At least two loci encode polymorphic class I MHC antigens in the horse

The effect of skin allografting on the equine endometrial cup reaction

This research tested the hypothesis that immunological sensitization of mares by skin allografting, followed by the establishment of pregnancy using semen from the skin-graft donor, would give rise to secondary immune responses to the developing horse conceptus, resulting in an earlier demise of the fetally derived endometrial cups. Maiden mares received skin allografts from a stallion homozygous for Major Histocompatibility Complex (MHC) antigens and/or equivalent autografts and were subsequently mated to the skin-graft donor stallion during the next two breeding seasons. Mares that had been immunologically primed to the foreign MHC class I antigens of the skin-graft donor stallion developed strong secondary antibody responses early in their first pregnancies, whereas autografted mares made weak primary antibody responses in their first pregnancies and strong secondary responses in their second pregnancies. In contrast, histological examination of the endometrial cups after surgical pregnancy termination at Day 60 of gestation revealed no discernible differences between allografted and autografted mares, and there were no significant differences in the concentrations and/or duration of secretion of the endometrial cup-specific hormone, equine chorionic gonadotrophin (eCG), between allografted and autografted mares, nor in either group between first and second pregnancies. The vigorous antibody response observed in the pregnant allografted mares supported the first part of our hypothesis, providing evidence of systemic immunological priming. However, there was a lack of an equivalent heightened cellular response to the endometrial cups. These findings provided strong evidence for an asymmetric immune response to the conceptus, characterized by strong humoral immunity and a dampened cellular response.

Production and evaluation of alloantibodies against sheep MHC Class I antigens

In this work more than 600 sera obtained from three different sources (parous ewes and directed immunizations with whole blood or leucocytes) were tested for cytotoxic antilymphocyte antibodies. A high incidence of cytotoxic antibodies in pregnancy-stimulated animals was confirmed. For the sake of comparison, a comprehensive review of other studies in sheep and other species was performed. There are several different reasons that could explain the differences found between these studies, among them the time of sampling and the cytotoxic assay procedures. Moreover, antibodies were also found in non-pregnant females which may imply that pregnancy is not the only stimulus for antibody production and environmental factors, such as molecular mimicry between infectious agents and lymphocyte antigens, could be the reason for their appearance. In the case of alloimmunizations with leucocytes or whole blood the results were very close to those obtained in goats. Taking into account the Strength Index, the immunization sera were of higher quality. Our results support the methodology of Nesse and Larsen since one injection of whole blood of the lamb is an easy procedure that produces alloantisera with a high value for major histocompatibility complex Class I antigens typing.

Equine infectious anaemia virus proteins with epitopes most frequently recognized by cytotoxic T lymphocytes from infected horses

Efficacious lentiviral vaccines designed to induce cytotoxic T lymphocytes (CTL) in outbred populations with a diverse repertoire of MHC class I molecules should contain or express multiple viral proteins. To determine the equine infectious anaemia virus (EIAV) proteins with epitopes most frequently recognized by CTL from seven horses infected for 0.5 to 7 years, retroviral vector-transduced target cells expressing viral proteins were used in CTL assays. Gag p15 was recognized by CTL from 100% of these infected horses. p26 was recognized by CTL from 86%, SU and the middle third of Pol protein were each recognized by 43%, TM by 29%, and S2 by 14%. Based on these results, it is likely that a construct expressing the 359 amino acids constituting p15 and p26 would contain epitopes capable of stimulating CTL in most horses.

Report of the Second Equine Leucocyte Antigen Workshop, Squaw valley, California, July 1995

