 subsequent to the first report in the 1940s on incubation of tissue sections with fluorescein - conjugated antibodies for localization of antigens , a great number of modifications were introduced to improve the validity of immunohistochemistry which has become a growingly popular tool . 
 the use of immunoenzymatic techniques eliminates the need for expensive fluorescence microscopy equipment , the lack of permanency of preparations and the lack of electron density required in ultrastructural localization of antigens . 
 regardless of the technique , it is also important to choose a correct fixation which allows the proper preservation of antigens and morphology and the penetration of antibodies through the entire thickness of the preparation . a variety of immunohistochemical techniques 
 have been applied to study several components of the lung , such as collagen , surface active material , lung specific antigens , and enzymes and the detection of tumor markers , immunoglobulins and infectious agents in the respiratory system which is reviewed . the large surface area and the multiplicity of cell types provided by the respiratory tract epithelium of humans for exposure to microbial as well as toxic substances in the environment make this organ system very vulnerable but a good early indicator of adverse health effects . 
 immunohistochemistry provides valuable information complementary to the immunochemical and biochemical characterization of this barrier.imagesfigure 2.figure 3.figure 3.figure 4.figure 4.figure 5 . 
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