Lesional activation of Tc 17 cells in Behçet's disease and psoriasis supports HLA-class I-mediated autoimmune responses

BACKGROUND

Behçet's disease (BD) presents with lymphocytic and neutrophilic vasculitis of unknown aetiology. HLA-B*51 ERAP1 and IL12R/IL23R are genetic risk factors. IL-23 regulates IL-17A, which controls recruitment and activation of neutrophils.

OBJECTIVES

To determine pathological changes in BD skin lesions related to the complex genetic predisposition METHODS: We characterised the expression of IL-17A and IL-23A in various cell types by immunohistological double staining of sections from papulopustular skin lesions (PPL) of acute attacks of BD and lesions of psoriasis vulgaris (PV), another HLA-class I-associated T-cell mediated autoimmune disease in which excessive T-cell derived IL-17A production promotes neutrophil activation.

RESULTS

We found that in BD lesions, as in psoriasis, actively expanding CD8⁺ T cells were the predominant source of IL-17A. IL-17A⁺ CD8⁺ T (Tc17) cells outnumbered infiltrating IL-17A⁺ CD4⁺ T cells. Unlike the epidermal localisation of CD8⁺ T cells in psoriasis, Tc17 cells in BD lesions infiltrated mainly the perivascular tissue and also the blood vessel walls of dermis and subcutaneous tissue. They colocalised with a marked IL-23A expression by CD11c⁺ dendritic cells (DCs) and CD68⁺ macrophages. IL-17A expression was associated with extensive recruitment of neutrophils around blood vessels that formed neutrophil extracellular traps (NETs).

CONCLUSIONS

In BD, the genetic predisposition may mediate antigen-specific activation and differentiation of a T_c 17 response, possibly targeting endothelial antigens. Neutrophils recruited by IL-17A in this process may enhance tissue damage by extensive NET formation (NETosis). Thus, the IL-23/IL-17 axis presumably controls neutrophilic inflammation in BD vasculitis in the context of a predominant antigen-specific CD8⁺ T-cell response.

Prevalence of MCPyV in Merkel cell carcinoma and non-MCC tumors

BACKGROUND

Merkel cell polyomavirus (MCPyV) is the likely causative agent of Merkel cell carcinoma (MCC). However, the prevalence of MCPyV in non-MCC population and its possible role in the pathogenesis of other skin cancers are not known yet.

METHODS

A molecular pathology study was performed in 33 MCC samples and 33 age- and sex-matched samples of sun exposed non-MCC tumors [12 seborrheic keratoses (SK), 11 basal cell carcinomas (BCC) and 10 lentigo maligna melanomas (LMM)]. All tumors were analyzed for presence of MCPyV-DNA by polymerase chain reaction (PCR) and Southern-Blot hybridization of PCR products.

RESULTS

MCPyV sequences were detected in 21 MCC samples (64%) and in 2 non-MCC tumors of sun exposed skin (6%; both SK-patients). Neither the tissue samples from BCC nor LMM proved positive for MCPyV sequences.

CONCLUSION

We were able to confirm prior data on prevalence of MCPyV-DNA in MCC. Furthermore, a female predominance of MCPyV-positive MCC-patients was detected. There was no relevant association of MCPyV with SK, BCC and LMM. Speculative, prevalence of MCPyV in an age- and sex-matched non-MCC population could average up to 6%.

[Immunohistochemical and molecular-pathologic investigations in dermatohistology]

Despite sophisticated diagnostic algorithms, pure morphologic diagnosis has reached its limits in many areas of general and dermatologic pathology, especially in the wake of advances in basic sciences. Modern microscopic diagnosis, especially when evaluating lymphocytic and mesenchymal tumors, depends greatly on identifying the expression of surface markers (for example CD3 as T-cell surface receptor), signal proteins (cyclin D in cell cycle control) or structural proteins in tumor cells (actin in myogenous cells). Molecular biological methods include those techniques which make it possible to identify cellular and extracellular macro-molecules such as proteins and nucleic acids. At the protein level, the selective identification of proteins on sections via immunohistochemical methods is a widely used and essential component of modern pathologic-anatomic diagnosis.

