, HITAZYME is a superior antibody assay for C. trachomatis. It can be used when antigen tests are difficult to perform. It is strongly anticipated that HITAZYME will be able to be used clinically as a screening test.