Differential expression of HLA-DR, HLA-DP, HLA-DQ and associated invariant chain (Ii) in normal colorectal mucosa, adenoma and carcinoma

Aberrant Expression of and Cell Death Induction by Engagement of the MHC-II Chaperone CD74 in Anaplastic Large Cell Lymphoma (ALCL)

Simple Summary

Anaplastic large cell lymphoma (ALCL) is a lymphoid malignancy considered to be derived from T cells. Currently, two types of systemic ALCL are distinguished: anaplastic lymphoma kinase (ALK)-positive and ALK-negative ALCL. Although ALK⁺ and ALK⁻ ALCL differ at the genomic and molecular levels, various key biological and molecular features are highly similar between both entities. We have developed the concept that both ALCL entities share a common principle of pathogenesis. In support of this concept, we here describe a common deregulation of CD74, which is usually not expressed in T cells, in ALCL. Ligation of CD74 induces cell death of ALCL cells in various conditions, and an anti-CD74-directed antibody-drug conjugate efficiently kills ALCL cell lines. Furthermore, we reveal expression of the proto-oncogene and known CD74 interaction partner MET in a fraction of ALCL cases. These data give insights into ALCL pathogenesis and might help to develop new treatment strategies for ALCL.

Abstract

In 50–60% of cases, systemic anaplastic large cell lymphoma (ALCL) is characterized by the t(2;5)(p23;q35) or one of its variants, considered to be causative for anaplastic lymphoma kinase (ALK)-positive (ALK⁺) ALCL. Key pathogenic events in ALK-negative (ALK⁻) ALCL are less well defined. We have previously shown that deregulation of oncogenic genes surrounding the chromosomal breakpoints on 2p and 5q is a unifying feature of both ALK⁺ and ALK⁻ ALCL and predisposes for occurrence of t(2;5). Here, we report that the invariant chain of the MHC-II complex CD74 or li, which is encoded on 5q32, can act as signaling molecule, and whose expression in lymphoid cells is usually restricted to B cells, is aberrantly expressed in T cell-derived ALCL. Accordingly, ALCL shows an altered DNA methylation pattern of the CD74 locus compared to benign T cells. Functionally, CD74 ligation induces cell death of ALCL cells. Furthermore, CD74 engagement enhances the cytotoxic effects of conventional chemotherapeutics in ALCL cell lines, as well as the action of the ALK-inhibitor crizotinib in ALK⁺ ALCL or of CD95 death-receptor signaling in ALK⁻ ALCL. Additionally, a subset of ALCL cases expresses the proto-oncogene MET, which can form signaling complexes together with CD74. Finally, we demonstrate that the CD74-targeting antibody-drug conjugate STRO-001 efficiently and specifically kills CD74-positive ALCL cell lines in vitro. Taken together, these findings enabled us to demonstrate aberrant CD74-expression in ALCL cells, which might serve as tool for the development of new treatment strategies for this lymphoma entity.

Targeting the MHC Class II antigen presentation pathway in cancer immunotherapy

The success of immunotherapy relies on the participation of all arms of the immune system and the role of CD4+ T lymphocytes in preventing tumor growth is now well established. Understanding how tumors evade immune responses holds the key to the development of cancer immunotherapies. In this review, we discuss how MHC Class II expression varies in cancer cells and how this influences antitumor immune responses. We also discuss the means that are currently available for harnessing the MHC Class II antigen presentation pathway for the development of efficient vaccines to activate the immune system against cancer.

The Major Histocompatibility Complex Class II-CD4 Immunologic Synapse in Alcoholic Hepatitis and Autoimmune Liver Pathology: The Role of Aberrant Major Histocompatibility Complex Class II in Hepatocytes

The major histocompatibility complex class II (MHC II)-CD4 immunologic synapse is classically described between the T-cell receptor of CD4-positive lymphocytes and MHC II on antigen-presenting cells. This interaction and others between surrounding costimulatory and checkpoint molecules promote differentiation of naïve CD4 T lymphocytes into helper T cells subtypes, including types 1, 2, and 17 helper T cells, that have more tailored immunologic responses. Although MHC II is mainly produced by professional antigen-presenting cells, it can be aberrantly produced by other cell types, including hepatocytes in various liver pathologies, such as autoimmune hepatitis and alcoholic hepatitis. This can lead to direct targeting of hepatocytes by CD4-positive lymphocytes, which form an immunologic synapse with the hepatocyte. The lymphocytes internalize the MHC II-CD4 complexes in a phagocytosis-like mechanism and in the process eat the hepatocyte piece by piece. We review the evidence for this mechanism and the role of these autoimmune responses in various liver diseases, including alcoholic hepatitis, autoimmune hepatitis, and primary biliary cirrhosis. The role of aberrant MHC II in malignancy, including hepatocellular carcinoma, is also reviewed. Further understanding of this mechanism can lead to better understanding of the immune mechanisms involved in these liver pathologies, with potential diagnostic and therapeutic applications.

HLA Class-II Expression in Human Tumors

HLA class II molecules play a pivotal role in antigen presentation to T lymphocytes. This chapter analyzed the expression of these molecules in different human tumors and their role in cancer progression. The possible connection between tumor HLA class II expression and the pathogenesis of autoimmune diseases is discussed.

PNA: A Marker of Neoplastic Progression and Differentiation in the Gastrointestinal Tract

We examined 35 cases of stomach carcinoma and 40 cases of colonic carcinoma with PNA associated with peroxidase (peanut agglutinin, lectin which binds to the terminal disaccharide galactose β (1, 3)-N-acetil-galacto-samine).

In this way evaluation of the functional aspects of the normal-neoplastic sequence was undertaken. This method was carried out for histological and ultrastructural investigations. The results obtained in both cases showed a different reactivity in the evolution of neoplastic disease: in fact, positivity in dysplasia is finely granular intracytoplasmic, whereas in well-differentiated neoplastic transformation such a reactivity is preferentially localized along the cellular membranes, with restoration of gross positivity in the cytoplasm for the poorly-differentiated neoplasm. We therefore believe PNA to be a marker not only of neoplastic progression but of differentiation as well: we also hypothesize it to reveal glycoprotein groups with possible antigenic power, involved in immunologic interactions between tumor and host.

