Summary Peripheral blood lymphocytes (PBL) of T. evansi‐infected or uninfected ponies were cultured in vitro with different concentrations of T. evansi, a soluble fraction, or isolated variable surface glycoprotein (VSG). It was found that only the soluble fraction could induce the proliferation of the PBL in vitro. This antigen preparation had a mitogenic effect because it could stimulate cells from uninfected animals. Optimal stimulation of PBL was only recorded after application of large amounts of the soluble fraction and 5–6 days incubation. PBL of T. evansi‐infected ponies, however, could not be stimulated by any of the three preparations. Zusammenfassung In vitro‐Stimulation peripherer Blutlymphozyten des Ponys durch eine lösliche Fraktion von Trypanosoma evansi Periphere Blutlymphozyten von Trypanosoma evansi‐infizierten und nicht infizierten Ponys wurden in vitro mit verschiedenen Konzentrationen von lebenden T. evansi, einer löslichen Parasiten‐fraktion, oder isoliertem Oberflächenantigen (VSG) der Erreger kultiviert. Dabei zeigte es sich, daß nur die lösliche Fraktion in der Lage war, die Lymphozyten zu einer in vitro‐Proliferation anzuregen. Da nur Lymphozyten von nicht infizierten Tieren in vitro stimuliert werden konnten, ist anzunehmen, daß diese Antigenpräparation eine mitogene Wirkung hat. Eine optimale Stimulation der Zellen fand jedoch erst nach Verwendung höherer Konzentrationen des Antigens und nach einer Inkubationszeit von fünf bis sechs Tagen statt.

Groups of eight miniature pigs were infected either with 1,500 embryonated eggs each of Ascaris suum or Toxocara canis or with 1,000 eggs each of both nematodes. Sera were sampled before the infection as well as three and six weeks postinfection and then investigated in the ELISA on microtitre plates against antigens of various developmental stages. When extracts of adult Ascaris and Toxocara worms were used as antigens, distinct reactions were registered both in the infected and in the uninfected control groups. Antigens isolated from either embryonated eggs or larvae of both worms produced distinctly positive reactions with sera of the infected animals, including those pigs with heterologous infections but not with sera from uninfected controls. After saturation with heterologous antigens, the sera showed distinct antibody reactions against homologous antigen extracts and in this way infections with the two nematode species could be serologically differentiated.

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Summary Pony peripheral blood lymphocytes (PBL) were stimulated with a soluble fraction of Trypanosoma (T.) evansi (SF). As determined by 3H‐thymidine incorporation, the cells underwent a proliferative response and were able to: a) produce a factor having the biological activities of interleukin 2 (IL‐2) since their supernatants could support the in vitro growth of pony PBL stimulated with concanavalin A (Con A‐blasts); b) undergo a further proliferative response when incubated in short term cultures with SF, human recombinant IL‐2 (hrIL‐2), or both c) bind specifically radiolabelled hrIL‐2 (125I‐hrIL‐2). The date described here indicate that a soluble fraction of T. evansi stimulated pony PBL which subsequently produced IL‐2 and expressed IL‐2 receptors (IL‐2R).

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