The final assignment of antibody clusters for leucocyte antigens and immunoglobulins, as described in detail in Sections 3 and 4, is summarized in Table 4. Together with other mAbs developed outside of ELAW II (Table 9) this pool of reagents represent a powerful array of tools for the study of equine immunity. The Second Equine Leucocyte Antigen Workshop made considerable advances in pursuing the objectives of establishing the specificities of mAbs and achieving consensus on the nomenclature for equine leucocyte and immunoglobulin molecules. Of equal importance, several productive collaborations were fostered among the participating laboratories and observers. Overall, enormous advances have been made in the past decade since mAbs specific for equine leucocyte antigens and immunoglobulins were first reported. There remains enormous scope and need for further studies of equine leucocyte antigens and immunoglobulins, both for the purposes of comparative immunology and for the good of the horse. In the future novel techniques will be required to develop reagents for specific target antigens such as the orthologues of the CD25 or CD45 isoforms. In studies of equine immunoglobulins the functional role of the IgG isotypes must be better established, reagents for IgE must be developed, and cloning of the immunoglobulin heavy chain genes will be essential if the complexities of the IgG sub-isotypes are to be elucidated. The tasks still facing the currently small group of equine immunologists throughout the world remain formidable, and will only be tackled successfully in a spirit of collaboration.

The equine homologue of LFA-1 (CD11a/CD18): cellular distribution and differential determinants

The equine homologue of the leucocyte integrin LFA-1 (CD11a/CD18) has been characterized using a panel of four monoclonal antibodies (mAbs). The antibodies labelled almost all leukocytes, thymocytes and lymph node cells from normal horses, and immunoprecipitated two noncovalently associated polypeptides with molecular weights of 180 kDa and 100 kDa, respectively. The antigen recognized by one mAb could be precipitated by another in this cluster in a sequential immunoprecipitation assay. The mAbs, however, did not block the activities on lymphocyte function of one another. A mAb to the beta subunit of human LFA-1 cross-reacted with equine LFA-1, but an antibody to its alpha subunit did not, suggesting that the beta subunit of the leukocyte integrin may be more highly-conserved. Functionally, H20A and a human CD18 antibody (MHM23) inhibited phorbol ester-mediated homotypic lymphocyte aggregation, whereas mAb CZ3.2 induced rather than inhibited the homotypic cell aggregation. The formation of lymphocyte aggregates induced by CZ3.2 was not blocked by the inhibitory antibodies H20A or MHM23. CZ3.1 seemed to have little inducible or inhibitory effects on homotypic cell aggregation. The mAb CZ3.1 defined a unique LFA-1 determinant present on granulocytes, but absent on lymphocytes in members of an extended horse family, in contrast to the other antibodies which labelled both granulocytes and lymphocytes from these animals. In all other horses tested, no differences in reactivity of CZ3.1 and the other LFA-1 antibodies were observed when the antibodies were tested on lymphocytes or granulocytes. Our results indicate that common epitopes are shared' between human and equine LFA-1, and that the described panel of monoclonal antibodies identifies distinct determinants present on the equine LFA-1 molecule. The following monoclonal antibodies used in this study were given official workshop designations at the Second International Workshop on Equine Leukocyte Antigens (Lunn et al., 1998) CZ3.1 (Cor) = W45; CZ3.2 (Cor) = W77.

Anti-alpha chain monoclonal antibodies of equine MHC class-II antigens: applications to equine infectious anaemia

This paper describes the characteristics of a monoclonal antibody (mAb), 6B11C3, that recognises most equine monocytic cells, as well as B- and T-lymphocytes. The T CD4+ and T CD8+ of this latter population are also stained by the 6B11C3 mAb. On the basis of the distribution of membrane antigens on these cell populations, and of immunohistochemistry results, this mAb appears to be an anti-equine class-II major histocompatibility complex (MHC) antigen. In horses, the hyperexpression of the MHC class-II antigen on T cells is an indication of activated lymphocytes. A decrease in the percentage of lymphocytes stained by 6B11C3 was observed in horses with persistent equine infectious anaemia.

