Humeral head shape as an indicator of locomotor behavior in extant strepsirhines and Eocene adapids

Postcranial material from Notharctus, Smilodectes and Cantius is abundant and well studied, but debate continues over whether the locomotor repertoire of these animals included a substantial component of vertical leaping. Here, the shape of the humeral head of 11 genera of extant strepsirhines, Notharctus, Smilodectes and Cantius was quantified using serial mediolateral and proximodistal contours. Univariate and multivariate analyses of these data show that vertically leaping strepsirhines have a distally relatively high narrow humeral head compared to arboreal quadrupeds and it places Notharctus and Smilodectes in a group with Hapalemur griseus, while Cantius is grouped with Eulemur macaco, suggesting that a quadrupedal form preceded the appearance of vertical leaping.

Differences in reactivity to cyclosporin A and interferon-gamma of normal and HPV-transformed keratinocytes

In humans, cyclosporin A (CsA) avoids organ allograft rejection but induces skin carcinomas after long term immunosuppressive treatment; some of these lesions contain human papillomavirus (HPV) DNA. Interferon-gamma (IFN-gamma) is sometimes used in local treatment of persistent or recurrent lesions in normal population. In vivo, both drugs have an effect on keratinocytes which remains unclear. Therefore, their effect was studied on in vitro models of normal or HPV-transformed epithelial cell cultures. After exposure of proliferating cells for 1-3 days to 0.5-16 micrograms/ml CsA and 5-160 U/ml IFN-gamma, no cytotoxicity was observed; cell growth was inhibited; cell morphology was altered with CsA and cytoplasmic vacuoles were seen in some cells. Changes in the cell cycle were mainly obtained after treatment with 8 micrograms/ml CsA or 160 U/ml IFN-gamma, with an accumulation in S-phase especially in HPV-transformed cells. Thus, CsA and IFN-gamma affected, normal and HPV-transformed epithelial cells, differently.

[Dendritic cells in dogs and cats: models of study in human pathology]

Langerhans' cells (LC) are epidermal bone-marrow-derived dendritic cells. They represent in mankind 1 to 6% of the epidermal cells from which they can be distinguished by specific phenotype (membrane receptors and antigens related to the immune function) and by ultrastructural specific organelles: the Birbeck granules. In dogs and cats, such cells were recently described; they display a phenotype very similar to that of human LC (CD1, CD8, CD11/18, CD45 and MHC II positive for canine LC, and CD18, CD4, panleukocyte antigen and MHC II positive for feline ones) and in both species, Birbeck granules are observed. Furthermore occurs in dog a benign self-healing LC tumor: the canine cutaneous histiocytoma (CCH). This tumor exhibits numerous comparison points with a human LC disorder named Hashimoto-Pritzker disease, and thus may constitute an interesting model to explore causes of such a proliferation and mechanisms of tumor rejection. In 1986, Pedersen isolated in cats a new retrovirus very similar to the human immunodeficiency virus (HIV), the feline immunodeficiency virus (FIV). Since human LC may be infected by HIV, feline LC may represent a good candidate for an FIV model for exploring the infection of human LC by the HIV and for shedding light on the role of human LC located in the mucous membranes in the initial viral inoculation process.

Human dendritic Langerhans cells generated in vitro from CD34+ progenitors can prime naive CD4+ T cells and process soluble antigen

Earlier studies have concluded that fresh Langerhans cells (LC) are able to capture and process native Ags, whereas cultured LC have lost these functions while acquiring the capacity to prime naive T cells. Herein we studied the functions of human dendritic/Langerhans cells (d-Lc) generated in vitro by culturing CD34+ hemopoietic progenitor cells in the presence of granulocyte-macrophage CSF (GM-CSF) + TNF-alpha. Less than 50 d-Lc were found to strongly stimulate the proliferation of 2.5 x 10(4) allogeneic naive CD4+ T cells. Furthermore, six to 50 d-Lc induced half-maximal proliferation of naive syngeneic CD4+ cord blood T cells, in the presence of picomolar concentrations of superantigens. During the alloreaction, the CD4+ T cells were expanded up to 100-fold within two successive stimulation cycles with the same d-Lc, and the recovered T cells were specific for the d-Lc alloantigen. HLA-matched tetanus toxoid (TT)-specific T cell clones were found to proliferate in response to TT presented by CD1a+ d-Lc. Finally, electron microscopy demonstrated that CD1a+ d-Lc were able to capture an Ag (gold-labeled Igs) through receptor-mediated endocytosis. Thus, in vitro generated d-Lc can prime naive T cells and process native Ags, a property that might eventually prove useful for priming Ag-specific naive T cells for cellular immunotherapy.

