Definitive diagnosis of lymphogranuloma venereum is impeded by difficulty in culturing the causative agent and by serologic cross-reactivity between Chlamydia trachomatis L1, L2, and L3, which can cause the disease, and the many other serotypes of C. trachomatis, which do not. In a 23-year-old man with massive rectal bleeding, an exudative rectal ulcer, and inguinal lymphadenopathy, serologic findings were compatible with a recent lymphogranuloma venereum infection, but stains and cultures of lymph-node aspirates were negative, and biopsy specimens of the rectum and lymph nodes showed only nonspecific inflammatory changes. A diagnosis of lymphogranuloma venereum was made when intracellular organisms and inclusion bodies were demonstrated in rectal submucosal tissue by fluorescein-tagged monoclonal antibodies directed against both chlamydial group antigens and L2 serotype antigen. This technique was of particular value in this patient because it specifically identified an unusual cause of severe gastrointestinal bleeding.
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