Cytochemical and Ultrastructural Studies of the Langerhans' Cells

Turnover and kinetics of epidermal Langerhans cells and their dendritic precursor cells in experimental contact dermatitis. A correlated ultrastructural-morphometric and immunohistochemical evaluation

The numerical density of epidermal Langerhans cells (LCs) in contact sensitivity and toxic contact dermatitis is still a matter of controversy, mainly due to changes in the phenotypic markers of this antigen-presenting cell during the skin reactions. Since the electron microscopic detection of Birbeck granules is the most reliable marker for the identification of normal and pathologically altered LCs, we performed an ultrastructural-morphometric time-course analysis to evaluate their epidermal turnover in the earskin of BALB/c mice after painting the ears with the hapten 2,4-dinitrofluorobenzene and the irritant croton oil. The counts revealed degeneration and depletion of epidermal LCs in both allergic and toxic dermatitis. In contrast, a slightly increased number of activated epidermal LCs was found during contact sensitization. All experimental procedures resulted in an enhanced immigration of so-called indeterminate dendritic cells which also became ultrastructurally activated and often showed Birbeck granule-like formations at their cell membrane. Immunohistochemistry with the monoclonal antibody 4F7, a new marker for dendritic precursor cells of LCs, demonstrated a significant increase in these accessory cells in the epidermis. Our results indicate that contact sensitivity and toxic skin reactions are characterized by complex but distinct changes in the turnover, kinetics and cellular properties of epidermal LCs and their dendritic precursor cells.

Immunophenotyping of the cellular infiltrate in the early elicitation phase of contact dermatitis in the skin of presensitized atopic individuals

Little is known about the composition of the cellular infiltrate in the early elicitation phase of contact allergy in atopic individuals. Therefore, we rechallenged ten presensitized disease-free atopic volunteers with their known contact allergen and performed biopsies at time 0 and after 6 and 24 h. Ten patients with acute exacerbated atopic dermatitis in the early stage were chosen as a control group. Skin biopsy specimens were processed for immunohistochemistry (APAAP) and evaluated by computer-assisted morphometry. CD4+ and CD45R0+ cells were found to be significantly increased after 6 (t6) and 24 h (t24), and this was accompanied by an enhanced TCR alpha/beta receptor expression at t6-CD45O+ cells showed a marked influx into the epidermis at t24. CD8+ cells infiltrated the basal layer of the epidermis, thus changing the CD4/CD8 ratio from 4.6:1 at t0 to 2.2:1 at t6. CD1a+ epidermal dendritic cells increased significantly from 811 +/- 240/mm2 at t0, to 1210 +/- 333/mm2 at t24 (P < 0.01). At t6 and t24, a so-called 'epitope CD1a+ shedding' was observed into the intercellular spaces of keratinocytes as well as an elongation and enlargement of the dendrites of CD1a+ cells. In the upper dermis, the number of CD1a+ cells increased from 1098 +/- 485/mm2 at t0 to 2388 +/- 740/mm2 at t24 (P < 0.01). In 7/10 volunteers, IgE+ dendritic cells increased significantly in number at t6 (P < 0.02). The activation markers HLA-DR and CD25 were expressed most distinctly at t24. Interestingly, expression of ICAM-1 on keratinocytes occurred only in four of the ten atopic volunteers.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic nature and function of epidermal Langerhans cells in vivo and in vitro: a review, with emphasis on human Langerhans cells

Epidermal Langerhans cells (LC) are Birbeck granule-containing bone-marrow-derived cells, which are located mainly in the suprabasal layer of the epidermis. They can be readily identified by their strong expression of CD1a and MHC class II molecules. In addition to these 'classical' properties, an extensive phenotypic profile of normal human LC, summarized in this review, is now available. The powerful capacity of LC to activate T lymphocytes is clearly documented and, to date, LC are recognized as the prominent antigen-presenting cells of the skin immune system. They are generally believed to pick up antigens encountered in the epidermis and to migrate subsequently from the epidermis to the skin-draining lymph nodes. Upon arrival in the paracortex of lymph nodes, the antigen-laden LC transform into interdigitating cells and they present antigen to naive T lymphocytes in a MHC class II-restricted fashion; this results in the generation of antigen-specific immune responses. It has also been demonstrated that transformation of LC into interdigitating cells occurs when LC are cultured in vitro. Both in vivo and in vitro studies have indicated that properties of LC, such as phenotype, morphology and the stimulatory potential to activate T lymphocytes, are dependent on the local microenvironment in which the LC reside. The essential role of LC in the induction of contact allergic skin reactions and skin transplant rejection is well established.