The equine endometrial cup reaction: a review

The function of eCG in equine pregnancy is far from clear but it has become evident that eCG has little or no FSH activity in the horse and is therefore probably not responsible for the secondary ovulations. eCG does have luteotrophic activity and it could play a role in the resurgence of the primary corpus luteum (1,7,44). Some evidence exists that the receptor population on the equine gonads is heterogenous in a way that makes it possible to distinguish eCG from eLH, resulting in different post-receptor effects (7). There is also evidence that eCG itself is heterogenous, both in glycosylation and in primary structure, not only between different individual animals but also within one animal during different stages of gestation. The differences could simply reflect the difference between stored and secreted hormone, but on the other hand the release of different eCG forms could be under endocrine control, allowing the mare to produce forms appropriate to specific biological needs (74). Thus some forms of eCG could play a role in immunological events taking place at the foeto-maternal interface. The role of cytotoxic antibodies in the equine pregnancy is not understood. The fact that they are not harmful to the pregnancy can be explained by the fact that their target, the paternal MHC molecules, are withdrawn from the endometrial cup tissue by the time the antibodies start appearing in the circulation. This unique way of regulation of MHC expression is also poorly understood.(ABSTRACT TRUNCATED AT 250 WORDS)

An equine B cell surface antigen defined by a monoclonal antibody

A surface antigen of equine B lymphocytes was identified using the Equine Leucocyte Antigen Workshop antibody WS 65. This marker was expressed on almost all equine B cells, but not on T cells, granulocytes or thymocytes. WS 65 strongly stained cells in the follicular areas of lymph nodes and cells in the splenic nodules when tested on frozen tissue sections by immunohistochemistry. Equine leukemic T cells were not labeled by WS 65, and neither were the cells from a horse with B cell leukemia, although these latter cells carried surface immunoglobulin. Immunoprecipitation of lymphocyte membrane molecules with the antibody produced a band at 85-90 kDa under reducing conditions. The equine B cell antigen defined by WS 65 appears to be different from surface immunoglobulin by its molecular characteristics and its lack of expression on malignant B cells.

Report of the First International Workshop on Equine Leucocyte Antigens, Cambridge, UK, July 1991

The First International Workshop on Equine Leucocyte Antigens was organized and convened for the purposes of identifying immunologically relevant cell surface molecules of equine leucocytes and establishing a system of nomenclature for those molecules. Participating members of the workshop represented the majority of laboratories world-wide engaged in the tasks of production and characterization of equine leucocyte and lymphocyte markers using monoclonal antibodies. The workshop confirmed the identification of several equine CD molecules described previously by individual laboratories, and in addition recognized antibodies identifying new CD molecules. The workshop also succeeded in fostering co-operation between laboratories around the world which study equine immunobiology. Equine CD molecules identified by the current battery of monoclonal antibodies include EqCD2, EqCD4, EqCD5, EqCD8, EqCD11a/18, EqCD13 and EqCD44. Other antibodies are markers for MHC class I and class II molecules, for B cells, granulocytes, macrophages, T cell subsets distinct from those defined by CD4 and CD8, and other sub-populations of horse leucocytes that do not have obvious counterparts in humans, rodents, or other species. Despite the progress made in the first workshop, there are still substantial gaps in the armory of reagents available to study equine leucocyte biology, and further definition of the structure, function, and genetics of the antigens identified by the workshop clusters (WC1, WC2 etc.) and other molecules of immunological importance will be a goal of future workshops. The study of equine immunobiology and resistance to disease also urgently requires the development of tools to study equine immunoglobulins and cytokines, and these needs will provide ample scope for future studies.

Studies on the frequency and associations of equine leucocyte antigens in sarcoid and summer dermatitis

The equine leucocyte antigen (ELA) types and the clinical diagnosis for equine sarcoid and summer dermatitis were evaluated in 2026 horses representing five breeds. Data were analysed in unrelated animals and in family material. In the case of equine sarcoid, a strong association was observed between the ELA class II DW13 antigen and its effect on Swiss (cP < 0.001), French (cP < 0.0001) and Irish (cP < 0.01) Warmblood horses. The class I antigen A3 occurred more frequently in sarcoid-affected French horses (cP < 0.001). These results confirm our earlier findings (Gerber et al. 1988). Among Freiberger horses, which lack the ELA DW13 and A3 specificities, a breed-specific class I antigen, ABe108, displayed an increased frequency (cP < 0.05) in the affected group. Among Arabian horses, a tendency for increased frequency of the A1 antigen was observed in the affected animals, but the number of affected horses is too small for statistical significance. The Mendelian segregation in diseased half-siblings by ELA DW13 heterozygous stallions showed a strong association (P < 0.0001) between the inherited DW13 antigen and susceptibility to the sarcoid effect. In the case of summer dermatitis, previously published data (Marti et al. 1992) have been extended. The ELA types in four multiple-case families, founded by the same stallion, were analysed for an association with the effect of sarcoid. Eight out of nine ELA-typed affected offspring inherited the paternal haplotype A15, DW23 in contrast to nonaffected offspring where three out of 12 displayed these antigens (P < 0.005).(ABSTRACT TRUNCATED AT 250 WORDS)