[Epithelial dendritic cells and HIV-1 infection in vivo and in vitro]

The skin and mucosa are the first line of defense of the organism against external agents, not only as a barrier between the body and the environment but also as the site of initiation of immune reactions. The immunocompetent epidermal cells which act as antigen-presenting cells (APC) are Langerhans cells (LC). Many indirect and/or direct experimental data have shown that LC may be a privileged target, reservoir and vector of dissemination for the human immunodeficiency virus (HIV) from the inoculation sites (mucosa?) to lymph nodes where the emigrated infected LC could infect T lymphocytes. In vitro infection confirms their permissivity to viral replication. HIV infection may modify the APC function of LC which could contribute to amplify the immunosuppressive state found in AIDS. Furthermore, mechanisms leading to the re-activation of viral expression at the cutaneous level need to be explored. An ideal animal model may readily clarify the role of LC in AIDS pathology and in transmucosal infection.

Human dendritic Langerhans cells generated in vitro from CD34+ progenitors can prime naive CD4+ T cells and process soluble antigen

Earlier studies have concluded that fresh Langerhans cells (LC) are able to capture and process native Ags, whereas cultured LC have lost these functions while acquiring the capacity to prime naive T cells. Herein we studied the functions of human dendritic/Langerhans cells (d-Lc) generated in vitro by culturing CD34+ hemopoietic progenitor cells in the presence of granulocyte-macrophage CSF (GM-CSF) + TNF-alpha. Less than 50 d-Lc were found to strongly stimulate the proliferation of 2.5 x 10(4) allogeneic naive CD4+ T cells. Furthermore, six to 50 d-Lc induced half-maximal proliferation of naive syngeneic CD4+ cord blood T cells, in the presence of picomolar concentrations of superantigens. During the alloreaction, the CD4+ T cells were expanded up to 100-fold within two successive stimulation cycles with the same d-Lc, and the recovered T cells were specific for the d-Lc alloantigen. HLA-matched tetanus toxoid (TT)-specific T cell clones were found to proliferate in response to TT presented by CD1a+ d-Lc. Finally, electron microscopy demonstrated that CD1a+ d-Lc were able to capture an Ag (gold-labeled Igs) through receptor-mediated endocytosis. Thus, in vitro generated d-Lc can prime naive T cells and process native Ags, a property that might eventually prove useful for priming Ag-specific naive T cells for cellular immunotherapy.

Functional expression of CD40 antigen on human epidermal Langerhans cells

It is now well established that interactions of CD40 on the B cells, along with its ligand (CD40-L) on the T cells, regulate B cell proliferation and differentiation. However, the functional significance of CD40 expression on cells known for most efficient Ag-presenting function, i.e., dendritic cells, is not so clear. In this study, we demonstrate that CD40 is expressed on human dendritic Langerhans cells (LC) freshly isolated from epidermis. Using CD40-L transfected cells, CD40 triggering was found to enhance LC viability when cultured and to result in phenotypic alterations. Thus, a 2-day CD40 activation induced up-regulation of CD54 and CD86 at the LC surface, while it did not significantly affect the levels of HLA-DR, CD1a, CD58, and CD80 expression. These phenotypic changes correlate with enhanced LC allostimulatory property, as shown by the use of paraformaldehyde-fixed LC. Furthermore, mAbs against CD40, as well as CD40-L, strongly inhibit the primary T cell response to allogeneic LC. Collectively, these data support a role for CD40/CD40-L pair in the development of normal T cell functions.

