The role CD4+ CD25+ regulatory T cells (Treg) play in modulating the immune response has been investigated extensively over recent years. Much of the work to date has used the activation marker CD25 to define, enrich and deplete Treg. However, the identification of FoxP3 as a definitive marker of Treg has allowed us to study the effect of monoclonal antibodies against CD25 on regulatory T‐cell populations. Recently, published data have indicated that Treg are inactivated, not depleted, through treatment with anti‐CD25 monoclonal antibody. Using FoxP3‐Green fluorescent protein reporter mice, we show that treatment with the CD25 MoAb PC61 depleted a subpop ulation of Treg. The depleted Treg population expressed low levels of the CD69 marker, indicating an inactive phenotype. In addition, PC61 treatment altered the function of the remaining regulatory T‐cell population, preventing their ability to modulate autoimmune diseases. Thus, our results have important implications with regard to interpreting experimental outcomes from in vivo anti‐CD25 treatments.

This study was designed to develop a customized enzyme-linked immunosorbent assay (ELISA) for the serodiagnosis of Johne's disease (JD) in farmed deer. Two antigens were selected on the basis of their superior diagnostic readouts: denatured purified protein derivative (PPDj) and undenatured protoplasmic antigen (PpAg). ELISA development was based on the antigen reactivity of the immunoglobulin G1 (IgG1) isotype, which is a highly specific marker for mycobacterial disease seroreactivity in deer. Sensitivity estimates and test parameters were established using 102 Mycobacterium paratuberculosis-infected animals from more than 10 deer herds, and specificity estimates were determined using 508 uninfected animals from 5 known disease-free herds. A receiver-operated characteristic analysis determined that at a cut point of 50 ELISA units, there was a specificity of 99.5% and sensitivities of 84.0% with PPDj antigen, 88.0% with PpAg, and 91.0% when the antigens were used serially in a composite test. Estimated sensitivity was further improved using recombinant protein antigens unique for M. paratuberculosis, which identified infected animals that were unreactive to PPDj or PpAg. While 80% of animals that were seropositive in the IgG1 ELISA had detectable histopathology, the assay could also detect animals with subclinical disease. The test was significantly less sensitive (75%) for animals that were culture positive for M. paratuberculosis but with no detectable pathology than for those with pathological evidence of JD (>90%). When the IgG1 ELISA was used annually over a 4-year period in a deer herd with high levels of clinical JD, it eliminated clinical disease, increased production levels, and reduced JD-related mortality.

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