Aids to pathologic diagnosis In most of the pathologic material, the pathologist is usually able to make a direct diagnosis. However, in about 10% of cases, the diagnosis is somewhat difficult for various reasons. For this reason, in addition to the fact that more sections should be made and carefully observed, the application of new techniques is indispensable. These new techniques include: electron microscopy, histochemistry, immunohistochemistry, PCR, FISH, etc. Among them, the most applied technique is immunohistochemistry. The emergence and development of immunohistochemical staining techniques (immunohistochemical techniques for short) has brought a revolutionary change to traditional pathology. Most of the substances with antigenic properties in tissues or cells can be displayed in situ by immunohistochemical techniques as long as the corresponding antibodies are available, making the purely morphological pathology develop into a modern pathology combining morphological and immune signals. Immunohistochemical techniques have been used for clinical pathology diagnosis for more than a decade, and in continuous practice, they can + detect a variety of items such as diagnosis, differential diagnosis, and drug resistance genes for diseases. The following is a brief description of the current status of diagnosis and research of several types of diseases by commonly used immunohistochemistry techniques. 1, infectious diseases: Currently mostly used to detect viruses, bacteria, protozoa, pneumocystis, fungi, mycoplasma, chlamydia and other pathogenic microorganisms. 2, immunological diseases or diseases related to immunological development mechanism: such as glomerulonephritis and transplant rejection reaction and other lesions in the tissue detection and characterization of various immunoglobulins, complement, etc. 3.Tumor (1)Differential diagnosis of histological type of tumor. For hypodifferentiated or undifferentiated malignant tumors, it is often difficult to determine the histological type or even the basic tissue origin due to the lack of differentiation characteristics of tumor cells. If we use non-specific antibodies, it is possible to initially distinguish the histological type, on the basis of which specific antibodies can be selected for further identification. (2) Diagnosis of the origin of metastases. Immunohistochemical techniques are useful to determine the histological origin of malignant tumors in metastases where no primary tumor is clinically detected. (3) Diagnosis and histologic typing of malignant lymphomas and leukemias. Cells of the lymphoid and myeloid systems differ in the antigens expressed by cells at different stages of differentiation and maturation and in the activation of peripheral lymphocytes, so various malignant lymphomas and leukemias require immunohistochemical techniques to detect the antigens expressed by tumor cells to differentiate the types. (4) Detection of hormones and related proteins expressed by tumor cells is used to diagnose and classify endocrine and neuroendocrine tumors, or to determine the abnormal secretory function of non-endocrine system tumors. (5) To suggest the benignity or malignancy of proliferating cells or to estimate the biological behavior of tumors. For example, the monoclonal or polyclonal nature of B-lymphocyte proliferation is detected with light chain antibodies to immunoglobulins to distinguish whether it is tumorigenic or reactive proliferation, etc. The detection of some malignancy-related indicators, such as P53, Ki-67, PCNA, VEGF, TOPII, etc., can help to determine the prognosis of tumors. (6) The choice of drugs for malignancy. For example, detection of ER, PR, C-erbB-2 in breast cancer and CD117 in gastrointestinal mesenchymal tumor. Rational selection of the use of immunohistochemical techniques, continuous improvement of the level of pathological diagnosis and better service to patients are the goals of our pathology department as always.