Badiola, G. detect the majority of infected animals and, when applied inside a molecular epidemiological context, to permit quick phylogenetic classification of the infecting disease. Caprine arthritis-encephalitis disease (CAEV) of goats and maedi-visna disease (MVV) of sheep belong to the genus of the family (18, 22, 39). Strong evidence shows that cross-species transmission from sheep to goats and vice versa happens under field conditions (16, 24, 33). Consequently, these viruses are no longer considered to be species specific and are referred to as small-ruminant lentiviruses (SRLV). The majority of infected animals mount a strong immune response I2906 to these viruses but remain persistently infected. Only one-third of infected goats develop overt medical disease, and in sheep the percentage of animals with medical symptoms differs greatly between breeds, strongly suggesting that, in both varieties, genetic factors play a key role in determining the clinical end result of illness (11, 28, 29). In several countries, eradication programs have been initiated to control SRLV-induced diseases with the aim of Alas2 removing these viruses (23). The Swiss CAEV eradication system, initiated in I2906 1984, offers reduced the seroprevalence from 60 to 80% to less than 1% and eliminated I2906 clinical instances in the goat human population (14, 15). However, in the last phase of the eradication system, detection and removal I2906 of the remaining disease service providers look like very hard. The serological tools currently used (37, 38) are of limited use when applied to screen a human population with a low seroprevalence. In the absence of reliable tools to directly detect SRLV, consistent serological diagnoses depend on the expensive use of a combination of checks run in parallel (4). Major problems in SRLV serology are sluggish seroconversions and low titers of antibody to Gag in some animals. In this respect, the strong immunogenicity of the envelope glycoprotein (Env) and especially I2906 the quick seroconversion induced by this antigen in infected animals make it an ideal candidate for diagnostic applications (2, 19). Goats and sheep infected with SRLV develop high titers of antibodies to several conformational and linear epitopes of Env (10, 12). However, particularly in goats, these antibodies do not display consistent neutralizing activity (19). The humoral immune response is definitely directed against the surface (SU) and transmembrane (TM) subunits of Env. Antibodies reacting with linear immunodominant epitopes of TM have been associated with disease in infected goats (3, 13, 17). The linear B-cell epitopes of Env were mapped for the CAEV-CO strain (2, 3, 35) and consist of six epitopes in the TM region and at least five in the SU region. One of the SU epitopes mapped previously (SU5) appeared to be particularly promising concerning its use like a diagnostic tool. When a limited panel of sera was tested for reactivity to SU5, this epitope appeared to be immunodominant and an early target of the antibody response in infected animals. Additionally, the sera tested showed a partly type-specific reaction, suggesting a possible application of these SU5 peptides in SRLV serotyping, as explained for human being immunodeficiency disease (HIV) with peptides related to the highly variable V3 loop region of Env (1, 25). The principal objectives of the present study were to amplify by PCR and sequence the genomic region encoding the SU5 antigenic site of several Swiss field isolates, to synthesize peptides related to their deduced amino acid sequences, and to test the hypothesis that these peptides are immunodominant and may be used to develop a novel SRLV serological test. MATERIALS AND METHODS Cell isolation. (i) PBMC. Peripheral blood mononuclear cells (PBMC) were isolated from EDTA-anticoagulated blood (Vacuette K3E EDTA K3; Greiner Labortechnik, Kremsmnster, Austria) by.