Paternal and maternal major histocompatibility complex class I antigens are expressed co-dominantly by equine trophoblast

Invasive equine trophoblast cells of the chorionic girdle express high levels of paternally inherited Major Histocompatibility Complex (MHC) class I antigens prior to migration into the endometrium to form the so-called endometrial cups. Three groups of experiments were performed to determine if maternally inherited MHC class I antigens are expressed on chorionic girdle cells. Results indicated that maternally and paternally inherited MHC class I antigens are co-dominantly expressed by cells of the invasive equine trophoblast, and therefore, that the expression of polymorphic equine MHC class I genes does not appear to be affected by genomic imprinting in this tissue. The demonstration that cells of the chorionic girdle were immunogenic supports the hypothesis that invasion of the maternal endometrium by chorionic girdle cells stimulates the production of anti-paternal alloantibodies normally observed in early horse pregnancy. The co-dominant expression of MHC class I antigens by invasive chorionic girdle cells has important implications for the mechanism of recognition of allogeneic fetal MHC class I antigens by the maternal immune system.

A comparative review of human and equine leucocyte differentiation antigens

Monoclonal antibody technology has allowed the recognition and study of numerous leucocyte antigens in man and laboratory animals for over a decade. Numerous advances in the understanding of immune responses and immunopathology have resulted. In recent years equine researchers have started to develop similar reagents, which now offer a powerful tool to investigators of equine immunology and disease.

Developmental regulation of class I major histocompatibility complex antigen expression by equine trophoblastic cells

Between days 36-38 of pregnancy equine trophoblastic cells of the chorionic girdle migrate and form endometrial cups. Just prior to invasion, the chorionic girdle cells express high levels of polymorphic, paternally inherited, major histocompatibility complex (MHC) class I antigens. Their descendents, the mature, invasive trophoblast cells of the endometrial cups, however, express low or undetectable levels of MHC class I antigens by day 44 of pregnancy. Experiments with MHC compatible pregnancies, the study of residual chorionic girdle cells that had failed to invade the endometrium and remained on the surface of a conceptus, and the study of chorionic girdle cells recovered on days 34-36 of pregnancy and then maintained in vitro for up to 24 days strongly suggest that the reduction of MHC class I antigen expression by mature invasive trophoblast cells of the endometrial cups is developmentally regulated. This phenomenon does not appear to be induced by a maternal antibody response or by other uterine factors acting after the chorionic girdle trophoblast cells invade the endometrium.

Differentiation of chronic lymphocytic leukemia in the horse. A report of two cases

Chronic lymphocytic leukemia (CLL) was diagnosed in two horses: an 18-year-old Quarter Horse gelding that was examined because of edema of the prepuce and ventral abdomen; and a 20-year-old mixed breed gelding that was referred because of lymphocytosis, ventral edema, and weight loss. The first horse had enlarged peripheral lymph nodes and cool nonpainful pitting edema of the ventral abdomen and prepuce. The second horse had enlarged peripheral lymph nodes, cool nonpainful pitting edema of the ventral thorax and cranial ventral abdomen, and a 3/5 holosystolic heart murmur. The diagnosis of CLL was based on increased blood lymphocyte counts and infiltration of marrow and other tissues by lymphocytes. In horse 1, the lymphocytosis persisted for 2 months between initial examination and death. The results of flow cytometric analysis on blood lymphocytes using anti-lymphocyte antibodies suggested that horse 1 had T-cell CLL, and horse 2 had B-cell CLL. In addition, the second horse had a monoclonal gammopathy (IgG), with light-chain proteinuria.