Immunohistology of Infectious Disease


Introduction

During the last two decades, the approach to histopathologic diagnosis has been dramatically transformed by immunohistochemistry, specifically in the diagnosis and classification of tumors and, more recently, in the diagnosis of infectious diseases in tissue samples.

Pathologists play an important role in recognizing infectious agents in tissue samples from patients, providing a rapid morphologic diagnosis, and facilitating clinical decisions in patient management, particularly when fresh tissue is not available for culture. In addition, pathologists have played a central role in the identification of emerging and reemerging infectious agents and describing the pathogenic processes of emerging diseases, such as coronavirus disease 2019 (COVID-19), hantavirus pulmonary syndrome, Middle Eastern respiratory syndrome (MERS), severe acute respiratory syndrome (SARS), leptospirosis, rickettsial and ehrlichial infections, as well as the diagnosis of anthrax during the bioterrorist attacks of 2001.

Traditionally, microbial identification in infectious diseases has been made primarily through cultures and serologic assays. However, fresh tissue is not always available for culture, and culture of fastidious pathogens can be difficult and take weeks or months to yield results. Moreover, culture alone cannot distinguish colonization from tissue invasion. In addition, serologic results can be difficult to interpret in the setting of immunosuppression or when only a single sample is available for evaluation. Some microorganisms have distinctive morphologic characteristics that allow their identification histologically in formalin-fixed tissues using routine and special stains. Nevertheless, in many instances it is difficult or even impossible to identify an infectious agent specifically by conventional morphologic methods. In other instances, more than one microorganism or pathologic process may coexist.

Immunohistochemistry is one of the most powerful techniques in surgical pathology. There has been an increasing interest in the use of specific antibodies to viral, bacterial, fungal, and parasitic antigens in the detection and identification of the causative agents in many infectious diseases. The use of a specific antibody to detect a microbial antigen was first performed by Coons and associates to detect pneumococcal antigen in tissues. The advantages of immunohistochemistry over conventional staining methods ( Box 3.1 ) and the contributions of immunohistochemistry in infectious diseases ( Box 3.2 ) are substantial; in many instances, immunohistochemistry has shown high specificity, allowing the differentiation of morphologically similar microorganisms. Immunohistochemistry is especially useful when microorganisms are difficult to identify by routine or special stains, are fastidious to grow, or exhibit atypical morphology ( Box 3.3 ). It is important to understand that there may be widespread occurrence of common antigens among bacteria and pathogenic fungi, and both monoclonal and polyclonal antibodies must be tested for possible cross-reactivities with other organisms and validated before clinical use. Finally, it is important to emphasize that immunohistochemistry has several steps, and all of them can affect the result; however, in general the only limitations are the availability of specific antibodies and the preservation of epitopes. As with any other pathologic processes, establishing a final diagnosis in infectious disease pathology requires integretaion of the clinical picture, gross pathology, routine microscopic findings, and interpretation of immunohistochemical results.

BOX 3.1
Advantages of IHC in the Diagnosis of Infectious Diseases

  • 1.

    Opportunity for rapid results

  • 2.

    Reduced risk of exposure to serious infectious diseases by performance on formalin- fixed, paraffin-embedded tissue

  • 3.

    High sensitivity allowing identification of infectious agents even before morphologic changes occur

  • 4.

    Opportunities for retrospective diagnosis of individual patients and for in depth study of the disease

  • 5.

    Specific identification of infectious agents with many monoclonal antibodies and some polyclonal antibodies

BOX 3.2
Contributions of IHC to the Diagnosis of Infectious Diseases

  • 1.

    Allows identification of new human pathogens

  • 2.

    Allows microbiological-morphologic correlation establishing the pathogenic significance of microbiological results

  • 3.

    Provides a rapid morphologic diagnosis allowing early treatment of serious infectious diseases

  • 4.

    Contributes to understanding of the pathogenesis of infectious diseases

  • 5.

