Oral Presentation International Veterinary Immunology Symposium 2016

Cooperation of PD-1 and LAG-3 contributes to T-cell exhaustion in Anaplasma marginale-infected cattle (#7)

Tomohiro Okagawa 1 , Satoru Konnai 1 , James R Deringer 2 , Massaro W Ueti 3 , Glen A Scoles 3 , Shiro Murata 1 , Kazuhiko Ohashi 1 , Wendy C Brown 2
  1. Department of Disease Control, Graduate School of Veterinary Medicine, Hokkaido University, Sapporo, Hokkaido, Japan
  2. Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, WA, USA
  3. Animal Disease Research Unit, Agricultural Research Service, United States Department of Agriculture, Pullman, WA, USA

The CD4+ T-cell response is central for control of Anaplasma marginale infection in cattle. However, this infection induces a functional exhaustion of antigen-specific CD4+ T cells in cattle immunized with A. marginale outer membrane proteins or purified outer membranes (OM), which presumably facilitates persistence of this rickettsia. In the present study, we hypothesize that T-cell exhaustion following infection is induced by the upregulation of immunoinhibitory receptors on T cells, such as programmed death-1 (PD-1) and lymphocyte activation gene-3 (LAG-3). Therefore, OM-specific T-cell responses and the kinetics of PD-1+LAG-3+ exhausted T cells were monitored in A. marginale-challenged cattle previously immunized with OM.

Consistent with earlier studies, OM-specific T-cell proliferation and interferon-γ (IFN-γ) production were significantly suppressed in the challenged animals by five weeks post-infection (wpi). In addition, clinical signs, such as bacteremia and anemia, also peaked in these animals at 5 wpi. Flow cytometric analysis revealed that the percentages of PD-1+LAG-3+ exhausted T cells in the CD4+, CD8+, and γδ T-cell populations were gradually increased in the peripheral blood of the animals. Importantly, the highest percentages of these exhausted T-cell subsets were observed at 5 wpi, concurrent with the peak of functional exhaustion of OM-specific T cells and clinical signs. The immunoinhibitory ligand PD-L1 was also significantly upregulated on CD14+ antigen presenting cells in the peripheral blood of the challenged animals, following the same kinetics of the expression. Finally, in vitro blockade of the PD-1 and LAG-3 pathways by specific antibodies partially restored OM-specific T-cell proliferation and IFN-γ production at 5 wpi. Taken together, these results indicate that co-expression of PD-1 and LAG-3 on T cells contributes to the rapid exhaustion of A. marginale-specific CD4+ T cells following infection and that these immunoinhibitory receptors regulate T-cell responses during bovine anaplasmosis.