Heterogeneity of T-cell clones infiltrating primary malignant melanomas

It is established that primary malignant melanomas (pMM) can be infiltrated by T-cell populations with predominantly one T-cell clone. As pMM generally express multiple tumor-associated antigens (TAA), here we used laser-capture microdissection (LCM) to isolate different tumor-infiltrating lymphocyte (TIL) clusters in order to determine whether pMM are infiltrated only by one single clone or whether the TAA may attract various T-cell populations. As T-cell receptor (TCR) clonality is a useful tool for the demonstration of specific T-cell clones, we analyzed 56 pMM, three cutaneous melanoma metastases, and 15 pairs of pMM with a sentinel lymph node (SLN) for clonal rearrangements of the (TCR) gamma chain gene. We detected the clonality of TCR gamma chain gene in 25 of 56 pMM, and in 10 of 17 SLN studied. In four of the 15 pairs of primary tumor and SLN, we found clonal TCR gamma in both the melanoma and the SLN, with two pairs harboring the identical clone. As we detected different clones in pMM and the corresponding SLN, we subsequently performed LCM in 21 malignant melanomas with multiple lymphocytic clusters for the presence of focal clonal T cells in different regions of the melanoma. In seven melanomas, both clusters of TILs showed the same rearranged TCR gamma chain gene and in five of the seven biopsies the clonal rearrangement occurred in different variable (V) regions of the TCR gamma chain gene. These tumors showed infiltration by more than one clone. In 10 biopsies TCR clonality was restricted to one cluster, while the second microdissected sample of the infiltrate was polyclonal. In conclusion, within one primary malignant melanoma several T-cell clones with different rearrangements may occur. The balance between these clones may decide on the progress of melanoma.

Laser-capture microdissection: applications in routine molecular dermatopathology

Advances in molecular pathology with the introduction of the Southern blot technique and the polymerase chain reaction (PCR) have emerged as important tools, which are frequently used in routine dermato-histopathology. Applications for PCR-based diagnostics are particularly helpful for the determination of clonality in cutaneous lymphocytic infiltrates and for detection of infectious agents, such as herpes simplex virus (HSV), varicella zoster virus (VZV), Borrelia burgdorferi, Mycobacteria, Leishmania, and Treponema pallidum. As biopsies are always composed of different cells, the cells of interest are often only a minor population. As a consequence, their specific DNA is diluted by the majority of contaminating cells. Another problem is the time- and labor-intensive DNA extraction, because usually only formalin-fixed, paraffin-embedded tissue is available, which makes molecular diagnostics a time and labor consuming, and consequently a cost-intensive procedure. To overcome these shortcomings and to eventually shorten the time to generate a result, we introduce a laser-capture microdissection (LCM)-based method for the detection of infectious agents and clonality. Only the cells of interest for the particular indication are microdissected (e.g. epidermal cells for HSV and VZV and lymphocytes for clonality analysis) and subjected to PCR amplification. Due to an accelerated DNA-extraction procedure which generates DNA in 5 h (compared to 3-4 days using conventional DNA extraction), we are able to generate a result within one working day.

Mutations of the BRAF gene in benign and malignant melanocytic lesions

A single-point mutation in exon 15 of the BRAF gene has recently been reported in a high percentage in cultured melanoma cells and in 6 of 9 primary melanomas examined. To evaluate the impact of the T1796A BRAF mutation, we screened primary melanomas, various types of nevi and lesions where a melanoma developed in an underlying nevus. We could detect the mutation in 28 of 97 (29%) melanomas and in 39 of 187 (21%) nevi, including blue nevi (0/20) and Spitz nevi (0/69), which did not carry the mutation. In melanomas with an underlying nevus, either the mutation was present in both the laser-microdissected nevus cells and the laser-microdissected melanoma cells (3/14) or both lesions were negative for the BRAF mutation except one case. In conclusion, mutations in exon 15 of the BRAF gene are nonspecific for progression of a nevus to a melanoma. Other so far unknown cofactors seem to be of importance.