Functional expression of CD40 antigen on human epidermal Langerhans cells

It is now well established that interactions of CD40 on the B cells, along with its ligand (CD40-L) on the T cells, regulate B cell proliferation and differentiation. However, the functional significance of CD40 expression on cells known for most efficient Ag-presenting function, i.e., dendritic cells, is not so clear. In this study, we demonstrate that CD40 is expressed on human dendritic Langerhans cells (LC) freshly isolated from epidermis. Using CD40-L transfected cells, CD40 triggering was found to enhance LC viability when cultured and to result in phenotypic alterations. Thus, a 2-day CD40 activation induced up-regulation of CD54 and CD86 at the LC surface, while it did not significantly affect the levels of HLA-DR, CD1a, CD58, and CD80 expression. These phenotypic changes correlate with enhanced LC allostimulatory property, as shown by the use of paraformaldehyde-fixed LC. Furthermore, mAbs against CD40, as well as CD40-L, strongly inhibit the primary T cell response to allogeneic LC. Collectively, these data support a role for CD40/CD40-L pair in the development of normal T cell functions.

cis-urocanic acid failed to affect in vitro human Langerhans cell allostimulatory function

Urocanic acid (UCA) represents the major ultraviolet B (UVB, 290-320 nm)-absorbing component of the skin. Trans-UCA is naturally produced in the stratum corneum and converts to the cis isomer upon UVB irradiation. In this study, we examined the effect of purified cis-UCA (about 99% of cis isomer) on the human Langerhans cell (LC) allostimulatory function by using the mixed epidermal cell-lymphocyte reaction (MELR). We found that addition of increasing amounts (6.5-400 micrograms/mL) of purified cis-UCA or trans-UCA did not modify the T-cell response supported by enriched LC (eLC: 8-25% LC) as well as purified LC (pLC: 70-90% LC) suspensions. Because cis-UCA had no effect on the allostimulatory function of untreated LC, we investigated whether this compound could modify T-cell proliferation induced by UVB-irradiated LC. The UVB exposure of eLC or pLC to 100 J/m2 significantly inhibited the capacity of both suspensions to mount a T-cell response. However, addition of cis-UCA did not potentiate this UVB-induced immunosuppression. The eLC or pLC were then incubated with cis-UCA for 18 h at 37 degrees C and washed before adding to allogeneic T cells. The obtained proliferative response was similar to that induced by control LC incubated in medium alone, demonstrating that pretreatment with cis-UCA did not alter human LC function. In conclusion, these results strongly suggest that cis-UCA has no direct effect on human LC antigen-presenting function.

Monoclonal antibodies to human epidermal filaggrin, some not recognizing profilaggrin

To improve understanding of human profilaggrin processing to filaggrin, we produced seven monoclonal antibodies against epidermal filaggrin (AHF1-7). They were characterized on human epidermis by indirect immunofluorescence, immunogold labeling, and immunoblotting and found to be directed against seven different epitopes of (pro)filaggrin. AHF1-5 labeled the keratohyalin granules and the fibrous matrix of the lower corneocytes, and recognized filaggrin and profilaggrin. AHF6 also labeled the keratohyalin granules and the corneocyte matrix, but only recognized filaggrin. In addition to this reactivity within the upper epidermis, AHF4-6 stained the cytoplasm of the basal cells, and cross-reactivity of AHF5 and AHF6 with cytokeratin K14 was revealed on immunoblots. It is interesting that AHF7 recognized filaggrin, but not profilaggrin, and labeled only the corneocyte matrix and not the keratohyalin granules. This indicates that filaggrin and cytokeratins share several antigenic determinants and that filaggrin bears at least one epitope absent from its precursor. The original series of monoclonal antibodies described here appears to be a powerful tool for studying human profilaggrin processing in normal conditions and in the keratinization disorders in which processing is altered.

Expression of ICAM-3/CD50 in normal and diseased skin

ICAM-3 is a newly recognized adhesion molecule, which is a member of the immunoglobulin supergene family of ICAMs, and has been shown to be identical with the CD50 antigen. Recent functional studies have shown that ICAM-3 is a ligand for LFA-1, and plays an important part in immune reactions. To date, very few data exist in the literature concerning its expression in the skin. In the present study, we investigated the expression of ICAM-3 in normal skin and in 98 biopsy specimens of various inflammatory and neoplastic dermatoses. ICAM-3 was found to be expressed by epidermal CD1a+ Langerhans cells, by cells of Langerhans cell histiocytosis, by T and B lymphocytes infiltrating the dermis in cutaneous lymphomas and in a wide spectrum of inflammatory dermatoses. Epidermal keratinocytes were consistently negative; endothelial expression of ICAM-3 was observed in six of the 98 cases. These results show that ICAM-3 is constitutively and widely expressed by cells participating in inflammatory dermatoses (including Langerhans cells and T and B lymphocytes), and that it can be, albeit rarely, induced on endothelial cells and dermal dendrocytes. These results highlight the important part that ICAM-3 may play in cutaneous inflammatory and immune reactions.