Differential effects of structurally unrelated chemical irritants on the density and morphology of epidermal CD1+ cells

In order to gain a greater insight into the complex mechanisms of action of different irritant chemicals on the skin, we have studied the behavior of epidermal CD1+ cells in experimentally induced irritant contact dermatitis. Healthy, human volunteers were patch tested for 48 h with the following six chemically unrelated irritants and their appropriate vehicle controls; benzalkonium chloride, sodium lauryl sulphate, dithranol, nonanoic acid, croton oil, and propylene glycol. After visually assessing and grading the resulting inflammatory reactions, punch biopsies were taken and the morphology and density of CD1+ cells in the epidermis studied using immunocytochemical techniques in combination with image analysis and electron microscopy. Statistically significant decreases in the epidermal density of CD1+ cells occurred in the responses to dithranol (p less than 0.05) and nonanoic acid (p less than 0.01). Importantly, these changes in density were not simply due to variations in the intensity of inflammatory response (r = 0.1157). Alterations in the length of the dendritic processes of CD1+ cells were also induced, and semi-quantitative analysis revealed significant decreases in dendrite length in the reactions to sodium lauryl sulphate (p less than 0.05), nonanoic acid (p less than 0.001), croton oil (p less than 0.05), and dithranol (p less than 0.005). Unlike epidermal density, however, this effect on cell morphology was directly related to the severity of inflammation (r = -0.74, p less than 0.01). Morphologic evidence of cellular injury to Langerhans cells was seen by electron microscopy in the majority of biopsies, although relatively few cells were affected in sodium lauryl sulphate and propylene glycol reactions. Benzalkonium chloride, unlike the other irritants, also induced a state of metabolic activation in a high proportion of epidermal Langerhans cells. Lymphocyte/Langerhans cell apposition was observed in most samples, but was particularly prevalent in the reactions to dithranol. The results of this study demonstrate that significant changes in the morphology and density of Langerhans cells occur in irritant contact dermatitis, some of which are directly influenced by the chemical nature of the irritant.

Langerhans cells in human allergic contact dermatitis contain varying numbers of Birbeck granules. Double staining immunohistochemistry with OKT6 and Lag antibody

Dynamic changes in human Langerhans cells (LCs) were studied with OKT6, anti-HLA-DR antibody, and Lag antibody in allergic contact dermatitis (ACD). Both T6-positive (T6+) cells and Lag-positive (Lag+) cells in the epidermis decreased in number from 0 to 48 h, but then gradually increased after day 7 of ACD. Lag+ cells after day 7 manifested a variety of staining intensities from weak to strong. It was also shown, after day 7, that some T6+ cells were Lag negative whereas all Lag+ cells were T6 positive. Flow cytometric analysis suggested that Lag-strongly-positive cells and Lag-weakly-positive cells belonged to the same population, and that the relative amount of Lag antigens in T6+ LCs gradually increased after day 7. Immunoelectron microscopy revealed that the Lag-strongly-positive cells contained numerous Lag-reactive Birbeck granules (BGs) whereas the Lag-weakly-positive cells contained fewer BGs in the cytoplasm. In some Lag-weakly-positive cells, no BGs were detected.

Decreased number and function of antigen-presenting cells in the skin following application of irritant agents: relevance for skin cancer?