Improved detection of clonality in cutaneous T-cell lymphomas using laser capture microdissection

BACKGROUND

The diagnosis of cutaneous T-cell lymphoma is a challenge for both the pathologist and the clinician. This is particularly true for distinguishing early-stage mycosis fungoides from dermatitis. In this clinical setting, the presence of a clonal T-cell population supports lymphoma.

METHODS

Usually, routinely processed paraffin-embedded material is available for gene rearrangement analysis, and polymerase chain reaction (PCR)-based methods to assess clonality can be performed. One drawback of this approach is that sensitivity is suboptimal in biopsy specimens in which the lymphocytic infiltrate represents only a small percentage of all cells present. Another drawback is that DNA extraction from routinely processed, paraffin-embedded tissue is a time-consuming and labor-intensive procedure which can take up to 5 days in our laboratory. To bypass these problems, we used laser capture microdissection (LCM) to obtain lymphocytic infiltrates from tissue sections of formalin-fixed, paraffin-embedded skin biopsy specimens. This approach allows for more specific PCR assessment of the lymphocytic infiltrate and for rapid DNA extraction and PCR analysis.

RESULTS

Using the LCM approach, we could demonstrate clonal T-cell receptor gamma gene rearrangements in biopsy specimens that did not show clonality using DNA extracted by conventional methods from full tissue sections. In addition, DNA extraction and PCR analysis can be performed in 11 h.

CONCLUSION

In conclusion, applying LCM to clonality analysis of cutaneous lymphocytic infiltrates is rapid and more sensitive than conventional methods, and we recommend introducing this approach into the routine diagnostic setting.

[In situ PCR and PCR in situ hybridization of paraffin-embedded tissue. New diagnostic possibilities in pathology]

In situ polymerase chain reaction (PCR) and PCR in situ hybridization are new diagnostic tools in dermatopathology. These techniques can combine the sensitivity of PCR with the advantage of in situ hybridization to localize specific cellular structures. With optical control of the PCR reaction product in these techniques, false-positive results due to contamination can be minimized. Several working protocols have been established which allow detection of DNA and RNA sequences in a rapid and reproducible manner. Two different methods have been established to detect the amplification product, the indirect PCR in situ hybridization (PCRisHyb), and the direct in situ PCR (isPCR). An easy and reproducible method for PCRisHyb and isPCR in formalin-fixed and paraffin-embedded tissue is described and the two techniques are compared. Using both isPCR and PCRisHyb, the amplification product can be visualized with an optimal morphological preservation of the tissue. Indirect PCRisHyb showed a slightly higher specificity whereas direct isPCR was the quicker, easier and less expensive method.

Automated high-resolution polymerase chain reaction fragment analysis: a method for detecting T-cell receptor gamma-chain gene rearrangements in lymphoproliferative diseases

Southern blot analysis and the polymerase chain reaction (PCR) are powerful tools for detecting clonal antigen receptor gene rearrangements. However, a number of limitations restrict the predictive value of the results obtained by these techniques as they are commonly used. We describe a new method, automated high-resolution PCR fragment analysis, that can partially overcome many of the limitations of analyzing the T-cell receptor (TCR) gamma-chain gene. Analysis of TCR-gamma is performed using PCR with four sets of primers, previously described by others, specific for all variable (V) and joining (J) regions of the TCR gamma-chain gene. In addition, the four V region primers are 5' end-labeled with a fluorescent compound, 5-carboxyfluorescein. After amplification, the labeled PCR products are separated with an automated sequencing system, ABI 373 (Applied Biosystems, Weiterstadt, Germany). With the help of the Gene-Scan software ABI 672 (Applied Biosystems) and fluorescent-labeled DNA length markers, the exact size of each peak can be displayed and analyzed. The resolution of this method allows separation of PCR products differing in length by as little as 1 bp. Semiquantitative estimation of specific clones also can be performed. Infiltrate-specific gene rearrangement patterns can be identified and recognized in different tissue specimens at the time of diagnosis or in subsequent biopsy specimens. We conclude that automated high-resolution PCR fragment analysis allows more accurate and convenient analysis of the TCR gamma-chain gene.