Kinetics of IL-2 receptor expression on lymphocyte subsets from goats infected with Mycobacterium avium subsp. paratuberculosis after specific in vitro stimulation

Quantification of surface IL-2R expression on activated lymphocytes by flow cytometry have recently been reported to be useful in measuring cellular immunity against Mycobacterium avium subsp. paratuberculosis in goats (Whist et al., 2000, Vet. Immunol. Immunopathol. 73, 207–218). To characterise the phenotype of the peripheral lymphocytes expressing IL-2R after in vitro stimulation with purified protein derivate (PPD) from M. a. paratuberculosis, cells were processed for dual or triple colour analysis by flow cytometry (CD4 and IL-2R or CD8, γδ-TcR and IL-2R). To distinguish the response of antigen-specific T cells from non-specific stimulation, we performed a time-course study of proliferating cells in a group of M. a. paratuberculosis-infected animals and a control group. ing in vitro stimulation with PPD of whole blood for three different periods of time, IL-2R expression was detected mainly not only in γδ-T cells, but also in CD4+ and CD8+ T cells. We found a specific response of γδ-T cells from infected animals after 24 h of stimulation. Following 120 h of stimulation, however, γδ-T cells from control animals up-regulated IL-2R to the same level as those from infected animals, indicating either a non-specific stimulation or activation due to a first line of defence against mycobacterium antigens. The CD4+ cells showed a specific response to PPD stimulation at all three time points. A minor population of antigen reactive γδ+ cells also expressed CD8. The proliferative responses differed between αβ and γδ-T cells; the IL-2R+ αβ T cell population mainly comprised proliferating cells, while the γδ+ population showed less expansion.