HLA class II antigen-processing pathway in tumors: Molecular defects and clinical relevance

The human leukocyte antigen (HLA) class II antigen-processing machinery (APM) presents to cognate CD4⁺ T-cells antigenic peptides mainly generated from exogeneous proteins in the endocytic compartment. These CD4⁺ T cells exert helper function, but may also act as effector cells, thereby recognizing HLA class II antigen-expressing tumor cells. Thus, HLA class II antigen expression by tumor cells influences the tumor antigen (TA)-specific immune responses and, depending on the cancer type, the clinical course of the disease. Many types of human cancers express HLA class II antigens, although with marked differences in their frequency. Some types of cancer lack HLA class II antigen expression, which could be due to structural defects or deregulation affecting different components of the complex HLA class II APM and/or from lack of cytokine(s) in the tumor microenvironment. In this review, we have summarized the information about HLA class II antigen distribution in normal tissues, the structural organization of the HLA class II APM, their expression and regulation in malignant cells, the defects, which have been identified in malignant cells, and their functional and clinical relevance.

Antigen processing and immune regulation in the response to tumours

The MHC class I and II antigen processing and presentation pathways display peptides to circulating CD8⁺ cytotoxic and CD4⁺ helper T cells respectively to enable pathogens and transformed cells to be identified. Once detected, T cells become activated and either directly kill the infected / transformed cells (CD8⁺ cytotoxic T lymphocytes) or orchestrate the activation of the adaptive immune response (CD4⁺ T cells). The immune surveillance of transformed/tumour cells drives alteration of the antigen processing and presentation pathways to evade detection and hence the immune response. Evasion of the immune response is a significant event tumour development and considered one of the hallmarks of cancer. To avoid immune recognition, tumours employ a multitude of strategies with most resulting in a down-regulation of the MHC class I expression at the cell surface, significantly impairing the ability of CD8⁺ cytotoxic T lymphocytes to recognize the tumour. Alteration of the expression of key players in antigen processing not only affects MHC class I expression but also significantly alters the repertoire of peptides being presented. These modified peptide repertoires may serve to further reduce the presentation of tumour-specific/associated antigenic epitopes to aid immune evasion and tumour progression. Here we review the modifications to the antigen processing and presentation pathway in tumours and how it affects the anti-tumour immune response, considering the role of tumour-infiltrating cell populations and highlighting possible future therapeutic targets.

Prediction of Outcome in Diffuse Large Cell Lymphoma by the Major Histocompatibility Complex Class II (HLA-DR, DP, DQ) and Class I (HLA-A, B, C) Phenotype

Ninety-nine consecutive diffuse large cell lymphoma (DLCL) patients were studied by immunohistochemistry to determine whether clinical outcome was predicted by major histocompatibility complex (MHC) antigen phenotypic expression. Statistically significantly shorter disease free survival (p = 0.005), but not overall survival (p = 0.47), was observed when patient lymphomas failed to express class I MHC antigens. We also observed significantly reduced survival of class II MHC HLA-DP negative patients (p = 0.038). This extends our previous finding of poor outcome with absent class II MHC HLA-DR in DLCL(1) to other MHC antigens and demonstrates that the phenomenon of defective class II antigen expression comprises 16% of these DLCL patients. Known clinical parameters predictive of prognosis were equally distributed between phenotypic groups. These findings indicate that aberrancy of immune phenotype in DLCL is critical to patient outcome and we speculate that loss of MHC expression may confound host immunosurveillance and tumor containment.

Revisiting the structural basis and energetic landscape of susceptibility difference between HLA isotypes to allergic rhinitis

The human leukocyte antigen class II (HLA II) molecules are implicated in the immunopathogenesis of allergic rhinitis (AR). The HLA II contains three allelic isotypes HLA-DR, -DQ, and -QP that exhibit considerably different susceptibility to AR. Here, we investigated the structural basis and energetic landscape of the susceptibility difference between the three HLA II isotypes to AR by combining computational analysis and experimental assay. Multiple sequence alignment revealed a low conservation among the three subtypes with sequence identity of ∼10% between them, suggesting that the peptide repertoires presented by HLA-DR, -DP and -DQ are not overlapped to each other, and they may be involved in different immune functions and dysfunctions. Structural analysis imparted that the antigenic peptides are rooted on the peptide-binding groove of HLA molecules and hold in a PPII-like helical conformation. Subsequently, the interaction behavior of 17 AR allergen-derived peptides with HLA-DR, -DP and -DQ was investigated using a statistics-based quantitative structure-activity relationship (QSAR) predictor. It was found a significant difference between the binding capabilities of these antigenic peptides to HLA-DR and to HLA-DP/-DQ; the former showed a generally higher affinity than the latter with p-value of 0.02 obtained from 2-tailed Student's t-test. The computational findings were then confirmed by HLA II-peptide stability assay, which demonstrated that the AR allergen-derived peptides have a high in vitro selectivity for HLA-DR over HLA-DP/-DQ. Thus, the HLA-DR isotype, rather than HLA-DP and -DQ, is expected to associate with the pathological process of AR.

The clinical significance of the MIF homolog d-dopachrome tautomerase (MIF-2) and its circulating receptor (sCD74) in burn

BACKGROUND

We reported earlier that the cytokine macrophage migration inhibitory factor (MIF) is a potential biomarker in burn injury. In the present study, we investigated the clinical significance of the newly discovered MIF family member d-dopachrome tautomerase (DDT or MIF-2) and their common soluble receptor CD74 (sCD74) in severely burned patients.

METHODS

DDT and sCD74 serum levels were measured 20 severely burned patients and 20 controls. Serum levels were correlated to the abbreviated burn severity index (ABSI) and total body surface area (TBSA) followed by receiver operating characteristic (ROC) analysis. Data were supported by gene expression dataset analysis of 31 burn patients and 28 healthy controls.

RESULTS

CD74 and DDT were increased in burn patients. Furthermore, CD74 and DDT also were elevated in septic non-survivors when compared to survivors. Serum levels of DDT showed a positive correlation with the ABSI and TBSA in the early stage after burn, and the predictive character of DDT was strongest at 24h. Serum levels of CD74 only correlated with the ABSI 5 days after injury.

CONCLUSIONS

DDT may assist in the monitoring of clinical outcome and prediction of sepsis during the early post-burn period. Soluble CD74 and MIF, by contrast, have limited value as an early predictor of death due to their delayed response to burn.