    Provides a diagnosis when fresh tissue is not available or when culture methods do not exist

BOX 3.3
Applications of IHC in the Diagnosis of Infectious Diseases

  • 1.

    Identification of microorganisms that are difficult to detect by routine or special stains

  • 2.

    Detection of microorganisms that are present in low numbers

  • 3.

    Detection of microorganisms that stain poorly

  • 4.

    Identification of microorganisms that are fastidious to grow or noncultivable

  • 5.

    Identification of microorganisms that exhibit atypical morphology

Table 3.1 lists some commercially available antibodies for diagnostic use in surgical pathology.

TABLE 3.1
Some Commercially Available Antibodies for Immunohistochemical Diagnosis of Infectious and Prion Diseases
Microorganism Antibody/Clone Dilution Pretreatment Source
Adenovirus Mab/20/11 and 2/6 1:2000 Proteinase K Chemicon
Bartonella. henselae Mab 1 :100 HIAR Biocare Medical
BK virus Mab/BK T.1 1 :8000 Trypsin Chemicon
Candida albicans Mab/1B12 1:400 HIAR Chemicon
Chlamydia pneumoniae Mab/RR402 1:200 HIAR Accurate
Cryptosporidium Mab/Mabc1 1:100 HIAR Novocastra
CMV Mab/DDG9/CCH2 1:50 HIAR Novocastra
Clostridium spp. Rabbit polyclonal 1:1000 None Biodesign
G. intestinalis Mab/9D5.3.1 1:50 HIAR Novocastra
Hepatitis B core antigen Rabbit polyclonal 1:2000 HIAR Dako
Hepatitis B surface antigen Mab/3E7 1:100 HIAR Dako
Herpes simplex 1 and 2 viruses Rabbit polyclonal 1:3200 HIAR Dako
Helicobacter pylori Rabbit polyclonal 1:40 Protase I Dako
HHV 8 Mab/LNA-1 1:500 HIAR Novocastra
K. pneumoniae Rabbit polyclonal 1:200 Proteinase K Biogenesis
Listeria monocytogenes Rabbit polyclonal 1:5000 Proteinase K Difco
M. pneumoniae Mab/1.B.432 1:25 HIAR US Biological
Parvovirus B19 Mab/R92F6 1:500 HIAR Novocastra
P. jirovecii Mab/3F6 1:20 HIAR Novocastra
P. falciparum
Prion
Prion
Prion
RSV
R. arrhizus
Mab/BDI400
Mab/3F4
Mab/12F10
Mab/KG9
Mab/5H5N
Mab/WSS-RA-1
1:1000
1:200
1:1000
1:1000
1:200
1:100
Proteinsae K
HIAR
Proteinase K
Proteinase K
HIAR
HIAR
Biodesign
Dako
Cayman Chemical
TSE Resource Center
Novocastra
LSBio
S. aureus
SARS-COV-2
Rabbit polyclonal
Rabbit polyclonal
1:500
1:250
Proteinase K
ER2
Biodesign
Novus Biologicals
Treponema pallidum Rabbit polyclonal HIAR Biodesign
T. gondii Rabbit polyclonal 1:320 HIAR Biogenex
West Nile virus Mab/5H10 1:400 Proteinase K Bioreliance
CMV, Cytomegalovirus; ER2, Bond Epitope Retrieval Solution 2; HIAR, heat-induced antigen retrieval; RSV, respiratory syncytial virus; TSE , transmissible spongiform encephalopathy.

Viral Infections

Immunohistochemistry has played an important role not only in the diagnosis of many viral infections, but also in the study of their pathogenesis and epidemiology. Conventionally, the diagnosis of viral infections has relied on cytopathic changes observed by routine histopathology. Several viral pathogens produce characteristic intracellular inclusions, which allow pathologists to make a presumptive diagnosis of viral infection. However, for some viral infections the characteristic cytopathic changes are subtle and sparse, requiring a meticulous search. Moreover, only 50% of the known viral diseases are associated with characteristic intracellular inclusions. In addition, formalin, which is the most commonly used fixative in histopathology, is a poor fixative for demonstrating the morphologic and tinctorial features of viral inclusions. When viral inclusions are not detected in hematoxylin-eosin stained sections, or when the viral inclusions present cannot be differentiated from those of other viral diseases, immunohistochemical techniques offer a more reliable approach to reach a specific diagnosis.

