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The purpose of this study was to monitor abundance and activation of local CD8β-expressing T-cell populations during Eimeria tenella infections of naïve chickens and chickens immune by previous infections. Chickens were infected with E. tenella up to three times. Caecal T-cell receptor (TCR) γ/δ-CD8β+ cells (cytotoxic T lymphocytes; CTL) and TCRγ/δ+CD8β+ cells were characterized with respect to activation markers (blast transformation, CD25 and cell surface CD107a). Cells were also induced to degranulate in vitro as a measure of activation potential. Major findings included a prominent long-lasting, up to 6 weeks, increase in the proportion of CTL among caecal CD45+ cells in the later stages after primary E. tenella infection. These CTL also showed clear signs of activation, that is blast transformation and increased in vitro induced degranulation. At second and third E. tenella infection, chickens showed strong protective immunity but discrete signs of cellular activation were observed, for example increased in vitro induced degranulation of CTL. Thus, primary E. tenella infection induced clear recruitment and activation of local CTL. Upon subsequent infections of strongly immune chickens cellular changes were less prominent, possibly due to lower overall numbers of cells being activated because of the severe restriction of parasite replication.

The effect of Leishmania tropica major excreted factor (EF) on human immune and normal mononuclear peripheral blood cells has been studied. The response of lymphocytes to stimulation either specifically with leishmanial antigens or non-specifically with phytohemagglutinin (PHA) in the presence of EF was tested by the uptake of 3 [H]thymidine. The results showed that EF inhibits the response of cells from immune donors to leishmanial antigens and from normal donors to PHA or PPD. Adherent and non-adherent cells were separated and the effect of EF on both populations was analysed. The results showed that EF inhibited blast transformation if both EF and antigen were presented to each of the separate populations. The inhibition of the adherent cells (mainly monocytes) was more marked than the inhibition of the non-adherent population (mainly lymphocytes).