Immune evasion of microsatellite unstable colorectal cancers

Colorectal cancers (CRC) develop through 2 major pathways of genetic instability. In contrast to the majority of CRCs, which are characterized by chromosomal instability, high-level microsatellite unstable (MSI-H) CRCs arise as a consequence of the loss of DNA mismatch repair (MMR) functions and show accumulation of insertion and deletion mutations particularly in microsatellite sequences. MSI-H occurs in about 15% of CRCs, and virtually all CRCs occurring in the context of the hereditary cancer-predisposing Lynch syndrome. These tumors are characterized by a comparably good prognosis and a low frequency of distant metastases. Because of the expression of a defined set of tumor-specific antigens, MSI-H CRCs elicit a strong local and systemic antitumoral immune response of the host and therefore use different strategies to evade the control of the immune system. In this review, we will summarize novel molecular mechanisms that at the same time drive pathogenesis, immunogenicity and immune evasion during the development and progression of MSI-H CRCs. We will focus on the current knowledge about alterations in human leukocyte antigen (HLA) antigen presentation and discuss how immune evasion-while offering protection against local antitumoral immune responses-paradoxically might interfere with the ability of the tumor to form distant organ metastases.

HLA-DR expression is associated with better prognosis in sporadic Australian clinicopathological Stage C colorectal cancers

Predicting patient outcome for colorectal carcinoma (CRC) with lymph node but not distant metastases remains challenging. Various prognostic markers have been identified including microsatellite instability (MSI) and possibly expression of the MHC Class II protein, HLA-DR. About 15% of sporadic CRC exhibits MSI associated with methylation of the DNA mismatch repair gene hMLH1 promoter. In addition, a significant proportion of unselected CRC demonstrates expression of HLA-DR. We sought to examine the relationship between HLA-DR expression, MSI status and prognosis in sporadic Australian Clinicopathological (ACP) Stage C CRC. Two hundred seventy consecutive patients with sporadic ACP Stage C CRC were treated at Concord Repatriation General Hospital between 1986 and 1992. None of these patients received adjuvant chemotherapy and all were followed for a minimum of 5 years or until death. DNA was extracted from paraffin sections and MSI status determined by PCR. HLA-DR expression was determined immunohistochemically using an antibody against the HLA-DR alpha chain. MSI status could be assigned in 235 cases: 176 CRCs (74.9%) were microsatellite stable, whereas 23 (9.8%) had high levels of MSI (MSI-H) and 36 (15.3%) had low levels of MSI (MSI-L). HLA-DR expression by CRC cells was seen in 148 (60.1%) cases and correlated with the presence of tumor-infiltrating lymphocytes (p = 0.0005) and peritumoral lymphocytes (p = 0.003), but not other clinicopathological features or MSI status. HLA-DR-positive CRCs were strongly associated with better patient outcome (p < 0.0001).

CD74 in antigen presentation, inflammation, and cancers of the gastrointestinal tract

CD74 is a protein whose initial role in antigen presentation was recognized two decades ago. Recent studies have revealed that it has additional functions as a receptor for macrophage migration inhibitory factor and as a receptor for an important human pathogen, Helicobacter pylori (H pylori). The role of CD74 as a receptor is important because after binding of migration inhibitory factor or H pylori, NF-κB and Erk1/2 activation occurs, along with the induction of proinflammatory cytokine secretion. This review provides an up-to-date account of the functions of CD74 and how it might be involved in inflammation and cancer within the gastrointestinal tract.

Induction of apoptosis and immune response by all-trans retinoic acid plus interferon-gamma in human malignant glioblastoma T98G and U87MG cells

Glioblastoma is the most common and highly malignant brain tumor. It is also one among the most therapy-resistant human neoplasias. Patients die within a year of diagnosis despite the use of available treatment strategies such as surgery, radiotherapy, and chemotherapy. Thus, there is a critical need to find a novel therapeutic strategy for treating this disease. Here, we have investigated the molecular mechanisms for induction of apoptosis as well as for activation of immune components in human malignant glioblastoma T98G and U87MG cells following treatment with all-trans retinoic acid (ATRA) plus interferon-gamma (IFN-gamma). Treatment of glioblastoma cells with ATRA alone prevented cell proliferation and induced astrocytic differentiation, while IFN-gamma alone induced apoptosis and modulated expression of human leukocyte antigen (HLA) class II molecules such as HLA-DRalpha, HLA-DR complex, invariant chain (Ii), HLA-DM (an important catalyst of the class II-peptide loading), and gamma interferon-inducible lysosomal thiol-reductase (GILT). Interestingly, both T98G and U87MG cells showed more increase in apoptosis with expression of the HLA class II components for an effective immune response following treatment with ATRA plus IFN-gamma than with IFN-gamma alone. Apoptotic mode of cell death was confirmed morphologically by Wright staining and biochemically by measuring an increase in caspase-3 activity. While conversion of tumor cells into HLA class II+/Ii- cells by stimulation with the helper CD4+ T cells is thought to be challenging, this study reports for the first time that treatment of glioblastoma cells with ATRA plus IFN-gamma can simultaneously enhance apoptosis and expression of the HLA class II immune components with a marked suppression of Ii expression. Taken together, this study suggests that induction of apoptosis and immune components of the HLA class II pathway by ATRA plus IFN-gamma may be a promising chemoimmunotherapeutic strategy for treatment of human malignant glioblastoma.

Human Leukocyte Antigen and Antigen Processing Machinery Component Defects in Astrocytic Tumors

PURPOSE

To determine the frequency of abnormalities in human leukocyte antigen (HLA) and antigen processing machinery (APM) component expression in malignant brain tumors. This information may contribute to our understanding of the immune escape mechanisms used by malignant brain tumors because HLA antigens mediate interactions of tumor cells with the host's immune system.

EXPERIMENTAL DESIGN

Eighty-eight surgically removed malignant astrocytic tumors, classified according to the WHO criteria, were stained in immunoperoxidase reactions with monoclonal antibody recognizing monomorphic, locus-specific, and allospecific determinants of HLA class I antigens, beta2-microglobulin, APM components (LMP2, LMP7, TAP1, TAP2, calnexin, calreticulin, and tapasin), and HLA class II antigens.

RESULTS

HLA class I antigens were lost in approximately 50% of the 47 glioblastoma multiforme (GBM) lesions and in approximately 20% of the 18 grade 2 astrocytoma lesions stained. Selective HLA-A2 antigen loss was observed in approximately 80% of the 24 GBM lesions and in approximately 50% of the 12 grade 2 astrocytoma lesions stained. HLA class I antigen loss was significantly (P < 0.025) correlated with tumor grade. Among the APM components investigated, tapasin expression was down-regulated in approximately 20% of the GBM lesions analyzed; it was associated, although not significantly, with HLA class I antigen down-regulation and tumor grade. HLA class II antigen expression was detected in approximately 30% of the 44 lesions analyzed.