Hepatitis B

Hepatitis B virus infection constitutes an important cause of chronic hepatitis in a significant proportion of patients. In many instances, the morphologic changes induced by hepatitis B virus in hepatocytes are not typical enough to render a presumptive diagnosis of hepatitis B viral infection. In other instances, there may be so little hepatitis B surface antigen (HBsAg) that it cannot be demonstrated by techniques such as orcein staining. In these cases, immunohistochemical techniques to detect HBsAg are more sensitive than histochemical methods and are helpful in reaching diagnosis. Immunostaining for HBsAg has been used in the diagnosis of hepatitis B and in the study of carrier states. , Eighty percent or more of cases with positive serologic results for HBsAg demonstrate cytoplasmic HBsAg using immunohistochemistry. By immunoperoxidase localization, hepatitis B core antigen (HBcAg) can be demonstrated within the nuclei, the cytoplasm of hepatocytes, or both. Predominantly cytoplasmic expression of HBcAg is associated with a higher grade of hepatitis activity and diffuse immunostaining of nuclei for HBcAg generally suggests uncontrolled viral replication in the setting of immunosuppression. Immunostaining for HBsAg and HBcAg is useful in the diagnosis of recurrent hepatitis B infection in liver allografts, particularly when present with atypical histopathologic features.

Herpesviruses

Histologically, the diagnosis of herpes simplex virus (HSV) infection involves the detection of multinucleated giant cells containing characteristic molded, ground glass–appearing nuclei and Cowdry’s type A intranuclear inclusions. When there are abundant viral inclusions within infected cells, the diagnosis is usually straightforward. However, the diagnosis of HSV infection can be difficult when the characteristic intranuclear inclusions, multinucleated cells, or both are absent, or when the amount of tissue in a biopsy specimen is small. In these cases, immunohistochemistry using either polyclonal or monoclonal antibodies against HSV antigens has proven to be a sensitive and specific technique to diagnose HSV infections ( Fig. 3.1 ).

Fig. 3.1, Photomicrograph of cervical biopsy from a patient with herpes simplex virus infection showing abundant nuclear and cytoplasmic antigen. (Immunoperoxidase staining with 3-3′-diaminobenzidine [DAB] and hematoxylin countersain; ×400.)

Although polyclonal antibodies against the major HSV glycoprotein antigens are sensitive, they do not allow distinction between HSV-1 and HSV-2 because these two viruses are antigenically similar. In addition; the histologic features of HSV infection are not specific and can occur in patients with varicella-zoster virus (VZV) infection. Monoclonal antibodies against the VZV envelope glycoprotein gp1 are sufficiently sensitive and specific to allow a clear-cut distinction between HSV and VZV infections. ,

Immunohistochemistry has also been useful in demonstrating the association of human herpes virus 8 (HHV-8) with Kaposi sarcoma, primary effusion lymphoma, and multicentric Castleman disease. The diagnosis of Kaposi sarcoma may be problematic due to its broad morphologic spectrum and similar appearance to other benign and malignant neoplastic vascular lesions. Immunostaining for HHV-8 latent associated nuclear antigen-1 (LANA-1) is useful to confirm the diagnosis of Kaposi sarcoma, particularly in difficult early lesions that may mimick the appearance of interstitial granuloma annulare and when the neoplasm presents in an unusual location. In these instances, immunohistochemistry allows distinction of Kaposi sarcoma from several morphologically similar vasoproliferative lesions. Immunostaining is restricted to the nuclei of spindle cells and endothelial cells of the slit-like vascular spaces ( Fig. 3.2 ). Immunohistochemistry has also demonstrated expression of HHV-8 LANA-1 in mesothelial cells of human immunodeficiency virus (HIV)–associated recurrent pleural effusions.

