Major histocompatibility complex antigens in normal, acanthotic and neoplastic ovine skin: an association been tumor invasiveness and low level MHC class I expression

‘Ovar-Mhc‘— Ovine major histocompatibility complex: Role in genetic resistance to diseases

Research on the structure of the ovine major histocompatibility complex (MHC), Ovar-Mhc, and its association with resistance to various diseases in sheep has received increasing attention during recent years. The term 'resistance' is used to denote the capacity of an animal to defend itself against disease or to withstand the effects of a harmful environmental agent. The Ovar-Mhc is poorly characterised when compared to MHCs of other domestic animals. However, its basic structure is similar to that of other animals, comprising Class I, II and III regions. Products of the Class I and II genes, the histocompatibility molecules, are of paramount importance as these present antigens to T-lymphocytes, thereby eliciting immune responses. Several studies have been conducted in sheep on the involvement of MHC genes/antigens in genetic resistance to diseases, the majority being concerned with gastrointestinal nematodes. Studies on resistance to footrot, Johne's disease and bovine leukaemia virus (BLV)-induced leukaemogenesis have also been reported. Genes of all three regions were implicated in the disease association studies. In addition to disease resistance, Ovar-Mhc genes have been found to be associated with traits such as marbling and birthweight. The use of genetic markers from within the Ovar-Mhc may be useful, via marker-assisted selection, for increasing resistance to various diseases provided they do not impact negatively on other economically-important traits. This review summarises current knowledge of the role of Ovar-Mhc in genetic resistance to diseases in sheep.

Alterations of epidermal proliferation and cytokeratin expression in skin biopsies from heavy draught horses with chronic pastern dermatitis

We report the historical, clinical and histopathological characteristics of skin lesions in biopsies from 37 heavy draught horses with chronic pastern dermatitis. The skin lesions were divided into four macroscopic groups: scaling (group I, n=5), hyperkeratotic and hyperplastic plaque-like lesions (group II, n=14), nodular skin masses (group III, n=16) and verrucous skin lesions (group IV, n=2). The principal histological findings were hyperkeratosis and epidermal hyperplasia. There was a gradual increase in epidermal hyperplasia from groups I to IV, suggesting that the lesions represent different stages of disease. In all cases, there was perivascular dermatitis dominated by T lymphocytes with an increase in MHC class II-positive dendritic-like cells. Immunohistochemical labelling for cytokeratins CK5/6(4), CK10 and CK14 indicated a change in their expression pattern. This correlated with the degree of epidermal hyperplasia, indicating abnormal differentiation of keratinocytes. There was a statistically significant correlation between the severity of skin lesions and several other factors including increasing age, increasing cannon circumference, prominence of anatomical structures such as fetlock tufts of hairs, ergots and chestnuts, and bulges in the fetlock region.

Distribution of MHC-II and CD1 molecules in the skin of lambs and changes during experimentally-induced contact hypersensitivity

The presentation of antigen to specific T-cell populations is a crucial event during the elicitation phase of contact hypersensitivity (CHS). Significant changes in CD4(+) T-cell and gammadelta T-cell populations occur in the skin of sheep 48h after re-exposure to dinitrochlorobenzene but the expression of antigen presentation molecules such as MHC-II and CD1 at this stage of the hypersensitivity response has not been investigated. In the present study, a panel of monoclonal antibodies recognising CD1 and MHC-II subtypes was used in combination with computer assisted morphometric analysis to estimate the distribution of antigen presentation molecules in the superficial and deep dermis of the ears of lambs during the elicitation phase of CHS. The MHC-II molecules showed predominantly a perivascular and peri-appendageal distribution in the dermis and there were scattered MHC-II(+) cells in the basal and suprabasal layers of the epidermis. The CD1w2(+) (CD1b-like) molecules were present on distinct cells that were scattered evenly through the dermis, whereas CD1w3(+) (CD1c-like) molecules were almost exclusively detected on or in close association with the vascular endothelium. There was a significant increase in the presence of MHC-DQ(+) cells in the superficial dermis of dinitrochlorobenzene-treated animals compared with both an untreated control group and a vehicle-treated control group. However, MHC-DQ/DR(+) and CD1w3(+) cells only showed a significant increase compared with the vehicle-treated control group. The present study shows that the distribution of molecules involved in antigen presentation to CD4(+) T-cells and gammadelta T-cells changes during the elicitation phase of CHS in sheep, and suggests a role for MHC-DQ molecules on antigen presenting cells. However, the changes in distribution and expression of MHC-II and CD1 subtypes argue against a prominent role for a CD1-dependent pathway for T-cell recognition in the clinical cutaneous hypersensitivity response in sheep. Based on the expression of MHC-II molecules and CD1c molecules, we also suggest a potential role for endothelial cells in antigen presentation during the clinical dermatitis reaction.