Ultrastructural localization of binding sites of sera from patients with linear IgA bullous dermatosis

The localization of the antigen recognized by IgA basement membrane zone (BMZ) antibodies from patients with linear IgA bullous dermatosis (LABD) has not been established. The aim of our study was to find out the binding sites for IgA-BMZ antibodies in LABD in adults and children and, for comparison, the binding sites for IgA antibodies in IgA cicatricial pemphigoid (IgA-CP). Our series comprised 21 sera from adult LABD, 4 sera from childhood LABD, and 2 sera from IgA-CP. The studies were performed using the sodium chloride split-skin method and indirect immunoelectron microscopy (IEM) with the use of the pre-embedding immunoperoxidase technique on two substrates: monkey oesophagus and normal human skin. Of the 27 sera, 24 reacted with the epidermis (19 from adult, 4 from childhood LABD and 1 from IgA-CP) and at the electron microscopic level labelled the upper part of the lamina lucida (LL) and/or hemidesmosomes, and 2 reacted with the dermis (1 from typical adult LABD and 1 from IgA-CP) and labelled the sublamina densa (SLD) region. Two sera were negative in IEM. In conclusion, the study indicated that the localization of the antigens is similar in adult and childhood LABD, and in IgA-CP.

In vitro effects of ultraviolet B radiation on human Langerhans cell antigen-presenting function

The effects of ultraviolet B radiation (UBV) on the immune function of human epidermal Langerhans cells (LC) were studied by using the mixed epidermal cell-lymphocyte reaction (MELR). Exposure of both enriched LC suspensions (eLC, 8-20% LC) and purified LC suspensions (pLC, 70-90% LC) to increasing doses of UVB radiation (25 to 200 J/m2) decreased the proliferative T cell response in a very similar dose-dependent way, suggesting that keratinocytes did not play a major role in the UVB-induced inhibition of MELR. Supernatants from irradiated cultured eLC or pLC failed to inhibit T cell proliferation induced by untreated pLC. Furthermore, addition of irradiated eLC to untreated pLC did not affec the allogeneic T cell response. Taken together, these results provide evidence that in vitro UVB-induced immunosuppression was not mediated by inhibitory soluble factors that could affect either LC allostimulatory property or T cell proliferative response. UVB irradiation of human LC inhibited the capacity of these cells to induce CD4+ as well as CD8+ T cell proliferation. UVB-irradiated LC also induced a decreased T cell response to recall antigen or mitogen. Moreover, addition of exogeneous cytokines such as IL-1 beta, IL-1 alpha, or IL-2 did not reverse the defective function of UVB-irradiated LC in MELR. The inhibitory effect of UVB radiation on human LC was not related to a decreased HLA-DR expression. Because cultured LC appeared to be less sensitive than freshly isolated LC to UVB-induced suppressive effects, the deleterious effects of UVB radiation on human LC allostimulatory properties may be associated with an impaired development of LC accessory function.

In vitro T cell response to staphylococcal enterotoxin B superantigen in chronic plaque type psoriasis

Recent studies have demonstrated the important role of CD4+ T cells in the pathophysiology of psoriasis. One of the current hypotheses is that triggering of the psoriatic inflammatory process could be secondary to CD4+ T cell activation by bacterial superantigens in the skin. In this study, IL-2-derived T cell lines were recovered from the blood and the skin of 4 patients with chronic plaque type psoriasis and of 2 patients with allergic contact dermatitis (ACD). Blood and skin T cell lines were tested for their ability to proliferate in vitro to staphylococcal enterotoxin B (SEB) presented by MHC class II expressing antigen-presenting cells. The results showed a significantly higher SEB-induced T cell proliferation in skin T cell lines as compared to blood T cell lines in 3 out of 4 psoriatic patients and in one of the 2 ACD patients. No difference between the skin and blood T cells for their response to phytohemagglutinin was observed. Furthermore the blood T cell lines from both patients and control individuals responded equally well to SEB. Thus psoriatic skin T cell lines were characterized by an enrichment in SEB-responding T cells. Since similar enhancement of SEB-responsive T cells was occasionally found in ACD patients, we propose that SEB could be an environmental factor associated with rather than responsible for psoriatic inflammation.