CONCLUSION

The presence of HLA antigen defects in malignant brain tumors may provide an explanation for the relatively poor clinical response rates observed in the majority of the T cell-based immunotherapy clinical trials conducted to date in patients with malignant brain tumors.

Immunology and immunotherapy of colorectal cancer

This review critically discusses data on immunology of colorectal cancer, starting from pathology and molecular biology, and then considering the molecular characterisation of colon cancer antigens and the clinical trials of immunotherapy. A careful evaluation of histopathological studies on intra-epithelial infiltration by T cells in primary tumours, together with the analysis of HLA expression by colorectal cancer cells, suggest that anti-tumour T cell immune responses may take place in vivo in those patients, influencing prognosis and shaping the tumour immunological profile. Moreover, the molecular characterisation of tumour antigens expressed by colorectal carcinomas, together with improved understanding of mechanisms of the immune response and more sensitive methods for the in vivo detection of T cell responses, are now allowing researchers to design new and more effective vaccination protocols, with encouraging preliminary results. By drawing together the experimental evidence from different research fields, this review provides support for the concept that colorectal carcinoma is immunogenic and may reasonably be considered as a target for immunotherapy, and attempts to address critical issues and envisage future developments in this challenging research field.

Survival in human colorectal cancer correlates with expression of the T-cell costimulatory molecule OX-40 (CD134)

BACKGROUND

The T-cell costimulatory molecule OX-40 (CD134) is expressed on activated CD4(+) ("helper") T cells. Such cells have been detected in human cancers, and engagement of OX-40 improves colon cancer immunity in an animal model.

METHODS

Sections of primary colon cancers, normal margins, mesenteric lymph nodes, and metastases were stained for OX-40 by immunohistochemistry. Cancer registry data were reviewed.

RESULTS

High levels of OX-40 positive tumor-infiltrating lymphocytes were found in 15 of 72 primary tumors. Thirty-one cases had prominent lymphocytic infiltrates expressing OX-40 at the invasive margin of the tumor. Overall, 50% of primary tumors showed high expression of OX-40. Nearly all mesenteric lymph nodes expressed OX-40, whether tumor was present or not. Normal margins of colon did not show high levels of OX-40. High OX-40 expression in the primary tumor correlated with better survival (mean survival high OX-40, 47 months, low OX-40, 35 months, P <0.05), although this correlation was not stage-independent.

CONCLUSIONS

High levels of OX-40 positive lymphocytes are present in half of primary colon cancers, and this expression in primary tumors significantly correlates with better survival. This correlation with survival and our previous preclinical research suggest a basis for an OX-40 immunotherapy trial.

The prognostic value of invariant chain (Ii) and Her-2/neu expression in curatively resected colorectal cancer

BACKGROUND

Current methods to predict outcome for patients with curatively resected colorectal cancer are not ideal. The combined use of molecular markers and clinicopathologic features may better identify patients who are at risk for recurrence. The Her-2/neu and invariant chain molecules may be important in cancer development and progression, but their usefulness as clinical predictors of outcome in colorectal cancer has not been well studied.

METHODS

We used immunohistochemistry to determine the expression of Her-2/neu, invariant chain, p27, and p53 in primary tumor samples from 156 patients with curatively resected stage I-III colorectal cancer. The association between expression and clinical outcomes was assessed by univariate and multivariate analysis.

RESULTS

Her-2/neu expression was detected in only 24% of cases, and high levels of invariant chain were detected in only 15%. Although patients whose tumors overexpressed Her-2/neu survived longer than those with non-overexpressing tumors, neither Her-2/neu nor invariant chain were independently associated with survival. Consistent with previous reports, high p27 expression was associated with improved outcome, whereas overexpression of p53 was associated with worse outcome.

CONCLUSIONS

Our study did not reveal a statistically significant association between Her-2/neu or invariant chain expression and clinical outcomes in patients with curatively resected colorectal cancer. However, the data suggest that Her-2/neu could be a favorable prognostic variable. Because of the low frequency of Her-2/neu expression, larger numbers of patients need to be studied for this question to be adequately answered.

Expression of invariant chain (CD 74) and major histocompatibility complex (MHC) class II antigens in the human fetus

During the initiation of an immune response, antigen-presenting cells employ MHC class II antigens as key molecules to present small peptides to CD4-positive lymphocytes. The invariant chain (Ii; CD74) plays a critical role in this process by influencing the expression and peptide loading of the MHC class II molecules. Therefore, coordinate expression of these molecules is believed to play an important role in antigen presentation. This study explores the expression of these molecules in fetal tissues. Formalin-fixed, paraffin-embedded multi-organ tissue blocks from aborted fetuses (age range 7-22 weeks) were immunostained for Ii/CD74 and MHC class II antigens using commercially available monoclonal antibodies for Ii/CD74 (LN2) and MHC class II antigens (LN3), respectively. Coordinate staining for Ii/CD74 and MHC class II antigens was seen in the skin, proximal renal tubules, tips of small intestinal mucosa, and cells of the reticuloendothelial system, including the spleen and thymus. Expression of Ii/CD74, but not of MHC class II antigens, was seen in pulmonary alveolar epithelium in all cases and in testicular Leydig cells (11 of 11 testes examined). The distribution and intensity of staining did not change significantly with age. In conclusion, this study describes distribution of Ii/CD74 and MHC class II antigens in human fetal tissues. Coordinate expression of Ii/CD74 and MHC class II antigens was identified in most fetal tissues, but there were also notable exceptions. In all cases this took the form of expression of Ii/CD74 in the absence of MHC class II expression. Discordance was particularly striking in pulmonary alveolar epithelium and testicular Leydig cells. This suggests that the Ii/CD74 molecule has functional roles in addition to its role in antigen presentation.

Loss of MHC class II expression is associated with a decrease of tumor-infiltrating T cells and an increase of metastatic potential of colorectal cancer: immunohistological and histopathological analyses as compared with normal colonic mucosa and adenomas

We immunohistologically investigated 76 cases of primary colorectal cancer and 13 cases of adenoma to clarify the relationship of MHC class II expression with the grade of differentiation, the density of tumor-infiltrating lymphocytes, and the incidence of metastasis to lymph nodes. MHC class II expression was mostly negative in normal colonic epithelium. In contrast, 32 out of 76 cases (42%) of cancer and five out of 13 cases (38%) of adenoma were positive for MHC class II. MHC class II expression was higher in well-differentiated than in poorly differentiated adenocarcinoma. The density of infiltrating lymphocytes was higher in cancer than in the normal mucosa, and higher in MHC class II-positive tissues than in negative lesions. The incidences of lymphatic invasion and cancer metastasis to lymph nodes were definitely higher in MHC class II-negative cancers than in MHC class II-positive cancers. MHC class II was rarely expressed in metastatic cancer cells of lymph nodes. These results indicated that the loss of MHC class II is correlated with the incidence of metastasis to regional lymph nodes.