Fig. 3.2, Lymph node biopsy from a patient with Kaposi sarcoma. The spindle cells show strong nuclear staining for human herpes virus 8 (HHV-8) latent associated nuclear antigen-1 (LANA-1). Endothelial cells of well-formed vascular spaces are negative. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Cytomegalovirus (CMV) continues to be an important opportunistic pathogen in immunocompromised patients; it is estimated that 30% of transplant recipients experience CMV disease. The range of organ involvement in post-transplant CMV disease is wide; hepatitis occurs in 40% of liver transplant recipients, and pneumonitis is more frequently seen in heart and heart-lung transplant patients.

Histologic diagnosis of CMV in fixed tissues usually rests on the identification of characteristic cytopathic effects, including intranuclear or cytoplasmic inclusions, or both. However, histologic examination lacks sensitivity, and in some cases atypical cytopathic features can be confused with reactive or degenerative changes. Additionally, up to 38% of patients with gastrointestinal CMV disease fail to demonstrate any inclusions. In these cases, immunohistochemistry using monoclonal antibodies against early and late CMV antigens allows the detection of CMV antigens in the nucleus and cytoplasm of infected cells ( Fig. 3.3 ). The sensitivity of immunohistochemistry for detecting CMV infection ranges from 78% to 93%. , In addition, immunohistochemistry may allow detection of CMV antigens early in the course of the disease when cytopathic changes have not yet developed ; for example, CMV early nuclear antigen is expressed 9 to 96 hours after cellular infection and indicates early active viral replication. Immunohistochemistry has played a key role in the detection of CMV infection in patients with steroid refractory ulcerative colitis, leading to recommendations for the routine use of immunohistochemistry for the detection of CMV in the evaluation of these patients. , CMV immunostaining has been used in detecting occult CMV infection of the central nervous system of liver transplant patients who develop neurologic complications. It has also been used to demonstrate a high frequency of CMV antigens in tissues from first trimester abortions. CMV is the most common opportunistic organism found in liver biopsies from transplant patients, but the incidence of CMV hepatitis appears to be decreasing due to better prophylactic treatments. Although CMV hepatitis presents with characteristic neutrophilic aggregates within the liver parenchyma, atypical features suggestive of acute rejection or changes indistinguishable from those of any other viral hepatitis are occasionally observed. In addition, parenchymal neutrophilic microabscesses have been described in cases with no evidence of CMV infection. It is in these cases where immunostaining for CMV antigens is most useful in diagnosing CMV.

Fig. 3.3, Colon biopsy of a patient with steroid-refractory ulcerative colitis. Rare epithelial cells show intranuclear cytomegalovirus (CMV) antigen. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

The sensitivity of immunohistochemistry is better than light microscopic identification of viral inclusions and compares favorably with culture and in situ hybridization. , , , , Immunohistochemical assays can be completed faster than the shell vial culture technique, allowing for rapid results that are important for early anti-CMV therapy.

Other herpesvirus infections that have been diagnosed using immunohistochemical methods include human herpesvirus 6 infection and Epstein-Barr viral infection. Immunohistochemistry has been used to identify Epstein-Barr virus (EBV) latent membrane protein-1 in cases of Hodgkin lymphoma and post-transplant lymphoproliferative disorder ( Fig. 3.4 ).