Role of specific successive contacts between extracellular matrix proteins and epidermal Langerhans cells in the control of their directed migration

To migrate from epidermis to regional lymph nodes, antigen-bearing epidermal Langerhans cells (LC) must move through extracellular matrix (ECM) of various composition. The present study was designed to contrast the ability of basement membrane (BM)- and dermis-ECM components to successively stimulate the adhesion of normal human epidermal LC, in vitro. For this purpose, we used highly enriched LC suspensions (70%-80%), allowed them to attach to one ECM substrate, and then studied the readhesion properties of these recovered ECM-attached LC to the same and different ECM substrates. Each of four ECM molecules (laminin (LM), fibronectin (FN), type I and type IV collagen) was tested in pairs. Readhesion of recovered LM and type IV collagen-attached cells did not affect readhesion to FN and type I collagen, indicating that the interaction of LC with the BM components can be normally followed by interaction with the dermis-ECM molecules. In contrast, readhesion of recovered FN-, type I collagen-, and type IV collagen-attached cells to LM was significantly reduced. The findings indicate that following contact to BM components, epidermal LC are able to attach to ECM proteins present in the dermis, whereas once they have made contact with ECM present in the dermis, they reduce their binding capacity to the BM laminin, suggesting the contact with the dermal components could prevent LC from reentering the epidermal compartment. Binding to LM and FN was also shown to induce a decline in the expression of CD1a, known as a specific marker restricted to epidermal LC.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of adhesion receptors in epidermal tumors: correlation with TNF alpha expressing cells

The expression of intercellular adhesion molecule-1 (ICAM-1), endothelial leukocyte adhesion molecule-1 (E-selectin) and vascular cell adhesion molecule-1 (VCAM-1) was investigated in a series of basal cell carcinomas and squamous cell carcinomas in comparison to benign viral-induced lesions (cutaneous warts, condyloma) and was correlated to the infiltration density and the presence of TNF alpha expressing cells. Tumor cells expressing ICAM-1 were frequently detected in squamous cell carcinoma and condyloma and were correlated with a dense infiltration of HLA-DR and LFA-1 positive cells. Tumor cells were devoid of ICAM-1 in other lesions. Tumor microvessels detected by Von Willebrand factor were consistently present but vessels expressing adhesion receptors were less frequent. E-selectin was usually intense and frequent, whereas VCAM-1 was rare except in dense infiltrated zones and in viral-induced lesions. In all samples, tumor cells strongly expressed TNF alpha. Though the cytotoxin has been reported to be an inducer of adhesion receptors, its expression in epidermal tumors did not correlate with a concomitant up-regulation of epithelial ICAM-1 or endothelial VCAM-1. This may contribute to a reduced influx of T cells into the tumors.

Major antigenic epitopes of bullous pemphigoid 230 kDa antigen map within the C-terminal end of the protein. Evidence using a 55 kDa recombinant protein

In order to obtain greater insight into the nature of B-cell epitopes in bullous pemphigoid (BP), we generated a BP recombinant protein of 55 kDa M(r) (rBP 55) from a cDNA sequence encoding for the carboxyterminal region of the 230 kDa BP antigen. Serum IgG from guinea-pigs immunized with rBP 55 stained the basement membrane zone of normal human skin and immunoprecipitated the rBP 55 protein, and also the 230 kDa BP antigen recovered from extracts of cultured keratinocytes, thus confirming that the rBP 55 amino acid sequence is present in native BP antigen. The reactivity of sera from 60 patients with BP was analysed using an immunoblot assay on epidermal protein extracts and on the rBP 55 protein. Forty of the 60 BP sera (66%) contained autoantibodies to the 230 kDa polypeptide in an epidermal extract, and 37 of these 40 sera (92%) recognized the rBP 55 protein. In contrast, no reactivity against rBP 55 was detected with 20 BP sera devoid of autoantibodies against the 230 kDa antigen. Likewise, sera from patients with autoimmune blistering skin disorders other than BP (epidermolysis bullosa acquisita or pemphigus vulgaris), and control sera, were unreactive to rBP 55. These results clearly demonstrate the immunogenicity and antigenicity of the C-terminal end of the 230 kDa BP antigen. They confirm that this 555 amino acid segment, corresponding to rBP 55, contains major epitopes which can bind BP patients' autoantibodies, and suggest that the rBP 55 protein could be useful for further characterization of these B-cell epitopes.