Immunoreactivity for LN2 and LN3 distinguishes small cell carcinomas from non-small cell carcinomas in the lung

Immunoreactivity to LN2 and LN3, monoclonal antibodies that recognize components of the class II major histocompatibility complex, was assessed in 72 cases of non-small cell lung carcinoma (NSCLC) (32 biopsy specimens, 40 resection specimens) and 64 cases of small cell carcinoma (56 biopsy specimens, 8 resections) of the lung. All cases were reviewed independently by three pathologists for histological classification. Only 1 of the 64 small cell carcinomas showed immunoreactivity for LN2, and none of the 64 cases showed reactivity for LN3. Among the non-small cell carcinomas, 25 of 48 cases were positive for LN2 and 43 of 71 were positive for LN3; the sensitivity was greater for adenocarcinoma (78.5%) than for squamous cell carcinoma (37%). A combined sensitivity of 64.7% was observed when the results of LN2 and LN3 were combined, and this sensitivity was not significantly diminished in the biopsy subset of cases (59.4%). Differentiation within histological subtypes of NSCLC (ie, well, moderate, or poorly differentiated) did not alter test sensitivity. In conclusion, LN2 and LN3, used alone or in combination, appear highly specific for non-small cell carcinoma and moderately sensitive in both biopsy and resection specimens; therefore, these antibodies may be diagnostically useful in distinguishing small cell from non-small cell carcinoma of the lung.

K-ras mutations and HLA-DR expression in large bowel adenomas

A total of 72 sporadic colorectal adenomas in 56 patients were studied for the presence of point mutations in codons 12 and 13 of the K-ras gene and for HLA-DR antigen expression related to clinicopathological variables. Forty K-ras mutations in 39 adenomas were found (54%): 31 (77%) in codon 12 and nine (23%) in codon 13. There was a strong relationship between the incidence of K-ras mutations and adenoma type, degree of dysplasia and sex. The highest frequency of K-ras mutations was seen in large adenomas of the villous type with high-grade dysplasia. Fourteen out of 15 adenomas obtained from 14 women above 65 years of age carried mutations. HLA-DR positivity was found in 38% of the adenomas, large tumours and those with high-grade dysplasia having the strongest staining. Coexpression of K-ras mutations and HLA-DR was found significantly more frequently in large and highly dysplastic adenomas, although two-way analysis of variance showing size and grade of dysplasia to be the most important variable. None of the adenomas with low-grade dysplasia showed both K-ras mutation and HLA-DR positivity (P = 0.004). K-ras mutation is recognised as an early event in colorectal carcinogenesis. The mutation might give rise to peptides that may be presented on the tumour cell surface by class II molecules, and thereby induce immune responses against neoplastic cells.

Immunohistochemically demonstrated expression of HLA-DR antigen in colorectal adenocarcinomas and its relation to clinicopathological features

We studied 148 colorectal adenocarcinomas to clarify any correlation between HLA-DR antigen expression on tumor cells and histopathological features. Paraffin sections of formalin-fixed tissues were stained with HLA-DR antigen using the indirect immunoperoxidase technique. All the tumor tissues were divided into two groups, depending on the incidence of HLA-DR-positive cells (greater and lesser than 50%). Carcinoma tissues with a higher incidence showed less mural invasion, lymphoductal invasion, venous invasion, lymphonodular metastasis, and peritoneal metastasis. Tissues with a high HLA-DR reactivity were more often observed for Dukes' A and B stages, whereas those with a low HLA-DR positivity were frequently Dukes' C and D stages. As for the cumulative survival rate, the group with high HLA-DR expression demonstrated significantly better survival. We speculate that HLA-DR expression by colorectal cancer cells exerts a favorable influence on clinical course.

Expression of APO-1 (CD95), a member of the NGF/TNF receptor superfamily, in normal and neoplastic colon epithelium

APO-1 is a 48-kDa cell-membrane protein identical to the Fas antigen now designated CD95. It is a member of the NGF/TNF receptor superfamily. Anti-APO-1 monoclonal antibody induces apoptosis in a variety of cell types expressing this antigen. We immunohistochemically investigated APO-1 expression in normal colon mucosa, 20 adenomas, 258 colon carcinomas and 10 liver metastases and carried out in vitro studies using a panel of colon-carcinoma cell lines. Immunohistochemically, APO-1 was regularly expressed at the basolateral membrane of normal colon epithelia. In a minor fraction of colon adenomas and in 39.1% of colon carcinomas APO-1 expression was diminished and in 48.1% of carcinomas, predominantly of the non-mucinous type, APO-1 expression was completely abrogated. The normal level of APO-1 in carcinomas was correlated with the mucinous type. Reduced/lost APO-1 expression was more frequent in rectal carcinomas. Complete loss of APO-1 was more frequent in tumors that had already metastasized. APO-1 expression in liver metastases essentially corresponded to that of the primary tumors. Comparative analysis with data from previous studies revealed that the mode of APO-1 expression is correlated with that of HLA-A,B,C./beta 2m, HLA-DR, HLA-D-associated invariant chain and of the secretory component. Surface expression of APO-1 was heterogeneous in colon-carcinoma cell lines; SW480 expressed considerable amounts of APO-1 on all cells, while HT-29 constitutively did less so and only in a minority of cells. Surface density of APO-1 and the fraction of positive cells in HT-29 was enhanced by interferon-gamma (IFN-gamma) and, additively, by tumor necrosis factor-alpha (TNF-alpha), whereas in SW480 APO-1 expression was not modulated by these cytokines. We conclude that neoplastic transformation of colon epithelium often leads to a loss of the physiologic, high level of surface APO-1 by giving rise either to a stable lack of APO-1 or to an IFN-gamma/TNF-alpha-sensitive phenotype of inducible APO-1 expression.