Fig. 3.4, Epstein-Barr virus LMP-1 within cytoplasm of characteristic Reed-Sternberg cells in a case of Hodgkin’s lymphoma. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Adenoviruses

Adenovirus is increasingly recognized as a cause of morbidity and mortality among immunocompromised patients owing to transplant and congenital immunodeficiency. , Rarely has adenovirus infection been described in HIV-infected patients. Characteristic adenovirus inclusions are amphophilic, intranuclear, homogeneous, and glassy, however, in some cases the infection may contain only rare cells showing the characteristic cytopathic effect. In addition, other viral inclusions, including CMV, human papilloma virus, HSV, and VZV, can be mistaken for adenovirus inclusions and vice versa. In these circumstances, immunohistochemical assay may be necessary for a definitive diagnosis. A monoclonal antibody that is reactive with 41 serotypes of adenovirus has been used in an immunohistochemical technique to demonstrate intranuclear adenoviral antigen in immunocompromised patients ( Fig. 3.5 ). However, many other antibodies react with only a limited number of adenovirus serotypes. Histologic diagnosis of adenovirus colitis is difficult and is usually underdiagnosed. Moreover, in immunosuppressed patients the incidence of coinfection with other viruses is high, and the presence of adenovirus tends to be overlooked. Immunohistochemical staining has been of value in differentiating adenovirus colitis from CMV colitis. ,

Fig. 3.5, Adenovirus pneumonia in a heart transplant patient who developed acute respiratory distress syndrome (ARDS) and respiratory failure. Infected cells within necrotizing exudate show intranuclear reactivity with antibody to adenovirus antigen. Some cells show inclusions with a clear halo around them, making a differential diagnosis from cytomegalovirus (CMV) difficult on hematoxylin and eosin stain. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Parvovirus B19 Infection

Parvovirus B19 has been associated with asymptomatic infections, erythema infectiosum, acute arthropathy, aplastic crisis, hydrops fetalis, chronic anemia, and red cell aplasia. In addition, Parvovirus B19 infection has been recognized as an important cause of severe anemia in immunocompromised leukemic patients receiving chemotherapy. The diagnosis of parvovirus infection can be achieved by identifying typical findings in bone marrow specimens, including decreased or absent red cell precursors, giant pronormoblasts, and eosinophilic or amphophilic intranuclear inclusions in erythroid cells. , Because intravenous immunoglobulin therapy is highly effective, a rapid and accurate diagnostic method is important. Immunohistochemistry with a monoclonal antibody against VP1 and VP2 capsid proteins has been used as a rapid and sensitive method to establish the diagnosis of parvovirus B19 infection in formalin-fixed, paraffin-embedded tissues. Immunohistochemistry is of particular help in detecting parvovirus B19 antigen in cases with sparse inclusions, to study cases not initially identified by examination of routinely stained tissue sections, or in cases of hydrops fetalis where there is advanced cytolysis ( Fig. 3.6 ). , , Several studies have found a good correlation between morphologic, immunohistochemical, in situ hybridization, and polymerase chain reaction (PCR) results. , , ,

Fig. 3.6, Hydrops fetalis caused by parvovirus B19 infection. Normoblasts within the villous capillaries show intranuclear viral antigen. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Viral Hemorrhagic Fevers

Since the 1970s, numerous emerging and reemerging agents of viral hemorrhagic fevers have attracted the attention of pathologists. Pathologists have played an important role in the identification of these agents and in supporting epidemiologic, clinical, and pathogenetic studies of the emerging viral hemorrhagic fevers. , , Viral hemorrhagic fevers are often fatal, and in the absence of bleeding or organ manifestations these diseases are clinically difficult to diagnose and frequently require handling and testing of potentially dangerous biological specimens. In addition, histopathologic features are not pathognomonic, and they can resemble other viral, rickettsial, and bacterial (e.g., leptospirosis) infections. Immunohistochemistry is essential and has been successfully and safely applied to the diagnosis and study of the pathogenesis of these diseases.

Several studies have established the utility of immunohistochemistry as a sensitive, safe, and rapid diagnostic method for viral hemorrhagic fevers such as yellow fever ( Fig. 3.7 ), dengue hemorrhagic fever, , Crimean-Congo hemorrhagic fever, Argentine hemorrhagic fever, Venezuelan hemorrhagic fever, and Marburg disease. Additionally, a sensitive, specific, and safe immunostaining method has been developed to diagnose Ebola hemorrhagic fever in formalin-fixed skin biopsies ( Fig. 3.8 ). Immunohistochemistry demonstrated that Lassa virus, the causative agent of Lassa fever, primarily targets endothelial cells, mononuclear inflammatory cells, and hepatocytes ( Fig. 3.9 ).