Expression of ICAM-3 on human epidermal dendritic cells

Three counter-receptors for LFA-1 of the immunoglobulin family have been discovered: ICAM-1, ICAM-2, and ICAM-3. Despite their homologies, their patterns of expression suggest specialized roles. The finding that ICAM-3 is much better expressed than other LFA-1 ligands on monocytes and resting T cells, and that this discovery may be important in the initiation of immune responses prompted us to search for the expression of ICAM-3 by human epidermal Langerhans cells (LC). Six out of eight different ICAM-3 monoclonal antibodies were found to be reactive with epidermal LC. Immunoelectron-microscopy staining revealed that 100% of freshly-isolated, typical Birbeck granules containing LC expressed ICAM-3. After one day and three days of culture, 100% of LC still expressed ICAM-3, but the staining intensity was decreased by 58% and 76% respectively. Immunoprecipitation of 125I surface-labeled LC with anti-ICAM-3 antibodies revealed a polypeptide with apparent M(r) of 122,000-125,000. To determine whether ICAM-3 was involved in LC function, mixed epidermal cell-lymphocyte reactions were performed with freshly isolated LC in the presence of various concentrations of different anti-ICAM-3 antibodies. Among the different antibodies tested, HP2/19 and CBR-IC3/1 were found to partially block the reaction in a dose-dependent manner, suggesting that ICAM-3 represents a new molecule involved in the initiation of the immune response driven by epidermal LC.

Altered expression of a new antigen of the dermal-epidermal junction (NU-T2 DEJ Ag) in junctional epidermolysis bullosa

NU-T2 antigen (Ag) is a new and recently described antigen of the dermal-epidermal junction, recognized by an anti-CD1b monoclonal antibody denominated NU-T2. We studied NU-T2 Ag expression in junctional epidermolysis bullosa (13 patients) and in other forms of hereditary epidermolysis bullosa (23 patients), comparing the results with nicein expression. In junctional epidermolysis bullosa gravis type no differences were found between the expression of NU-T2 and nicein, both being negative in bullous as well as in non-bullous skin. Interestingly, in mitis type junctional epidermolysis bullosa, NU-T2 Ag was found to be absent or reduced in five of six patients both in lesional and in uncleaved skin. When compared with nicein expression, clearcut differences were found, further suggesting that these two antigens are different. These data confirm that NU-T2 Ag is a novel epitope of the dermal-epidermal junction, probably relevant in dermal-epidermal cohesion, and it could be responsible, together with nicein, 19-DEJ-1 and other adhesion molecules, for the different subtypes of junctional epidermolysis bullosa. Finally, NU-T2 monoclonal antibody is a new relevant tool for the diagnosis, classification, and prenatal diagnosis of junctional epidermolysis bullosa.

Analytical methods for evaluation on whole cells of human papillomavirus infection

Analytical methods for evaluation on whole cells of human papillomavirus infection. Human papillomavirus (HPV) infection is currently identified by the presence of viral DNA using molecular biology. As in situ hybridization is valuable for HPV-DNA detection mainly with non-isotopic probes, we evaluated the sensitivity of various techniques, using as models three cell lines containing different copy numbers of HPV DNA/cell (CaSki with 600 copies of HPV 16, SiHa with 1-2 copies of HPV 16, HeLa with 10-50 copies of HPV 18). Epifluorescence microscopy and flow cytometry allowed detection of 600 copies in CaSki cells; in addition, cell fixation was found to influence the fluorescent intensity. Several procedures were assayed to increase the sensitivity of in situ hybridization. The use of biotinylated HPV-16 oligonucleotides as probes was not effective, because only CaSki cells were positive. After amplification of HPV-16 or -18 DNA sequences with polymerase chain reaction (PCR) on whole cells in suspension and hybridization with plasmid probes, fluorescent hybridization spots were found in CaSki and HeLa cells by both epifluorescence microscopy and flow cytometry. The various procedures applied for revelation of DNA-DNA hybrids (use of phycoerythrin or cyanine instead of fluorescein, Pinkel's 3-step amplified system of fluorescein) did not enhance the sensitivity of in situ hybridization. HPV DNA was very effectively detected by cell examination under a laser-scanning confocal microscope, since 1-2 copies of HPV 16 were observed in SiHa cells without previous PCR amplification. Thus, the efficacy of in situ hybridization for HPV detection may be conditioned by different factors. Laser-scanning microscopy represents an alternative to the use of PCR amplification. These techniques are potentially useful to study single genes.