Strong HLA-DR expression in large bowel carcinomas is associated with good prognosis

One hundred large bowel carcinomas operated on between 1978 and 1982 were studied immunohistochemically with regard to expression of HLA-DR antigens. Three sections from each tumour were investigated by a semiquantitative scoring system, and a mean score for each patient established. Based on this scoring system, the tumours were divided into three groups: 0; 0.1-1.0; and > 1.0. All patients were followed until death (n = 68) or until June 1, 1992, and all cancer-specific deaths (n = 56) have been recorded. Analysis of survival in the whole patient group showed significant difference between the three levels of tumour HLA-DR expression (P = 0.006); patients who had tumours with strong HLA-DR expression showing the best survival. In a stratified analysis after Dukes' stages there was still a significant difference (P > 0.001) between the three levels of HLA-DR staining intensity. After a multiple regression analysis (Cox) with correction for different variables, the HLA-DR expression maintained its significance as a risk factor. To our knowledge this is the first time a relationship between intensity of tumour DR expression and survival has been shown in large bowel carcinoma.

Dendritic cells in glomerulonephritis

Renal biopsies (n = 45) from patients with various forms of glomerulonephritis (GN), comprising mesangial IgA-GN (n = 25), focal glomerular sclerosis (n = 13) and acute GN (n = 7), were examined by double staining immunocytochemistry (APAAP, streptavidin-peroxidase) using unconjugated monoclonal antibodies (Ab) against--(i) the CD1b antigen expressed on dendritic cells (DCs), (ii) the invariant chain (Ii), and (iii) biotin-conjugated Ab against HLA-DR. In normal control kidneys (n = 7) without interstitial inflammation, CD1b-positive DCs were not detected. Glomerular endothelial cells and a few cells in mesangial areas showed double staining with the Ab against HLA-DR in Ii. In GN without active interstitial inflammation (n = 9), CD1b-positive DCs were not found. In biopsies with interstitial inflammation (n = 36) CD1b-positive DCs were found interspersed among other inflammatory cells. In seven of the biopsies showing IgA-GN DCs were seen in the vicinity of those glomeruli that exhibited either crescents or glomerular sclerosis with splitting of Bowman's capsule. In proximal tubular epithelial cells de novo expression of HLA-DR/Ii-chain was only seen when DCs were present. We conclude that in different forms of GN: (i) CD1b-positive DCs play an important role in the development of interstitial inflammation, and (ii) their presence may be related to the de novo coexpression of HLA-DR/Ii in tubular epithelial cells, possibly mediated through the production of interferon gamma and other cytokines.

Expression of intercellular adhesion molecule 1 (ICAM-1) during the development of invasion and/or metastasis of gastric carcinoma

In this study, using two-color flow-cytometric analysis, we examined the expression of histocompatibility locus antigens (HLA) classes I and II, and intercellular adhesion molecule 1 (ICAM-1) in 10 cases of normal gastric mucosa, 13 cases of primary carcinoma on the stomach, 16 cases of metastatic carcinoma from malignant ascites in patients with gastric carcinoma and 14 samples of their cultured carcinoma cells. Compared with normal gastric mucosa, HLA class I were highly expressed in a considerable number of tumor cells in each experimental group. The expression of HLA class II tended to reduce in the order of normal gastric mucosa, primary gastric carcinoma and peritoneal-effusion-associated carcinoma. Altogether, 85.7% of cases of cultured tumor cells showed abrogation and loss of HLA class II. The ICAM-1 molecule was not detected on normal gastric epithelial cells. In few cases, carcinoma cells from large volumes of tumor located in the stomach showed detectable amounts of ICAM-1. On the other hand, all of the metastatic carcinoma cells from peritoneal effusions showed a high level of expression of the ICAM-1 molecule. The expression of ICAM-1 on adenocarcinoma cells was maintained and/or augmented by in vitro cultivation with tumor-infiltrating lymphocytes (TIL). Furthermore, two-color fluorescence-activated cell sorting analysis of TIL revealed that significant correlation was observed between the expression of ICAM-1 and the degree of TIL, composed mainly of CD3+ T cells including CD8+CD11b-, CD8+CD28+, CD8+S6F1+ and CD4+Leu8+, and CD57+CD16- and CD57+CD16+ NK cells, and HLA-DR+LeuM3+ macrophages.

Analysis of epithelial and lymphoid phenotypic markers in relation to growth pattern of colorectal adenomas

The relationship of villous to tubular adenomas is poorly understood and often difficult to characterize morphologically. A villous growth pattern in colorectal adenomas has been associated with a higher frequency of high-grade dysplasia. We compared phenotypic markers using immunoperoxidase techniques in paired samples of villous (75% to 100% villous) and pure tubular adenomas matched for size and degree of dysplasia, which were selected by review of 1,000 polyps from our files. The following monoclonal antibodies were used: CAM 5.2 and AE1/AE3 to cytokeratins; B18, D14, B7.1, and B7.8 to four distinct carcinoembryonic antigen epitopes; Leu-M1 and LN3 to HLA-DR antigen; LN2 to invariant chain class II major histocompatibility complex; LN1 and MB2 to B-cell markers; UCHL1 and MT1 to T-cell markers; Leu-7 to natural killer cells; Mac 387 to macrophages; S-100 to Langerhans-type cells; and a polyclonal antibody to secretory component. LN3 reactivity correlated with villous morphology and secretory component correlated with tubular morphology. Combined HLA-DR and secretory component expression discriminated between tubular and villous growth patterns in 12 of 15 pairs of adenomas (P less than .001). LN2 was expressed more frequently than LN3, but did not correlate with growth pattern. Neuroendocrine cells (Leu-7) were more frequent in tubular adenomas. Carcinoembryonic antigen epitopes did not relate to growth pattern. We did not confirm previously reported differences in cytokeratin expression. We concluded that among the markers tested, HLA-DR expression, which may have an immunologic basis, is most characteristic of colorectal adenomas that exhibit a villous growth pattern.

Expression of MHC class II antigens (HLA-DR, -DP, and -DQ) on human gastric epithelium

Class II antigen expression on gastric epithelium was investigated using an immunoperoxidase method in relation to the degree of inflammatory cell infiltration in the lamina propria. Sixty-six biopsy specimens from 43 patients with chronic gastritis were examined. The frequency of HLA-DR expression in specimens with cell infiltration was 94%, while that in specimens without cell infiltration was 24%. There was significant difference in the frequency of HLA-DR expression between the two groups (P less than 0.01). HLA-DR was most intensely expressed in the glandular neck portion. The frequency and extent of class II antigen expression on gastric epithelium with cell infiltration were in the following order: DR greater than DP greater than DQ. The extent of DR and DP, but not DQ expression generally paralleled the degree of cell infiltration. Intestinal metaplasia was found in 13 specimens. In the area of intestinal metaplasia, epithelial class II staining was absent except for one specimen. These results suggest that the respective genes of three class II antigens are regulated by different mechanisms and that an immunological mechanism plays a role in the pathogenesis of gastritis.