Fig. 3.7, Yellow fever. Abundant yellow fever viral antigens are seen within hepatocytes and Kupffer cells. (Immunoperoxidase staining with 3-amino-9-ethylcarbazole [AEC] and hematoxylin counterstain; ×400.)

Fig. 3.8, Extensive Ebola viral antigens are seen primarily within fibroblasts in the dermis of a skin specimen from a fatal case of Ebola hemorrhagic fever. (Immunoalkaline phosphatase with napthol fast red substrate and hematoxylin counterstain, original magnification ×20.)

Fig. 3.9, Lassa fever. Liver from a patient with Lassa fever, scattered hepatocytes and reticuloendothelial cells show reactivity with monoclonal antibody to Lassa virus. (Naphthol fast red substrate and hematoxylin counterstain, original magnification ×100.)

Polyomaviruses

BK virus infections are frequent during infancy. In immunocompetent individuals, the virus remains latent in the kidneys, central nervous system, and B lymphocytes. In immunocompromised patients, the infection reactivates and spreads to other organs. BK virus nephropathy is an important cause of graft failure in patients with renal transplant, with prevalence varying from 2% to 4.5% in different transplant centers. , Since specific clinical signs and symptoms are lacking in BK virus nephropathy, the diagnosis can only be made histologically in a graft biopsy. In the kidney, the infection is associated with mononuclear interstitial inflammatory infiltrates and tubular atrophy, findings that can be difficult to distinguish from acute rejection. Further, the cytopathic changes observed in BK virus infection are not pathognomonic and can be observed in other viral infections. Moreover, in early BK virus infection, there are minimal or no histologic changes, although immunohistochemistry can identify viral antigens. , In this setting, immunohistochemistry with an antibody against the large T antigen of SV40 virus has been effective in demonstrating BK virus infection ( Fig. 3.10 ). , ,

Fig. 3.10, Immunohistochemical detection of SV40-T antigen in the nuclei of tubular cells in a renal transplant patient with BK virus-associated nephropathy. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

The human polyomavirus JC is a double-stranded DNA virus that causes progressive multifocal leukoencephalopathy (PML). This fatal demyelinating disease is characterized by cytopathic changes in oligodendrocytes and bizarre giant astrocytes. In addition to detection by antibodies to SV40-T antigen, immunohistochemistry using a polyclonal rabbit antiserum against the protein VP1 is a specific, sensitive, and rapid method for confirming the diagnosis of PML. JC virus antigen is usually seen within oligodendrocytes ( Fig. 3.11 ) and occasional astrocytes, and antigen-bearing cells are more commonly seen in early lesions.

Fig. 3.11, Progressive multifocal leukoencephalopathy: SV40-T antigen in the nuclei of enlarged oligodendrocytes in a patient with JC virus infection. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Other Viral Infections

Immunohistochemistry has also been used to confirm the diagnosis of respiratory viral diseases such as influenza A, H1N1 (swine flu), H5N1 (avian flu), and respiratory syncytial virus infections ( Fig. 3.12 ) when cultures were not available.

Fig. 3.12, Immunostaining of respiratory syncytial virus (RSV) antigens in desquamated bronchial and alveolar lining cells using a monoclonal antibody. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

The diagnosis of rabies relies heavily on histopathologic examination of tissues to demonstrate the characteristic cytoplasmic inclusions (Negri bodies). In a large number of cases, Negri bodies may be inconspicuous and so few that confirming the diagnosis of rabies may be extremely difficult. Furthermore, in non-endemic areas the diagnosis of rabies is usually not suspected clinically. Also, patients may present with ascending paralysis, rather than one of the more common presenting signs. In these settings, immunohistochemical staining is a very sensitive, safe, and specific diagnostic tool for rabies ( Fig. 3.13 ). Other viral agents that can be diagnosed using immunohistochemical methods include enteroviruses, eastern equine encephalitis virus, and rotavirus.

