6. Concluding remarks

Undoubtedly, the detection of causative pathogens in the inflammatory lesion is the key step directing to the correct histopathological diagnosis of infectious diseases. Even if the specificity of the serum is unknown, the final diagnosis can be reached, based on the morphology and distribution of the positive signals, when combined with tissue reactions, laboratory data and clinical features. In the present article, the author introduced two different approaches using low-specificity antisera. The targets were formalin-fixed and paraffin-embedded sections. One approach is the use of commercially available rabbit antisera showing wide crossreactivity to a variety of bacteria, and another is the use of diluted patients'sera.

Immunostaining using plural antimicrobial antisera commonly yielded clear positivity with low background, because of poor cross-reactivity of bacterial antigens to human cells and tissues. The approach described here was aimed at visualizing the causative bacteria within infectious lesions in routinely prepared paraffin sections through a wide cross-reactivity shown by low-specificity rabbit antisera against four kinds of bacteria.

Immunostaining using patients'sera is also quite useful in making the histopathological diagnosis. Occasionally, IgG in the patients'sera showed crossreactivity to related pathogens wider than expected. In bacterial and fungal infection, the sera served as pan-bacterial and pan-fungal probes, respectively. Despite such broad/low specificity, this convenient procedure is excellent in selectively identifying the pathogen within the lesion in question. In viral, protozoal, and

Low-Specificity and High-Sensitivity Immunostaining for Demonstrating Pathogens… DOI: http://dx.doi.org/10.5772/intechopen.85055

helminthic infection, the specificity was much narrower with limited crossreactivities, and once the specificity is known, the patients'sera turn to become specific primary antibodies for identifying pathogens in the following new cases.

In the latter approach, what one should do is, instead of ordering an expensive antibody of unknown quality, to make a brief phone call to clinicians or laboratory technicians to ask to save a small aliquot of patients'sera, soon after microscopic confirmation of the host response in histopathology specimens. This is particularly true when specific antibodies are not listed in the commercial catalog. Of note is that informed consent is unnecessary when the patient's serum is utilized primarily for making a diagnosis of the patient's own. When the serum is applied to immunostaining for another case as the primary antibody, the author strongly recommends linking the preserved serum non-anonymously.

The author sincerely hopes that the approaches shown here will be applied to the histopathological diagnosis of infectious diseases in the readers' laboratories.