Class II antigen-associated invariant chain mRNA in mouse small intestine

MHC class II antigen-associated invariant (Ii) chain mRNA appears in mouse small intestine during postnatal development. Ii chain cDNA hybridizes to RNA from epithelial sheets dissociated from the lamina propria with EDTA. Of several mouse organs tested, only bone marrow and spleen contain higher levels of Ii chain mRNA than small bowel. Ii chain mRNA is not detected in stomach, colon, duodenum, testis, liver, submandibular gland, or L-cell RNA; brain contains a cross-reactive but uncharacterized sequence. cDNA amplification using primers specific for both Ii31 and Ii41 chain mRNAs showed that both forms occur in small intestine. These results support the conclusion that regulation of the class II Ii chain gene is associated with the ontogeny of intestinal immunity.

Sporadic loss of leucocyte-function-associated antigen-3 (LFA-3) in colorectal carcinomas

Leucocyte-function-associated antigen-3 (LFA-3) is a cell surface glycoprotein involved in T-cell/target cell interaction. The expression of LFA-3 on the cell surface was found to be inevitably associated with the expression of HLA molecules. Loss of LFA-3 or HLA proteins on tumour cells might result in ineffective T-cell/target cell interaction and a failure of immunological tumour surveillance. Immunohistochemistry revealed that LFA-3 is expressed in normal colonic epithelium; however, in a minor fraction of colonic adenomas and in 50.3% of colorectal carcinomas LFA-3 expression was reduced or even absent. To investigate whether the presence or absence of LFA-3 in colorectal carcinomas influences the relapse rate and time of tumour-related death, 149 patients who underwent putatively curative surgery were surveyed for a maximum of 65 months (mean 48 months). In contrast to the prognostic role of tumour stage and grade, the presence versus absence of LFA-3 was not correlated with recurrence or survival. Regarding survival and growth of residual tumour cells after potentially curative resection of the initial tumour burden, we conclude that the status of LFA-3 expression in colorectal carcinoma seems to be irrelevant in vivo.

Expression of HLA-DR and secretory component antigens and lymphocyte infiltration in human gastric nonmalignant and malignant tissues: an immunohistochemical study

The relation between HLA-DR and secretory component (SC) expression and the degree of lymphocyte infiltration was immunohistochemically examined in human gastric mucosa with or without intestinal metaplasia and gastric carcinoma tissues. Gastric mucosa without obvious inflammation showed neither expression of HLA-DR or SC nor remarkable lymphoid infiltration. In contrast, gastric mucosa with chronic inflammation, tissues with incomplete type of intestinal metaplasia, and carcinoma demonstrated both HLA-DR and SC in almost the same area and also prominent lymphoid infiltration in the surrounding stroma. This simultaneous expression of HLA-DR and SC was not observed in complete type of intestinal metaplasia. The results indicate a close relationship between expression of HLA-DR and SC and the presence of lymphocyte infiltration in gastric mucosa, areas of incomplete type of intestinal metaplasia and in gastric carcinomas.

Distribution of Langerhans cells and HLA class II molecules in prostatic carcinomas of different histopathological grade

We have investigated Langerhans cell (LC) distribution in 38 prostatic carcinomas, of various degrees of differentiation, by immunohistochemistry with a polyclonal anti-S-100 serum, furthermore evaluating the expression of HLA class II-DR by neoplastic cells using a monoclonal antibody (MoAb) that reacts with a monomorphic determinant in formalin-fixed paraffin-embedded tissue. Antiserum to S-100 protein identified LCs mostly in carcinomas ranging from grade 1 to grade 2, while LCs were inconspicuous in grade 4 and virtually absent in grade 5 cancers. Moreover, sections stained with the anti -HLA-DR MoAb displayed an immunoreactivity, both cytoplasmic and apical, especially confined to neoplastic glands of low grade (1-2) carcinomas. Although we did not find a direct correlation between the two parameters under investigation and lymphoid infiltrate, we were able to document an increased number of HLA class II-positive interstitial cells in low-grade carcinomas, corresponding mostly to macrophages. Our results indicate that LC number is inversely correlated to the histopathological grade and directly to the expression of HLA class II-DR molecules by tumor cells; we believe that this might be important in understanding the more favorable biological behavior of low-grade prostate carcinomas as opposed to the higher grades, since LCs and HLA class II molecules may provide a means of eliciting the immune response, both LCs and epithelial cells expressing HLA class II molecules being capable of direct antigen presentation to immune cells. In this context macrophages might play a primary role in controlling tumor progression. To the best of our knowledge this is the first time that an attempt is made to correlate LCs and HLA class II expression to histopathological grading of prostatic carcinomas. We would also suggest that the presence of LCs and HLA class II molecules, either singly or in combination, in carcinoma of the prostate represents a good prognostic indicator, being constantly associated with the clinically less aggressive low-grade tumors. The evaluation of these two parameters might prove useful in the assessment of intermediate grades where no valid histologic criteria have been found to predict the clinical course of the disease.

Frequency of abnormal expression of HLA-A,B,C and HLA-DR molecules, invariant chain, and LFA-3 (CD58) in colorectal carcinoma and its impact on tumor recurrence

HLA-A,B,C and HLA-DR molecules are involved in cognate LFA-3 (CD58) in antigen-independent T-cell/target-cell interaction. T-cell-mediated host-versus-tumor response might therefore depend on the presence of both types of molecules on the surface of the target cell. To investigate whether presence or absence of these molecules in colorectal carcinoma influences the recurrence rate, 149 patients who underwent curative surgery were surveyed for a maximum of 65 months (mean, 48 months). As determined by immunohistochemistry, aberrant reduction of HLA-A,B,C determinants was observed in 34.9 and a complete loss in 8.7% of the tumor specimens. An induction of HLA-DR molecules was found in 55.0 and of the HLA-DR-associated invariant chain (Ii) in 81.9%. An abnormal reduction of LFA-3 was detected in 43.6%, while a complete loss of this structure was observed in 6.7%. Reduction/loss of HLA-A,B,C was correlated with reduction/loss of LFA-3 (p = 0.03). In contrast to the prognostic role of tumor stage and grade, the presence vs. absence of all these structures was not correlated with the recurrence rate. We conclude that, although encoded on different chromosomes, an abnormal reduction/loss of HLA-A,B,C and LFA-3 might be the consequence of one transacting down-regulating signal. However, the resulting deviant immunophenotypes do not profoundly influence survival and growth potential of residual tumor cells.

Expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, -DQ and of HLA-D-associated invariant chain (Ii) in soft-tissue tumors

Non-neoplastic mesenchymal cells, along with 33 benign and 87 malignant soft-tissue tumors (STT) were examined for expression of HLA-A,B,C, beta 2-microglobulin (beta 2m), HLA-DR, -DP, and -DQ molecules and the HLA-D associated invariant chain (Ii). Serial frozen sections were immunostained using monoclonal antibodies (MAbs) to monomorphic framework determinants of HLA sublocus products, beta 2m and Ii, and to CD53, a recently defined broadly distributed pan-leucocyte molecule. Compared with the normal state, an induction/neo-expression of HLA-A,B,C/beta 2m was found in a considerable number of tumors of muscle, peripheral nerve, cartilage-forming, adipose, and vascular tissues. Conversely, some tumors of fibrous origin and of autonomic ganglia showed an abnormal abrogation/loss of HLA-A,B,C/beta 2m with respect to their cells of origin. Small, round tumor cells present in various types of STT exhibited a heterogenous pattern of expression of these molecules with a preponderance of HLA-A, B,C/beta 2m-negativity. HLA-D/Ii determinants were rarely detectable in STT. Besides their expression in some fibrohistiocytic tumors, they were only occasionally found in tumors of smooth-muscle, peripheral-nerve and vascular origin as well as in one clear-cell sarcoma. In all tumors but one, there was no microtopographic association between HLA-D/Ii-positive tumor cells and inflammatory cells. CD53 allowed discrimination between dendritic interstitial cells (DIC) and neoplastic cells and additionally revealed that, in contrast to other solid tumors, STT are generally characterized by an extreme scarcity of lymphohistiocytic infiltrates. Our data indicate that, aside from very rare exceptions, aberrant induction or abrogation of MHC molecules in STT occurs in the absence of lymphohistiocytic stromal infiltrates, suggesting that these alterations might not be a consequence of local cytokine effects.

Class II (HLA-DR, -DP, and -DO) antigens on intestinal epithelia in ulcerative colitis, Crohn's disease, colorectal cancer and normal small intestine

Class II antigens in involved colonic epithelia of ulcerative colitis (UC), Crohn's disease (CD), colorectal cancer, and epithelia of normal small intestine were investigated using an immunoperoxidase method. Ten normal colonic mucosa served as normal controls. Ten specimens were studied for each group. Normal colonic epithelia did not express class II antigens. In colonic diseases; (1) with regard to the frequency and extent of class II antigens on epithelia. HLA-DR antigens were the most highly and greatly expressed, followed by HLA-DP and then HLA-DQ antigens. (2) The extent of HLA-DR and -DP, but not HLA-DQ, expression on epithelia of UC and colorectal cancer seemed to be positively correlated with the degree of mononuclear cell infiltration in the lesion. (3) The extent of class II antigen expression on colonic epithelia in CD was not related to the degree of mononuclear cell infiltration in the lesion. (4) The extent of HLA-DR and -DP expression on epithelia of colorectal cancer seemed to be positively correlated with increasing undifferentiation. In the normal small intestine, where HLA-DR antigens were physiologically expressed on epithelia. HLA-DQ antigens were not expressed. The heterogeneity among colonic diseases, and between the physiological and pathological status, may reflect differences in immunoregulation.

Correlation of HLA-D/Ii antigen expression in breast carcinoma with local lymphohistiocytic infiltration reveals considerable dysregulation in a subset of tumors

Non-neoplastic mammary glands and 203 carcinomas of the breast were examined immunohistochemically for expression of HLA-DR, -DP, and -DQ molecules and the HLA-D-associated invariant chain (Ii). According to the reaction of normal breast epithelium in the course of chronic inflammation, these antigens were found to be induced in 120 carcinomas. In 106 of these the order was Ii greater than or equal to HLA-DR greater than or equal to HLA-DP greater than or equal to HLA-DQ. The extent of induction of these sequentially expressed antigens correlated with the density of local lymphohistiocytic infiltration (Ii: p = 0.003; HLA-DR: p = 0.0005; HLA-DP: p = 0.0000005; HLA-DQ: p = 0.01). Therefore, Ii/HLA-D antigen expression of carcinoma cells in local association with inflammation was regarded as an adequate reaction. The presence of these antigens in the absence of inflammation was regarded as "inadequate hyper-expression", and was found in 14 cases involving Ii, in 8 involving HLA-DR, and in 1 case each involving -DP and -DQ molecules. In contrast, 20 cases expressed minimal/no Ii despite heavy inflammatory infiltration. This "inadequate hypo-expression" was also found in 25 cases involving HLA-DR, in 30 involving -DP and in 40 involving -DQ determinants. Combining the 2 variants showed that at least 54 cases (26.6%) were characterized as being dysregulated. "Adequate vs. inadequate Ii/HLA-D antigen expression" did not correlate with tumor grading and might therefore be an independent parameter.

Phenotypic characterization of alveolar capillary endothelial cells, alveolar epithelial cells and alveolar macrophages in patients with pulmonary fibrosis, with special reference to MHC class II antigens

Major histocompatibility complex (MHC) class II antigens are essential in the presentation of antigens to T lymphocytes, and cells expressing MHC class II antigens are known to play a role as antigen presenting cells (APC). We investigated the distribution of MHC class II antigens and the reactivity of monoclonal antibodies OKM1 and OKM5 in normal and fibrotic lungs immunohistochemically. The results showed that alveolar capillary endothelial cells (ACEnd) expressed MHC class II antigens and were reactive with OKM5 in both normal lungs and the non-thickened parts of alveolar septa of pulmonary fibrosis. However, ACEnd did not express MHC class II antigens and were not reactive with OKM5 in thickened alveolar septa of pulmonary fibrosis. Type II alveolar epithelial cells (AEp) proliferating and replacing type I AEp in pulmonary fibrosis expressed MHC class II antigens strongly. Alveolar macrophages expressed MHC class II antigens strongly and reacted with OKM1 in pulmonary fibrosis, especially in alveolar spaces. These findings suggest that the phenotypic changes of ACEnd may be involved in the process of pulmonary fibrosis, and type II AEp and alveolar macrophages in the parts of thickened alveolar septa may play a role as APC.