Fig. 3.13, Immunostaining of rabies viral antigens in neurons of the CNS using a rabbit polyclonal antibody. Red precipitate corresponds to Negri inclusions by hematoxylin and eosin staining. (Immunoalkaline phosphatase with naphthol fast red substrate and hematoxylin counterstain, original magnification ×40.)

Immunohistochemical staining has been used in the histopathologic diagnosis of viral hepatitis C; however, immunohistochemistry for this virus is not superior to serologic assays and detection of hepatitis C virus (HCV) RNA in serum.

Bacterial Infections

Among bacterial infections, the greatest number of immunohistochemical studies have been performed in the investigation of Helicobacter pylori . A few studies have evaluated the use of immunohistochemistry in other bacterial, mycobacterial, rickettsial, and spirochetal infections.

Antigen retrieval is generally not required for the immunohistochemical demonstration of bacteria in fixed tissue. However, interpretation of the results can be complicated by the fact that many of these antibodies will cross-react with other bacteria. Moreover, antibodies may react with only portions of the bacteria, and they may label remnants of bacteria or spirochetes when viable organisms are no longer present.

Helicobacter pylori Infection

Gastric infection by H. pylori results in chronic active gastritis and is strongly associated with lymphoid hyperplasia, gastric lymphomas, and gastric adenocarcinoma. Heavy infections with numerous organisms are easily detected on routine hematoxylin and eosin–stained tissues; however, the detection rate is only 66% with many false-positive and false-negative results. , Conventional histochemical methods such as silver stains are more sensitive than hematoxylin and eosin in detecting H. pylori . However, for the detection of scant numbers of organisms, immunohistochemistry has proved to be highly specific and sensitive, less expensive when all factors are considered, superior to conventional histochemical methods, and has low interobserver variation ( Fig. 3.14 ). , Treatment for chronic active gastritis and H. pylori infection can change the shape of the microorganism, making difficult its identification and differentiation from extracellular debris or mucin globules. In these cases, immunohistochemistry improves the rate of successful identification of the bacteria even when histologic examination and cultures are falsely negative. Experts currently recommend using IHC for identification of H. pylori when there is chronic active gastritis and H&E does not detect H. pylori organisms. In patients with chronic inactive gastritis and no H. pylori organisms visible on H&E, IHC use is recommended when there is gastroduodenal ulceration, underlying gastric MALT lymphoma or adenocarcinoma, duodenal lymphocytosis, or presence of well-formed lymphoid follicles with germinal centers in the stomach. Similarly, IHC is also recommended for patients previously treated for H. pylori infection in the presence of chronic inactive gastritis with no visible H. pylori organisms on H&E. Helicobacter heilmannii belongs to the Helicobacter family and is a less common causative agent of chronic gastritis found in a few gastric biopsies. This bacterium has been associated with mild chronic gastritis, peptic ulceration, and rarely gastric adenocarcinoma and MALT-lymphoma. Commercially available polyclonal antibodies against H. pylori cross-react with H. heilmannii antigens, allowing for detection of this microorganism in gastric biopsies with a paucity of bacteria ( Fig. 3.15 ). Recently, polyclonal antibodies against Treponema pallidum have been described to immunostain gastric biopsies with H. heilmannii gastritis.

Fig. 3.14, Numerous curved Helicobacter pylori in the superficial gastric mucus are clearly demonstrated by immunoperoxidase staining in this patient with chronic active gastritis. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

Fig. 3.15, Helicobacter heilmannii chronic gastritis. Immunostaining with polyclonal anti- Helicobacter pylori antibody demonstrates long spiral bacteria in gastric pits. (Immunoperoxidase staining with diaminobenzidine [DAB] and hematoxylin counterstain; ×400.)

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here