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The goal of the First International Equine Gene Mapping Workshop, held in 1995, was the construction of a low density, male linkage map for the horse. For this purpose, the International Horse Reference Family Panel (IHRFP) was established, consisting of 12 paternal half-sib families with 448 half-sib offspring provided by 10 laboratories. Blood samples were collected and DNA extracted in each laboratory and sent to the Lexington laboratory (KY, USA) for dispatch in aliquots to 14 typing laboratories. In total, 161 markers (144 microsatellites, seven blood groups and 10 proteins) were tested for all families for which the sire was heterozygous. Genealogies and typing data were sent for analysis to the INRA laboratory (Jouy-en-Josas, France) according to a specific format and entered into a database with input verification and output processes. Linkage analysis was performed with the CRIMAP program. Significant linkage was detected for 124 loci, of which 95 were unambiguously ordered using a multipoint analysis with an average spacing of 14.2 CM. These loci were distributed among 29 linkage groups. A more comprehensive analysis including synteny group data and FISH data suggested that 26 autosomes out of 31 are covered. The complete map spans 936 CM.

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Freshly isolated, and established, cultures of bovine peripheral blood mononuclear leukocytes (PBMLs) were exposed to bluetongue virus (BTV) for the purpose of defining potential lymphotropism. PBML cultures were established in the presence of interleukin 2 (IL-2) and mitogen and maintained either as bulk culture or were cloned prior to infectivity studies. All cultures appeared to be of the T cell phenotype based on the following characteristics: binding of T lymphocyte-specific lectins (i.e. peanut agglutinin and Helix pomatia), rosetting of sheep erythrocytes, binding of a putative pan-T monoclonal antibody, and absence of surface immunoglobulin (Ig). T lymphocyte cultures were further characterized by their ability to elicit lectin-dependent cellular cytotoxicity (LDCC). Exposure of established lymphocyte cultures to BTV resulted in productive cytopathic and non-cytopathic infections. Non-cytopathic productive infections were observed in LDCC-negative cultures whereas cytopathic and non-cytopathic infections were observed in LDCC-positive cultures. Exposure of freshly isolated PBMLs to BTV resulted in minimal virus replication; addition of mitogen and IL-2 to such cultures did not augment virus replication. Addition of mitogen and IL-2 induced negligible blast transformation, whereas PBML viability was minimally affected. These studies establish a tropism of BTV for bovine T lymphocytes with virus replication being limited to those cells undergoing blastogenesis. Establishment of infected lymphocyte cultures, without loss of culture viability, suggest such an interaction may contribute to the long term viraemias associated with BTV infection of cattle.

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