The mechanism of irritant dermatitis and the immunologic consequences of such reactions are unclear. We evaluated the number and function of epidermal antigen-presenting cells contained in epidermal cell suspensions obtained from normal and irritant patch test reaction sites. Application of sodium lauryl sulfate or croton oil to human skin in vivo resulted in a progressive depletion in the number of epidermal OKT6+HLA-DR+ (T6+DR+) Langerhans cells (LC) from 3.1 +/- 0.2% of total epidermal cells (EC) to 1.2 +/- 0.1% after 8 d (mean values +/- SEM, N = 9). Between 1-4 d irritant patch test sites demonstrated an influx of non-Langerhans cell T6-DR+ cells. These cells were not DR+ keratinocytes but appeared to be of bone marrow derivation because they expressed the marker, HLe1. Among bone marrow derived cells, the T6-DR+EC appeared to be of monocyte, macrophage lineage, because they expressed the determinant recognized by the OKM5 (M5) antibody. Despite the induction of M5+DR+EC the total number of DR+EC showed progressively decreasing percentages over an 8-d period. Partial recovery to 73 +/- 12% of control value was observed at 2 weeks, with full recovery by 4 weeks after challenge. Concomitantly with the depletion of DR+EC, the capacity of EC to present alloantigens to T cells decreased. This reduction in antigen-presenting cell activity was strongly correlated to the reduction in total DR+ EC (r = 0.94, p less than 0.05). Thus, the capacity of irritants such as croton oil to abrogate the function of epidermal antigen-presenting cells may be related to the tumor promoting potential of these agents.

Cellular kinetics of delayed hypersensitivity test reactions to topical glucocorticosteroids

The phenotypes of the infiltrating cells in 13 patients with delayed hypersensitivity to topical glucocorticosteroids (GCS) were studied from sequential biopsies of positive epicutaneous test reactions by using the avidin-biotin-complex (ABC) technique. Monoclonal antibodies were used to identify the cells with the following phenotypes: T3, T4/T4a, T6, T8, T9, T11, M1, Ia1 (HLA-DR), interleukin-2 receptor/T26a, and dendritic reticular cell. The cellular kinetics of GCS hypersensitivity reactions were compared with delayed hypersensitivity reactions caused by allergens not related to GCS. In both GCS and non-GCS reactions the epidermal dendritic T6+ cells were more numerous than dendritic Ia1+ cells. There was a decrease in the number of both cell types during these reactions; in GCS reactions the decrease in the number of T6+ cells was seen later than in non-GCS reactions. Ia1+ keratinocytes were seen at sites near dermal infiltrates. Compared with the non-GCS delayed hypersensitivity reaction, there were fewer pan T (T11+/T3+) in the GCS reaction. The relative numbers of M1+ monocytes and the T4/T8 ratio were substantially lower in the latter; these findings can be explained as a GCS effect which modulates the delayed type hypersensitivity reaction.

Ultrastructural and phenotypic changes in Langerhans cells induced in vitro by contact allergens

Ultrastructural changes of murine Langerhans cells (LC) were examined following exposure of crude epidermal cell suspensions to the contact allergens dinitrochlorobenzene, nickel sulphate and lead nitrate at various concentrations and for various incubation times. An immunogold labelling technique was employed to study changes in surface expression of MHC Class II (Ia) molecules. In all cases, activation of LC was evident after as little as 15 min exposure and was characterized by a marked increase in surface expression of Ia molecules, prominent rough endoplasmic reticulum and numerous ribosomes and lysosomes. Degenerative changes in LC were apparent to varying degrees depending on the allergen, its concentration and the time of incubation. Degenerative changes included swollen mitochondria, membrane disruption or rupture, loss of density of the cytoplasm (cytolysis), loss of dendritic processes and decreased expression of Ia molecules. In the case of dinitrochlorobenzene, degenerative changes were present and usually severe at concentrations greater than 10 micrograms/ml, while exposure to nickel sulphate and lead nitrate was associated with only mild degenerative changes. These observations indicate that contact allergens have a variety of direct effects on LC, including activation and degeneration, which are dose- and time-dependent. Since these alterations of LC were observed in the absence of other immunologically active cells, peripolesis cannot be involved in these events.