Immunohistochemical study of the inflammatory infiltrate associated with equine squamous cell carcinoma

The distribution of T (CD3), B (CD79) lymphocytes, immunoglobulin (IgG, IgM and IgA)-producing plasma cells, macrophages (lysozyme, Mac387) and MHC Class II antigen was analysed in the inflammatory infiltrate associated with 19 equine squamous cell carcinomas (SCCs) and six cases of precancerous lesions (actinic keratosis). The SCCs came from the penis (11 cases), conjunctiva (four), skin (two), nasal cavity (one) and oral cavity (one). Seven cases were well-differentiated and 12 moderately differentiated. Nine cases showed no invasion of peritumoral deep tissues (locally invasive), whereas the remaining 10 cases were highly invasive. An abundant inflammatory infiltrate was associated with the majority of the SCCs and with lesions of actinic keratosis. This infiltrate was composed mainly of CD3(+)T lymphocytes, CD79(+)B cells and numerous IgG(+)plasma cells; IgM- and IgA-producing plasma cells were scarce and variable, respectively. Macrophages were usually numerous. Macrophages, lymphocytes, intra-epithelial dendritic cells and fibroblasts expressed MHC Class II antigen. No significant correlation was found between the nature of the inflammatory infiltrate and the SCC histological grade or degree of invasion, suggesting that the local anti-tumour immune response failed to prevent tumour invasion or metastasis. MHC Class II was expressed by a variable number of neoplastic epithelial cells in four SCCs, all of which were only locally invasive. In addition, in areas where SCC cells expressed Class II antigen, numerous CD3(+)T lymphocytes were present and some of them were associated with degenerate tumour cells. These findings suggest that the expression of MHC Class II by neoplastic cells induces an improved local anti-tumour immune response.

Immunohistochemical study of the inflammatory infiltrate associated with feline cutaneous squamous cell carcinomas and precancerous lesions (actinic keratosis)

The distribution of T lymphocytes (CD3+), B lymphocytes (CD79+), immunoglobulin-containing plasma cells (IgG, IgM and IgA), macrophages (Mac387+) and MHC Class II antigen was analysed in the inflammatory infiltrate associated with cutaneous squamous cell carcinomas (SCC) from 23 cats. Peri-tumoural skin (12 cases) and precancerous lesions of actinic keratosis (nine cases) were also evaluated for the expression of MHC Class II. The results revealed that an abundant inflammatory infiltrate was associated with the majority of SCC. This infiltrate was composed mainly of CD3+ T lymphocytes, B cells (CD79+) and IgG-bearing plasma cells, and the intensity of infiltration increased with the degree of invasiveness of the tumour. The number of CD3+ T cells and CD79+ cells was significantly increased in well-differentiated SCC compared with moderately differentiated tumours, whereas the number of IgM+, IgA+ plasma cells and Mac387+ macrophages was low or moderate and did not change significantly with histologic grade or invasiveness. MHC Class II antigen was expressed by infiltrating lymphocytes and macrophages, and by fibroblasts. A variable number of neoplastic cells (10% to 80%) in 10 SCC, and keratinocytes of basal layers in seven of nine cases of actinic keratosis also expressed MHC Class II, whereas keratinocytes of normal skin were always negative for this antigen. These results suggest that CD3+ T lymphocytes, CD79+ B cells and IgG-bearing plasma cells may participate in down-regulation of tumour growth, since these cell types were particularly numerous in well-differentiated and mildly invasive SCC, as well as in actinic keratosis. The expression of MHC Class II by neoplastic cells could enhance this local anti-tumour immune response.

Langerhans cells in the development of skin cancer: a qualitative and quantitative comparison of cell markers in normal, acanthotic and neoplastic ovine skin

The distribution of Langerhans cells in normal, acanthotic and neoplastic ovine epithelium was examined using the enzyme marker Acetylcholinesterase (AchE) and monoclonal antibodies (MoAb) to CD1 (20.27) and MHC Class II (49.1 and 28.1) molecules. In normal skin, where Langerhans cells were regularly spaced within the basal layer, qualitative observations and direct pairwise testing showed that AChE was superior to the MoAb in detecting these cells. Significantly more (P < 0.01) dendritic cells were also detected with MoAb 49.1 than MoAb 20.27 or 28.1, suggesting differential expression of MHC Class II subsets and the presence of CD1- MHC Class II+ granule- dendritic cells in sheep analogous to indeterminate cells of man. In acanthotic skin, compared to normal skin, Langerhans cells were less numerous, irregular and more suprabasal in distribution and their morphology was occasionally swollen and indistinct. No difference was seen in the ability of AChE and MoAb in detecting Langerhans cells, however pairwise testing of markers did demonstrate that significantly more (P < 0.05) cells without dendritic processes were stained with MoAb 49.1 than with 20.27 or 28.1. In all squamous cell carcinomas examined dendritic cells that stained for AChE, CD1 or MHC Class II antigens were concentrated at the peripheral areas of neoplastic epithelium. Many dendritic cells were detected with MoAb to MHC Class II antigens, whereas CD1 and AChE positive dendritic cells were rare in tumor bearing tissue. The quantitative differences in the immunohistochemical staining of Langerhans cells between normal, acanthotic and neoplastic epithelium were consistent with ultrastructural studies. When compared with those of a newborn lamb, which had had very little exposure to antigens or ultraviolet radiation (UVR), the Langerhans cells of the aged sheep were deformed and contained far fewer Birbeck granules. The abnormalities were progressively more severe in acanthotic and neoplastic skin. These observed changes may have resulted from UVR induced damage and may be indicative of impaired function involved in the development of skin cancer.