4. Immunohistochemical demonstration of bacterial antigens using four kinds of antibacterial antisera with a wide cross-reactivity to a variety of bacteria

We diagnostic pathologists encounter lesions strongly suggestive of infection but with poor clinical information or with difficulty in microscopically supposing a causative pathogen. In such situations, immunostaining employing the abovementioned four kinds of rabbit antisera is worthy of application [8, 19]. We can prove the existence of pathogens in a certain part of the lesion. Background staining is negligible, whereas B. cereus antiserum may be cross-reactive to the nuclei of human cells in some cases (see Figure 16). In this type of application, we must abandon the specificity of immunostaining, and instead we welcome to accept the sensitivity of detection.

Regrettably enough, the availability of antisera against microbes from commercial sources has become limited. In fact, antisera against BCG and E. coli are no longer available from Dako (Agilent) company [16]. The author is afraid that this may hamper the standardization of immunohistochemical diagnosis of infectious diseases.

Table 3 summarizes reactivities of various microbes to the four kinds of rabbit antibacterial antisera.

#### 4.1 E. coli antigens in leptospirosis

Hamster liver experimentally infected with Leptospira interrogans is shown in Figure 10. Not only Leptospira antiserum (the gift from Prof. Shinichi Yoshida, Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Fukuoka) but also E. coli antiserum were reactive to spiral-shaped bacteria in the hepatic sinusoid [19]. Pathogens phagocytized by activated Kupffer cells were visualized only by Leptospira antiserum [32]. E. coli antiserum was not crossreactive with T. pallidum in the syphilitic lesion, while T. pallidum antiserum was unreactive with Leptospira in the hamster liver.

Figure 8.

Immunohistochemistry - The Ageless Biotechnology

antigens.

Figure 9.

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E. coli immunostaining I (upper panels, rectal erosion; lower panels, rectal malacoplakia; left, H&E; right, immunostaining using E. coli antiserum). E. coli-related antigens are detectable in eroded surface of rectal mucosa and in malacoplakia of the rectum. Michaelis-Gutmann bodies (arrows) in the cytoplasm of macrophages, the microscopic hallmark of malacoplakia, are round, basophilic, and immunoreactive to E. coli

E. coli immunostaining II (upper panels, opportunistic E. coli-induced pneumonia; lower panels, E. coliinduced emphysematous pyelonephritis in a diabetic patient; left, H&E; right, immunostaining using E. coli antiserum). Positive rod-shaped signals are clearly seen in the cytoplasm of phagocytes in nosocomial bronchopneumonia and in severely affected kidney with numerous colonies of gas-forming bacteria.
